CINXE.COM

<!DOCTYPE html> <html class="client-nojs vector-feature-language-in-header-enabled vector-feature-language-in-main-page-header-disabled vector-feature-sticky-header-disabled vector-feature-page-tools-pinned-disabled vector-feature-toc-pinned-clientpref-1 vector-feature-main-menu-pinned-disabled vector-feature-limited-width-clientpref-1 vector-feature-limited-width-content-enabled vector-feature-custom-font-size-clientpref-1 vector-feature-appearance-pinned-clientpref-1 vector-feature-night-mode-enabled skin-theme-clientpref-day vector-toc-available" lang="en" dir="ltr"> <head> <meta charset="UTF-8"> <title>Second - Wikipedia</title> <script>(function(){var className="client-js vector-feature-language-in-header-enabled vector-feature-language-in-main-page-header-disabled vector-feature-sticky-header-disabled vector-feature-page-tools-pinned-disabled vector-feature-toc-pinned-clientpref-1 vector-feature-main-menu-pinned-disabled vector-feature-limited-width-clientpref-1 vector-feature-limited-width-content-enabled vector-feature-custom-font-size-clientpref-1 vector-feature-appearance-pinned-clientpref-1 vector-feature-night-mode-enabled skin-theme-clientpref-day vector-toc-available";var cookie=document.cookie.match(/(?:^|; )enwikimwclientpreferences=([^;]+)/);if(cookie){cookie[1].split('%2C').forEach(function(pref){className=className.replace(new RegExp('(^| )'+pref.replace(/-clientpref-\w+$|[^\w-]+/g,'')+'-clientpref-\\w+( |$)'),'$1'+pref+'$2');});}document.documentElement.className=className;}());RLCONF={"wgBreakFrames":false,"wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"dmy", "wgMonthNames":["","January","February","March","April","May","June","July","August","September","October","November","December"],"wgRequestId":"6c750396-19eb-4310-888e-bf78b3079a54","wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"Second","wgTitle":"Second","wgCurRevisionId":1256553341,"wgRevisionId":1256553341,"wgArticleId":26873,"wgIsArticle":true,"wgIsRedirect":false,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":["Articles with short description","Short description is different from Wikidata","Use mdy dates from September 2016","Use American English from September 2020","All Wikipedia articles written in American English","Articles containing Latin-language text","Commons link from Wikidata","Centimetre–gram–second system of units","Orders of magnitude (time)","SI base units","Units of time"],"wgPageViewLanguage":"en","wgPageContentLanguage":"en","wgPageContentModel":"wikitext","wgRelevantPageName": "Second","wgRelevantArticleId":26873,"wgIsProbablyEditable":true,"wgRelevantPageIsProbablyEditable":true,"wgRestrictionEdit":[],"wgRestrictionMove":[],"wgNoticeProject":"wikipedia","wgCiteReferencePreviewsActive":false,"wgFlaggedRevsParams":{"tags":{"status":{"levels":1}}},"wgMediaViewerOnClick":true,"wgMediaViewerEnabledByDefault":true,"wgPopupsFlags":0,"wgVisualEditor":{"pageLanguageCode":"en","pageLanguageDir":"ltr","pageVariantFallbacks":"en"},"wgMFDisplayWikibaseDescriptions":{"search":true,"watchlist":true,"tagline":false,"nearby":true},"wgWMESchemaEditAttemptStepOversample":false,"wgWMEPageLength":40000,"wgRelatedArticlesCompat":[],"wgCentralAuthMobileDomain":false,"wgEditSubmitButtonLabelPublish":true,"wgULSPosition":"interlanguage","wgULSisCompactLinksEnabled":false,"wgVector2022LanguageInHeader":true,"wgULSisLanguageSelectorEmpty":false,"wgWikibaseItemId":"Q11574","wgCheckUserClientHintsHeadersJsApi":["brands","architecture","bitness","fullVersionList","mobile","model", "platform","platformVersion"],"GEHomepageSuggestedEditsEnableTopics":true,"wgGETopicsMatchModeEnabled":false,"wgGEStructuredTaskRejectionReasonTextInputEnabled":false,"wgGELevelingUpEnabledForUser":false};RLSTATE={"ext.globalCssJs.user.styles":"ready","site.styles":"ready","user.styles":"ready","ext.globalCssJs.user":"ready","user":"ready","user.options":"loading","ext.cite.styles":"ready","ext.math.styles":"ready","skins.vector.search.codex.styles":"ready","skins.vector.styles":"ready","skins.vector.icons":"ready","jquery.makeCollapsible.styles":"ready","ext.wikimediamessages.styles":"ready","ext.visualEditor.desktopArticleTarget.noscript":"ready","ext.uls.interlanguage":"ready","wikibase.client.init":"ready","ext.wikimediaBadges":"ready"};RLPAGEMODULES=["ext.cite.ux-enhancements","site","mediawiki.page.ready","jquery.makeCollapsible","mediawiki.toc","skins.vector.js","ext.centralNotice.geoIP","ext.centralNotice.startUp","ext.gadget.ReferenceTooltips","ext.gadget.switcher", "ext.urlShortener.toolbar","ext.centralauth.centralautologin","mmv.bootstrap","ext.popups","ext.visualEditor.desktopArticleTarget.init","ext.visualEditor.targetLoader","ext.echo.centralauth","ext.eventLogging","ext.wikimediaEvents","ext.navigationTiming","ext.uls.interface","ext.cx.eventlogging.campaigns","ext.cx.uls.quick.actions","wikibase.client.vector-2022","ext.checkUser.clientHints","ext.quicksurveys.init","ext.growthExperiments.SuggestedEditSession","wikibase.sidebar.tracking"];</script> <script>(RLQ=window.RLQ||[]).push(function(){mw.loader.impl(function(){return["user.options@12s5i",function($,jQuery,require,module){mw.user.tokens.set({"patrolToken":"+\\","watchToken":"+\\","csrfToken":"+\\"}); }];});});</script> <link rel="stylesheet" href="/w/load.php?lang=en&modules=ext.cite.styles%7Cext.math.styles%7Cext.uls.interlanguage%7Cext.visualEditor.desktopArticleTarget.noscript%7Cext.wikimediaBadges%7Cext.wikimediamessages.styles%7Cjquery.makeCollapsible.styles%7Cskins.vector.icons%2Cstyles%7Cskins.vector.search.codex.styles%7Cwikibase.client.init&only=styles&skin=vector-2022"> <script async="" src="/w/load.php?lang=en&modules=startup&only=scripts&raw=1&skin=vector-2022"></script> <meta name="ResourceLoaderDynamicStyles" content=""> <link rel="stylesheet" href="/w/load.php?lang=en&modules=site.styles&only=styles&skin=vector-2022"> <meta name="generator" content="MediaWiki 1.44.0-wmf.4"> <meta name="referrer" content="origin"> <meta name="referrer" content="origin-when-cross-origin"> <meta name="robots" content="max-image-preview:standard"> <meta name="format-detection" content="telephone=no"> <meta property="og:image" content="https://upload.wikimedia.org/wikipedia/commons/1/15/Clock-pendulum.gif"> <meta property="og:image:width" content="1200"> <meta property="og:image:height" content="2274"> <meta property="og:image" content="https://upload.wikimedia.org/wikipedia/commons/1/15/Clock-pendulum.gif"> <meta property="og:image:width" content="800"> <meta property="og:image:height" content="1516"> <meta property="og:image:width" content="640"> <meta property="og:image:height" content="1213"> <meta name="viewport" content="width=1120"> <meta property="og:title" content="Second - Wikipedia"> <meta property="og:type" content="website"> <link rel="preconnect" href="//upload.wikimedia.org"> <link rel="alternate" media="only screen and (max-width: 640px)" href="//en.m.wikipedia.org/wiki/Second"> <link rel="alternate" type="application/x-wiki" title="Edit this page" href="/w/index.php?title=Second&action=edit"> <link rel="apple-touch-icon" href="/static/apple-touch/wikipedia.png"> <link rel="icon" href="/static/favicon/wikipedia.ico"> <link rel="search" type="application/opensearchdescription+xml" href="/w/rest.php/v1/search" title="Wikipedia (en)"> <link rel="EditURI" type="application/rsd+xml" href="//en.wikipedia.org/w/api.php?action=rsd"> <link rel="canonical" href="https://en.wikipedia.org/wiki/Second"> <link rel="license" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en"> <link rel="alternate" type="application/atom+xml" title="Wikipedia Atom feed" href="/w/index.php?title=Special:RecentChanges&feed=atom"> <link rel="dns-prefetch" href="//meta.wikimedia.org" /> <link rel="dns-prefetch" href="//login.wikimedia.org"> </head> <body class="skin--responsive skin-vector skin-vector-search-vue mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject mw-editable page-Second rootpage-Second skin-vector-2022 action-view"><a class="mw-jump-link" href="#bodyContent">Jump to content</a> <div class="vector-header-container"> <header class="vector-header mw-header"> <div class="vector-header-start"> <nav class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-dropdown" class="vector-dropdown vector-main-menu-dropdown vector-button-flush-left vector-button-flush-right" > <input type="checkbox" id="vector-main-menu-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-main-menu-dropdown" class="vector-dropdown-checkbox " aria-label="Main menu" > <label id="vector-main-menu-dropdown-label" for="vector-main-menu-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-menu mw-ui-icon-wikimedia-menu"></span> <span class="vector-dropdown-label-text">Main menu</span> </label> <div class="vector-dropdown-content"> <div id="vector-main-menu-unpinned-container" class="vector-unpinned-container"> <div id="vector-main-menu" class="vector-main-menu vector-pinnable-element"> <div class="vector-pinnable-header vector-main-menu-pinnable-header vector-pinnable-header-unpinned" data-feature-name="main-menu-pinned" data-pinnable-element-id="vector-main-menu" data-pinned-container-id="vector-main-menu-pinned-container" data-unpinned-container-id="vector-main-menu-unpinned-container" > <div class="vector-pinnable-header-label">Main menu</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-main-menu.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-main-menu.unpin">hide</button> </div> <div id="p-navigation" class="vector-menu mw-portlet mw-portlet-navigation" > <div class="vector-menu-heading"> Navigation </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="n-mainpage-description" class="mw-list-item"><a href="/wiki/Main_Page" title="Visit the main page [z]" accesskey="z"><span>Main page</span></a></li><li id="n-contents" class="mw-list-item"><a href="/wiki/Wikipedia:Contents" title="Guides to browsing Wikipedia"><span>Contents</span></a></li><li id="n-currentevents" class="mw-list-item"><a href="/wiki/Portal:Current_events" title="Articles related to current events"><span>Current events</span></a></li><li id="n-randompage" class="mw-list-item"><a href="/wiki/Special:Random" title="Visit a randomly selected article [x]" accesskey="x"><span>Random article</span></a></li><li id="n-aboutsite" class="mw-list-item"><a href="/wiki/Wikipedia:About" title="Learn about Wikipedia and how it works"><span>About Wikipedia</span></a></li><li id="n-contactpage" class="mw-list-item"><a href="//en.wikipedia.org/wiki/Wikipedia:Contact_us" title="How to contact Wikipedia"><span>Contact us</span></a></li> </ul> </div> </div> <div id="p-interaction" class="vector-menu mw-portlet mw-portlet-interaction" > <div class="vector-menu-heading"> Contribute </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="n-help" class="mw-list-item"><a href="/wiki/Help:Contents" title="Guidance on how to use and edit Wikipedia"><span>Help</span></a></li><li id="n-introduction" class="mw-list-item"><a href="/wiki/Help:Introduction" title="Learn how to edit Wikipedia"><span>Learn to edit</span></a></li><li id="n-portal" class="mw-list-item"><a href="/wiki/Wikipedia:Community_portal" title="The hub for editors"><span>Community portal</span></a></li><li id="n-recentchanges" class="mw-list-item"><a href="/wiki/Special:RecentChanges" title="A list of recent changes to Wikipedia [r]" accesskey="r"><span>Recent changes</span></a></li><li id="n-upload" class="mw-list-item"><a href="/wiki/Wikipedia:File_upload_wizard" title="Add images or other media for use on Wikipedia"><span>Upload file</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> <a href="/wiki/Main_Page" class="mw-logo"> <img class="mw-logo-icon" src="/static/images/icons/wikipedia.png" alt="" aria-hidden="true" height="50" width="50"> <span class="mw-logo-container skin-invert"> <img class="mw-logo-wordmark" alt="Wikipedia" src="/static/images/mobile/copyright/wikipedia-wordmark-en.svg" style="width: 7.5em; height: 1.125em;"> <img class="mw-logo-tagline" alt="The Free Encyclopedia" src="/static/images/mobile/copyright/wikipedia-tagline-en.svg" width="117" height="13" style="width: 7.3125em; height: 0.8125em;"> </span> </a> </div> <div class="vector-header-end"> <div id="p-search" role="search" class="vector-search-box-vue vector-search-box-collapses vector-search-box-show-thumbnail vector-search-box-auto-expand-width vector-search-box"> <a href="/wiki/Special:Search" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only search-toggle" title="Search Wikipedia [f]" accesskey="f"><span class="vector-icon mw-ui-icon-search mw-ui-icon-wikimedia-search"></span> <span>Search</span> </a> <div class="vector-typeahead-search-container"> <div class="cdx-typeahead-search cdx-typeahead-search--show-thumbnail cdx-typeahead-search--auto-expand-width"> <form action="/w/index.php" id="searchform" class="cdx-search-input cdx-search-input--has-end-button"> <div id="simpleSearch" class="cdx-search-input__input-wrapper" data-search-loc="header-moved"> <div class="cdx-text-input cdx-text-input--has-start-icon"> <input class="cdx-text-input__input" type="search" name="search" placeholder="Search Wikipedia" aria-label="Search Wikipedia" autocapitalize="sentences" title="Search Wikipedia [f]" accesskey="f" id="searchInput" > <span class="cdx-text-input__icon cdx-text-input__start-icon"></span> </div> <input type="hidden" name="title" value="Special:Search"> </div> <button class="cdx-button cdx-search-input__end-button">Search</button> </form> </div> </div> </div> <nav class="vector-user-links vector-user-links-wide" aria-label="Personal tools"> <div class="vector-user-links-main"> <div id="p-vector-user-menu-preferences" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <div id="p-vector-user-menu-userpage" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-dropdown" class="vector-dropdown " title="Change the appearance of the page's font size, width, and color" > <input type="checkbox" id="vector-appearance-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-appearance-dropdown" class="vector-dropdown-checkbox " aria-label="Appearance" > <label id="vector-appearance-dropdown-label" for="vector-appearance-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-appearance mw-ui-icon-wikimedia-appearance"></span> <span class="vector-dropdown-label-text">Appearance</span> </label> <div class="vector-dropdown-content"> <div id="vector-appearance-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <div id="p-vector-user-menu-notifications" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <div id="p-vector-user-menu-overflow" class="vector-menu mw-portlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="https://donate.wikimedia.org/wiki/Special:FundraiserRedirector?utm_source=donate&utm_medium=sidebar&utm_campaign=C13_en.wikipedia.org&uselang=en" class=""><span>Donate</span></a> </li> <li id="pt-createaccount-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="/w/index.php?title=Special:CreateAccount&returnto=Second" title="You are encouraged to create an account and log in; however, it is not mandatory" class=""><span>Create account</span></a> </li> <li id="pt-login-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="/w/index.php?title=Special:UserLogin&returnto=Second" title="You're encouraged to log in; however, it's not mandatory. [o]" accesskey="o" class=""><span>Log in</span></a> </li> </ul> </div> </div> </div> <div id="vector-user-links-dropdown" class="vector-dropdown vector-user-menu vector-button-flush-right vector-user-menu-logged-out" title="Log in and more options" > <input type="checkbox" id="vector-user-links-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-user-links-dropdown" class="vector-dropdown-checkbox " aria-label="Personal tools" > <label id="vector-user-links-dropdown-label" for="vector-user-links-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-ellipsis mw-ui-icon-wikimedia-ellipsis"></span> <span class="vector-dropdown-label-text">Personal tools</span> </label> <div class="vector-dropdown-content"> <div id="p-personal" class="vector-menu mw-portlet mw-portlet-personal user-links-collapsible-item" title="User menu" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport" class="user-links-collapsible-item mw-list-item"><a href="https://donate.wikimedia.org/wiki/Special:FundraiserRedirector?utm_source=donate&utm_medium=sidebar&utm_campaign=C13_en.wikipedia.org&uselang=en"><span>Donate</span></a></li><li id="pt-createaccount" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:CreateAccount&returnto=Second" title="You are encouraged to create an account and log in; however, it is not mandatory"><span class="vector-icon mw-ui-icon-userAdd mw-ui-icon-wikimedia-userAdd"></span> <span>Create account</span></a></li><li id="pt-login" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:UserLogin&returnto=Second" title="You're encouraged to log in; however, it's not mandatory. [o]" accesskey="o"><span class="vector-icon mw-ui-icon-logIn mw-ui-icon-wikimedia-logIn"></span> <span>Log in</span></a></li> </ul> </div> </div> <div id="p-user-menu-anon-editor" class="vector-menu mw-portlet mw-portlet-user-menu-anon-editor" > <div class="vector-menu-heading"> Pages for logged out editors <a href="/wiki/Help:Introduction" aria-label="Learn more about editing"><span>learn more</span></a> </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-anoncontribs" class="mw-list-item"><a href="/wiki/Special:MyContributions" title="A list of edits made from this IP address [y]" accesskey="y"><span>Contributions</span></a></li><li id="pt-anontalk" class="mw-list-item"><a href="/wiki/Special:MyTalk" title="Discussion about edits from this IP address [n]" accesskey="n"><span>Talk</span></a></li> </ul> </div> </div> </div> </div> </nav> </div> </header> </div> <div class="mw-page-container"> <div class="mw-page-container-inner"> <div class="vector-sitenotice-container"> <div id="siteNotice"></div> </div> <div class="vector-column-start"> <div class="vector-main-menu-container"> <div id="mw-navigation"> <nav id="mw-panel" class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-pinned-container" class="vector-pinned-container"> </div> </nav> </div> </div> <div class="vector-sticky-pinned-container"> <nav id="mw-panel-toc" aria-label="Contents" data-event-name="ui.sidebar-toc" class="mw-table-of-contents-container vector-toc-landmark"> <div id="vector-toc-pinned-container" class="vector-pinned-container"> <div id="vector-toc" class="vector-toc vector-pinnable-element"> <div class="vector-pinnable-header vector-toc-pinnable-header vector-pinnable-header-pinned" data-feature-name="toc-pinned" data-pinnable-element-id="vector-toc" > <h2 class="vector-pinnable-header-label">Contents</h2> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-toc.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-toc.unpin">hide</button> </div> <ul class="vector-toc-contents" id="mw-panel-toc-list"> <li id="toc-mw-content-text" class="vector-toc-list-item vector-toc-level-1"> <a href="#" class="vector-toc-link"> <div class="vector-toc-text">(Top)</div> </a> </li> <li id="toc-Etymology" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Etymology"> <div class="vector-toc-text"> <span class="vector-toc-numb">1</span> <span>Etymology</span> </div> </a> <ul id="toc-Etymology-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Uses" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Uses"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Uses</span> </div> </a> <ul id="toc-Uses-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Clocks_and_solar_time" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Clocks_and_solar_time"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Clocks and solar time</span> </div> </a> <ul id="toc-Clocks_and_solar_time-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Events_and_units_of_time_in_seconds" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Events_and_units_of_time_in_seconds"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Events and units of time in seconds</span> </div> </a> <ul id="toc-Events_and_units_of_time_in_seconds-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Other_units_incorporating_seconds" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Other_units_incorporating_seconds"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Other units incorporating seconds</span> </div> </a> <ul id="toc-Other_units_incorporating_seconds-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Timekeeping_standards" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Timekeeping_standards"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Timekeeping standards</span> </div> </a> <button aria-controls="toc-Timekeeping_standards-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Timekeeping standards subsection</span> </button> <ul id="toc-Timekeeping_standards-sublist" class="vector-toc-list"> <li id="toc-Optical_lattice_clock" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Optical_lattice_clock"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.1</span> <span>Optical lattice clock</span> </div> </a> <ul id="toc-Optical_lattice_clock-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-History_of_definition" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#History_of_definition"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>History of definition</span> </div> </a> <button aria-controls="toc-History_of_definition-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle History of definition subsection</span> </button> <ul id="toc-History_of_definition-sublist" class="vector-toc-list"> <li id="toc-Sexagesimal_divisions_of_calendar_time_and_day" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Sexagesimal_divisions_of_calendar_time_and_day"> <div class="vector-toc-text"> <span class="vector-toc-numb">7.1</span> <span>Sexagesimal divisions of calendar time and day</span> </div> </a> <ul id="toc-Sexagesimal_divisions_of_calendar_time_and_day-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Fraction_of_solar_day" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Fraction_of_solar_day"> <div class="vector-toc-text"> <span class="vector-toc-numb">7.2</span> <span>Fraction of solar day</span> </div> </a> <ul id="toc-Fraction_of_solar_day-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Fraction_of_an_ephemeris_year" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Fraction_of_an_ephemeris_year"> <div class="vector-toc-text"> <span class="vector-toc-numb">7.3</span> <span>Fraction of an ephemeris year</span> </div> </a> <ul id="toc-Fraction_of_an_ephemeris_year-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Atomic_definition" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Atomic_definition"> <div class="vector-toc-text"> <span class="vector-toc-numb">7.4</span> <span>Atomic definition</span> </div> </a> <ul id="toc-Atomic_definition-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Table" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Table"> <div class="vector-toc-text"> <span class="vector-toc-numb">7.5</span> <span>Table</span> </div> </a> <ul id="toc-Table-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Future_redefinition" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Future_redefinition"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>Future redefinition</span> </div> </a> <button aria-controls="toc-Future_redefinition-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Future redefinition subsection</span> </button> <ul id="toc-Future_redefinition-sublist" class="vector-toc-list"> <li id="toc-Rydberg_constant" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Rydberg_constant"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.1</span> <span>Rydberg constant</span> </div> </a> <ul id="toc-Rydberg_constant-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Requirements" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Requirements"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.2</span> <span>Requirements</span> </div> </a> <ul id="toc-Requirements-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-SI_multiples" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#SI_multiples"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>SI multiples</span> </div> </a> <ul id="toc-SI_multiples-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">10</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Notes" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Notes"> <div class="vector-toc-text"> <span class="vector-toc-numb">11</span> <span>Notes</span> </div> </a> <ul id="toc-Notes-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">12</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">13</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Second</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 160 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-160" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">160 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-af mw-list-item"><a href="https://af.wikipedia.org/wiki/Sekonde" title="Sekonde – Afrikaans" lang="af" hreflang="af" data-title="Sekonde" data-language-autonym="Afrikaans" data-language-local-name="Afrikaans" class="interlanguage-link-target"><span>Afrikaans</span></a></li><li class="interlanguage-link interwiki-als mw-list-item"><a href="https://als.wikipedia.org/wiki/Sekunde" title="Sekunde – Alemannic" lang="gsw" hreflang="gsw" data-title="Sekunde" data-language-autonym="Alemannisch" data-language-local-name="Alemannic" class="interlanguage-link-target"><span>Alemannisch</span></a></li><li class="interlanguage-link interwiki-am mw-list-item"><a href="https://am.wikipedia.org/wiki/%E1%88%B4%E1%8A%AE%E1%8A%95%E1%8B%B5" title="ሴኮንድ – Amharic" lang="am" hreflang="am" data-title="ሴኮንድ" data-language-autonym="አማርኛ" data-language-local-name="Amharic" class="interlanguage-link-target"><span>አማርኛ</span></a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%AB%D8%A7%D9%86%D9%8A%D8%A9" title="ثانية – Arabic" lang="ar" hreflang="ar" data-title="ثانية" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-an mw-list-item"><a href="https://an.wikipedia.org/wiki/Segundo" title="Segundo – Aragonese" lang="an" hreflang="an" data-title="Segundo" data-language-autonym="Aragonés" data-language-local-name="Aragonese" class="interlanguage-link-target"><span>Aragonés</span></a></li><li class="interlanguage-link interwiki-arc mw-list-item"><a href="https://arc.wikipedia.org/wiki/%DC%AA%DC%A6%DC%A6%DC%90" title="ܪܦܦܐ – Aramaic" lang="arc" hreflang="arc" data-title="ܪܦܦܐ" data-language-autonym="ܐܪܡܝܐ" data-language-local-name="Aramaic" class="interlanguage-link-target"><span>ܐܪܡܝܐ</span></a></li><li class="interlanguage-link interwiki-hyw mw-list-item"><a href="https://hyw.wikipedia.org/wiki/%D4%B5%D6%80%D5%AF%D5%BE%D5%A1%D5%B5%D6%80%D5%AF%D5%A5%D5%A1%D5%B6" title="Երկվայրկեան – Western Armenian" lang="hyw" hreflang="hyw" data-title="Երկվայրկեան" data-language-autonym="Արեւմտահայերէն" data-language-local-name="Western Armenian" class="interlanguage-link-target"><span>Արեւմտահայերէն</span></a></li><li class="interlanguage-link interwiki-as mw-list-item"><a href="https://as.wikipedia.org/wiki/%E0%A6%9B%E0%A7%87%E0%A6%95%E0%A7%87%E0%A6%A3%E0%A7%8D%E0%A6%A1" title="ছেকেণ্ড – Assamese" lang="as" hreflang="as" data-title="ছেকেণ্ড" data-language-autonym="অসমীয়া" data-language-local-name="Assamese" class="interlanguage-link-target"><span>অসমীয়া</span></a></li><li class="interlanguage-link interwiki-ast mw-list-item"><a href="https://ast.wikipedia.org/wiki/Segundu" title="Segundu – Asturian" lang="ast" hreflang="ast" data-title="Segundu" data-language-autonym="Asturianu" data-language-local-name="Asturian" class="interlanguage-link-target"><span>Asturianu</span></a></li><li class="interlanguage-link interwiki-gn mw-list-item"><a href="https://gn.wikipedia.org/wiki/Aravo%27ive" title="Aravo'ive – Guarani" lang="gn" hreflang="gn" data-title="Aravo'ive" data-language-autonym="Avañe'ẽ" data-language-local-name="Guarani" class="interlanguage-link-target"><span>Avañe'ẽ</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/Saniy%C9%99" title="Saniyə – Azerbaijani" lang="az" hreflang="az" data-title="Saniyə" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-azb mw-list-item"><a href="https://azb.wikipedia.org/wiki/%D8%AB%D8%A7%D9%86%DB%8C%D9%87" title="ثانیه – South Azerbaijani" lang="azb" hreflang="azb" data-title="ثانیه" data-language-autonym="تۆرکجه" data-language-local-name="South Azerbaijani" class="interlanguage-link-target"><span>تۆرکجه</span></a></li><li class="interlanguage-link interwiki-ban mw-list-item"><a href="https://ban.wikipedia.org/wiki/Detik" title="Detik – Balinese" lang="ban" hreflang="ban" data-title="Detik" data-language-autonym="Basa Bali" data-language-local-name="Balinese" class="interlanguage-link-target"><span>Basa Bali</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%B8%E0%A7%87%E0%A6%95%E0%A7%87%E0%A6%A8%E0%A7%8D%E0%A6%A1" title="সেকেন্ড – Bangla" lang="bn" hreflang="bn" data-title="সেকেন্ড" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-zh-min-nan mw-list-item"><a href="https://zh-min-nan.wikipedia.org/wiki/Bi%C3%B3" title="Bió – Minnan" lang="nan" hreflang="nan" data-title="Bió" data-language-autonym="閩南語 / Bân-lâm-gú" data-language-local-name="Minnan" class="interlanguage-link-target"><span>閩南語 / Bân-lâm-gú</span></a></li><li class="interlanguage-link interwiki-ba mw-list-item"><a href="https://ba.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4" title="Секунд – Bashkir" lang="ba" hreflang="ba" data-title="Секунд" data-language-autonym="Башҡортса" data-language-local-name="Bashkir" class="interlanguage-link-target"><span>Башҡортса</span></a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4%D0%B0" title="Секунда – Belarusian" lang="be" hreflang="be" data-title="Секунда" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target"><span>Беларуская</span></a></li><li class="interlanguage-link interwiki-be-x-old mw-list-item"><a href="https://be-tarask.wikipedia.org/wiki/%D0%A1%D1%8D%D0%BA%D1%83%D0%BD%D0%B4%D0%B0" title="Сэкунда – Belarusian (Taraškievica orthography)" lang="be-tarask" hreflang="be-tarask" data-title="Сэкунда" data-language-autonym="Беларуская (тарашкевіца)" data-language-local-name="Belarusian (Taraškievica orthography)" class="interlanguage-link-target"><span>Беларуская (тарашкевіца)</span></a></li><li class="interlanguage-link interwiki-bcl mw-list-item"><a href="https://bcl.wikipedia.org/wiki/Segundo" title="Segundo – Central Bikol" lang="bcl" hreflang="bcl" data-title="Segundo" data-language-autonym="Bikol Central" data-language-local-name="Central Bikol" class="interlanguage-link-target"><span>Bikol Central</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4%D0%B0" title="Секунда – Bulgarian" lang="bg" hreflang="bg" data-title="Секунда" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bar mw-list-item"><a href="https://bar.wikipedia.org/wiki/Sekund" title="Sekund – Bavarian" lang="bar" hreflang="bar" data-title="Sekund" data-language-autonym="Boarisch" data-language-local-name="Bavarian" class="interlanguage-link-target"><span>Boarisch</span></a></li><li class="interlanguage-link interwiki-bo mw-list-item"><a href="https://bo.wikipedia.org/wiki/%E0%BD%A6%E0%BE%90%E0%BD%A2%E0%BC%8B%E0%BD%86%E0%BC%8D" title="སྐར་ཆ། – Tibetan" lang="bo" hreflang="bo" data-title="སྐར་ཆ།" data-language-autonym="བོད་ཡིག" data-language-local-name="Tibetan" class="interlanguage-link-target"><span>བོད་ཡིག</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/Sekunda" title="Sekunda – Bosnian" lang="bs" hreflang="bs" data-title="Sekunda" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-br mw-list-item"><a href="https://br.wikipedia.org/wiki/Eilenn_(amzer)" title="Eilenn (amzer) – Breton" lang="br" hreflang="br" data-title="Eilenn (amzer)" data-language-autonym="Brezhoneg" data-language-local-name="Breton" class="interlanguage-link-target"><span>Brezhoneg</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Segon" title="Segon – Catalan" lang="ca" hreflang="ca" data-title="Segon" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cv mw-list-item"><a href="https://cv.wikipedia.org/wiki/%C3%87%D0%B5%D0%BA%D0%BA%D1%83%D0%BD%D1%82" title="Çеккунт – Chuvash" lang="cv" hreflang="cv" data-title="Çеккунт" data-language-autonym="Чӑвашла" data-language-local-name="Chuvash" class="interlanguage-link-target"><span>Чӑвашла</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Sekunda" title="Sekunda – Czech" lang="cs" hreflang="cs" data-title="Sekunda" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-sn mw-list-item"><a href="https://sn.wikipedia.org/wiki/Chepiri" title="Chepiri – Shona" lang="sn" hreflang="sn" data-title="Chepiri" data-language-autonym="ChiShona" data-language-local-name="Shona" class="interlanguage-link-target"><span>ChiShona</span></a></li><li class="interlanguage-link interwiki-cy mw-list-item"><a href="https://cy.wikipedia.org/wiki/Eiliad" title="Eiliad – Welsh" lang="cy" hreflang="cy" data-title="Eiliad" data-language-autonym="Cymraeg" data-language-local-name="Welsh" class="interlanguage-link-target"><span>Cymraeg</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Sekund" title="Sekund – Danish" lang="da" hreflang="da" data-title="Sekund" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-ary mw-list-item"><a href="https://ary.wikipedia.org/wiki/%D8%AA%D8%A7%D9%86%D9%8A%D8%A9" title="تانية – Moroccan Arabic" lang="ary" hreflang="ary" data-title="تانية" data-language-autonym="الدارجة" data-language-local-name="Moroccan Arabic" class="interlanguage-link-target"><span>الدارجة</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Sekunde" title="Sekunde – German" lang="de" hreflang="de" data-title="Sekunde" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Sekund" title="Sekund – Estonian" lang="et" hreflang="et" data-title="Sekund" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%94%CE%B5%CF%85%CF%84%CE%B5%CF%81%CF%8C%CE%BB%CE%B5%CF%80%CF%84%CE%BF" title="Δευτερόλεπτο – Greek" lang="el" hreflang="el" data-title="Δευτερόλεπτο" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Segundo" title="Segundo – Spanish" lang="es" hreflang="es" data-title="Segundo" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Sekundo" title="Sekundo – Esperanto" lang="eo" hreflang="eo" data-title="Sekundo" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Segundo" title="Segundo – Basque" lang="eu" hreflang="eu" data-title="Segundo" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%AB%D8%A7%D9%86%DB%8C%D9%87" title="ثانیه – Persian" lang="fa" hreflang="fa" data-title="ثانیه" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-hif mw-list-item"><a href="https://hif.wikipedia.org/wiki/Second" title="Second – Fiji Hindi" lang="hif" hreflang="hif" data-title="Second" data-language-autonym="Fiji Hindi" data-language-local-name="Fiji Hindi" class="interlanguage-link-target"><span>Fiji Hindi</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Seconde_(temps)" title="Seconde (temps) – French" lang="fr" hreflang="fr" data-title="Seconde (temps)" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-fy mw-list-item"><a href="https://fy.wikipedia.org/wiki/Sekonde" title="Sekonde – Western Frisian" lang="fy" hreflang="fy" data-title="Sekonde" data-language-autonym="Frysk" data-language-local-name="Western Frisian" class="interlanguage-link-target"><span>Frysk</span></a></li><li class="interlanguage-link interwiki-fur mw-list-item"><a href="https://fur.wikipedia.org/wiki/Secont" title="Secont – Friulian" lang="fur" hreflang="fur" data-title="Secont" data-language-autonym="Furlan" data-language-local-name="Friulian" class="interlanguage-link-target"><span>Furlan</span></a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/Soicind" title="Soicind – Irish" lang="ga" hreflang="ga" data-title="Soicind" data-language-autonym="Gaeilge" data-language-local-name="Irish" class="interlanguage-link-target"><span>Gaeilge</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Segundo" title="Segundo – Galician" lang="gl" hreflang="gl" data-title="Segundo" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-gan mw-list-item"><a href="https://gan.wikipedia.org/wiki/%E7%A7%92" title="秒 – Gan" lang="gan" hreflang="gan" data-title="秒" data-language-autonym="贛語" data-language-local-name="Gan" class="interlanguage-link-target"><span>贛語</span></a></li><li class="interlanguage-link interwiki-gu mw-list-item"><a href="https://gu.wikipedia.org/wiki/%E0%AA%B8%E0%AB%87%E0%AA%95%E0%AA%A8%E0%AB%8D%E0%AA%A1" title="સેકન્ડ – Gujarati" lang="gu" hreflang="gu" data-title="સેકન્ડ" data-language-autonym="ગુજરાતી" data-language-local-name="Gujarati" class="interlanguage-link-target"><span>ગુજરાતી</span></a></li><li class="interlanguage-link interwiki-hak mw-list-item"><a href="https://hak.wikipedia.org/wiki/Mi%C3%A9u" title="Miéu – Hakka Chinese" lang="hak" hreflang="hak" data-title="Miéu" data-language-autonym="客家語 / Hak-kâ-ngî" data-language-local-name="Hakka Chinese" class="interlanguage-link-target"><span>客家語 / Hak-kâ-ngî</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%B4%88_(%EC%8B%9C%EA%B0%84)" title="초 (시간) – Korean" lang="ko" hreflang="ko" data-title="초 (시간)" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-ha mw-list-item"><a href="https://ha.wikipedia.org/wiki/Sakan" title="Sakan – Hausa" lang="ha" hreflang="ha" data-title="Sakan" data-language-autonym="Hausa" data-language-local-name="Hausa" class="interlanguage-link-target"><span>Hausa</span></a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D5%8E%D5%A1%D5%B5%D6%80%D5%AF%D5%B5%D5%A1%D5%B6" title="Վայրկյան – Armenian" lang="hy" hreflang="hy" data-title="Վայրկյան" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%B8%E0%A5%87%E0%A4%95%E0%A5%87%E0%A4%82%E0%A4%A1" title="सेकेंड – Hindi" lang="hi" hreflang="hi" data-title="सेकेंड" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/Sekunda" title="Sekunda – Croatian" lang="hr" hreflang="hr" data-title="Sekunda" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-io mw-list-item"><a href="https://io.wikipedia.org/wiki/Sekundo" title="Sekundo – Ido" lang="io" hreflang="io" data-title="Sekundo" data-language-autonym="Ido" data-language-local-name="Ido" class="interlanguage-link-target"><span>Ido</span></a></li><li class="interlanguage-link interwiki-ilo mw-list-item"><a href="https://ilo.wikipedia.org/wiki/Segundo" title="Segundo – Iloko" lang="ilo" hreflang="ilo" data-title="Segundo" data-language-autonym="Ilokano" data-language-local-name="Iloko" class="interlanguage-link-target"><span>Ilokano</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Detik" title="Detik – Indonesian" lang="id" hreflang="id" data-title="Detik" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-ia mw-list-item"><a href="https://ia.wikipedia.org/wiki/Secunda" title="Secunda – Interlingua" lang="ia" hreflang="ia" data-title="Secunda" data-language-autonym="Interlingua" data-language-local-name="Interlingua" class="interlanguage-link-target"><span>Interlingua</span></a></li><li class="interlanguage-link interwiki-ie mw-list-item"><a href="https://ie.wikipedia.org/wiki/Seconde" title="Seconde – Interlingue" lang="ie" hreflang="ie" data-title="Seconde" data-language-autonym="Interlingue" data-language-local-name="Interlingue" class="interlanguage-link-target"><span>Interlingue</span></a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/Sek%C3%BAnda" title="Sekúnda – Icelandic" lang="is" hreflang="is" data-title="Sekúnda" data-language-autonym="Íslenska" data-language-local-name="Icelandic" class="interlanguage-link-target"><span>Íslenska</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Secondo" title="Secondo – Italian" lang="it" hreflang="it" data-title="Secondo" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%A9%D7%A0%D7%99%D7%99%D7%94" title="שנייה – Hebrew" lang="he" hreflang="he" data-title="שנייה" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-jv mw-list-item"><a href="https://jv.wikipedia.org/wiki/Detik" title="Detik – Javanese" lang="jv" hreflang="jv" data-title="Detik" data-language-autonym="Jawa" data-language-local-name="Javanese" class="interlanguage-link-target"><span>Jawa</span></a></li><li class="interlanguage-link interwiki-kbp mw-list-item"><a href="https://kbp.wikipedia.org/wiki/K%C9%9Bl%C9%9Bmk%C9%9Bl%C9%9Bm" title="Kɛlɛmkɛlɛm – Kabiye" lang="kbp" hreflang="kbp" data-title="Kɛlɛmkɛlɛm" data-language-autonym="Kabɩyɛ" data-language-local-name="Kabiye" class="interlanguage-link-target"><span>Kabɩyɛ</span></a></li><li class="interlanguage-link interwiki-krc mw-list-item"><a href="https://krc.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4" title="Секунд – Karachay-Balkar" lang="krc" hreflang="krc" data-title="Секунд" data-language-autonym="Къарачай-малкъар" data-language-local-name="Karachay-Balkar" class="interlanguage-link-target"><span>Къарачай-малкъар</span></a></li><li class="interlanguage-link interwiki-ka mw-list-item"><a href="https://ka.wikipedia.org/wiki/%E1%83%AC%E1%83%90%E1%83%9B%E1%83%98" title="წამი – Georgian" lang="ka" hreflang="ka" data-title="წამი" data-language-autonym="ქართული" data-language-local-name="Georgian" class="interlanguage-link-target"><span>ქართული</span></a></li><li class="interlanguage-link interwiki-ks mw-list-item"><a href="https://ks.wikipedia.org/wiki/%D8%B3%D8%A0%DA%A9%D9%8E%D9%86%D9%9B%DA%88" title="سؠکَنٛڈ – Kashmiri" lang="ks" hreflang="ks" data-title="سؠکَنٛڈ" data-language-autonym="कॉशुर / کٲشُر" data-language-local-name="Kashmiri" class="interlanguage-link-target"><span>कॉशुर / کٲشُر</span></a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4" title="Секунд – Kazakh" lang="kk" hreflang="kk" data-title="Секунд" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-kw mw-list-item"><a href="https://kw.wikipedia.org/wiki/Eylen" title="Eylen – Cornish" lang="kw" hreflang="kw" data-title="Eylen" data-language-autonym="Kernowek" data-language-local-name="Cornish" class="interlanguage-link-target"><span>Kernowek</span></a></li><li class="interlanguage-link interwiki-sw mw-list-item"><a href="https://sw.wikipedia.org/wiki/Sekunde" title="Sekunde – Swahili" lang="sw" hreflang="sw" data-title="Sekunde" data-language-autonym="Kiswahili" data-language-local-name="Swahili" class="interlanguage-link-target"><span>Kiswahili</span></a></li><li class="interlanguage-link interwiki-ht mw-list-item"><a href="https://ht.wikipedia.org/wiki/Segond_(tan)" title="Segond (tan) – Haitian Creole" lang="ht" hreflang="ht" data-title="Segond (tan)" data-language-autonym="Kreyòl ayisyen" data-language-local-name="Haitian Creole" class="interlanguage-link-target"><span>Kreyòl ayisyen</span></a></li><li class="interlanguage-link interwiki-gcr mw-list-item"><a href="https://gcr.wikipedia.org/wiki/S%C3%A9gonn" title="Ségonn – Guianan Creole" lang="gcr" hreflang="gcr" data-title="Ségonn" data-language-autonym="Kriyòl gwiyannen" data-language-local-name="Guianan Creole" class="interlanguage-link-target"><span>Kriyòl gwiyannen</span></a></li><li class="interlanguage-link interwiki-ku mw-list-item"><a href="https://ku.wikipedia.org/wiki/San%C3%AE" title="Sanî – Kurdish" lang="ku" hreflang="ku" data-title="Sanî" data-language-autonym="Kurdî" data-language-local-name="Kurdish" class="interlanguage-link-target"><span>Kurdî</span></a></li><li class="interlanguage-link interwiki-ky mw-list-item"><a href="https://ky.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4%D0%B0" title="Секунда – Kyrgyz" lang="ky" hreflang="ky" data-title="Секунда" data-language-autonym="Кыргызча" data-language-local-name="Kyrgyz" class="interlanguage-link-target"><span>Кыргызча</span></a></li><li class="interlanguage-link interwiki-la mw-list-item"><a href="https://la.wikipedia.org/wiki/Secundum" title="Secundum – Latin" lang="la" hreflang="la" data-title="Secundum" data-language-autonym="Latina" data-language-local-name="Latin" class="interlanguage-link-target"><span>Latina</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Sekunde" title="Sekunde – Latvian" lang="lv" hreflang="lv" data-title="Sekunde" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-lb mw-list-item"><a href="https://lb.wikipedia.org/wiki/Sekonn" title="Sekonn – Luxembourgish" lang="lb" hreflang="lb" data-title="Sekonn" data-language-autonym="Lëtzebuergesch" data-language-local-name="Luxembourgish" class="interlanguage-link-target"><span>Lëtzebuergesch</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Sekund%C4%97" title="Sekundė – Lithuanian" lang="lt" hreflang="lt" data-title="Sekundė" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-li mw-list-item"><a href="https://li.wikipedia.org/wiki/Sec%C3%B3nd" title="Secónd – Limburgish" lang="li" hreflang="li" data-title="Secónd" data-language-autonym="Limburgs" data-language-local-name="Limburgish" class="interlanguage-link-target"><span>Limburgs</span></a></li><li class="interlanguage-link interwiki-jbo mw-list-item"><a href="https://jbo.wikipedia.org/wiki/snidu" title="snidu – Lojban" lang="jbo" hreflang="jbo" data-title="snidu" data-language-autonym="La .lojban." data-language-local-name="Lojban" class="interlanguage-link-target"><span>La .lojban.</span></a></li><li class="interlanguage-link interwiki-lmo mw-list-item"><a href="https://lmo.wikipedia.org/wiki/Segond" title="Segond – Lombard" lang="lmo" hreflang="lmo" data-title="Segond" data-language-autonym="Lombard" data-language-local-name="Lombard" class="interlanguage-link-target"><span>Lombard</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/M%C3%A1sodperc" title="Másodperc – Hungarian" lang="hu" hreflang="hu" data-title="Másodperc" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-mai mw-list-item"><a href="https://mai.wikipedia.org/wiki/%E0%A4%B8%E0%A5%87%E0%A4%95%E0%A5%87%E0%A4%A3%E0%A5%8D%E0%A4%A1" title="सेकेण्ड – Maithili" lang="mai" hreflang="mai" data-title="सेकेण्ड" data-language-autonym="मैथिली" data-language-local-name="Maithili" class="interlanguage-link-target"><span>मैथिली</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4%D0%B0" title="Секунда – Macedonian" lang="mk" hreflang="mk" data-title="Секунда" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-mg mw-list-item"><a href="https://mg.wikipedia.org/wiki/Segondra" title="Segondra – Malagasy" lang="mg" hreflang="mg" data-title="Segondra" data-language-autonym="Malagasy" data-language-local-name="Malagasy" class="interlanguage-link-target"><span>Malagasy</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%9E%E0%B5%8A%E0%B4%9F%E0%B4%BF" title="ഞൊടി – Malayalam" lang="ml" hreflang="ml" data-title="ഞൊടി" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-mr mw-list-item"><a href="https://mr.wikipedia.org/wiki/%E0%A4%B8%E0%A5%87%E0%A4%95%E0%A4%82%E0%A4%A6" title="सेकंद – Marathi" lang="mr" hreflang="mr" data-title="सेकंद" data-language-autonym="मराठी" data-language-local-name="Marathi" class="interlanguage-link-target"><span>मराठी</span></a></li><li class="interlanguage-link interwiki-xmf mw-list-item"><a href="https://xmf.wikipedia.org/wiki/%E1%83%9B%E1%83%94%E1%83%A0%E1%83%A5%E1%83%90" title="მერქა – Mingrelian" lang="xmf" hreflang="xmf" data-title="მერქა" data-language-autonym="მარგალური" data-language-local-name="Mingrelian" class="interlanguage-link-target"><span>მარგალური</span></a></li><li class="interlanguage-link interwiki-arz mw-list-item"><a href="https://arz.wikipedia.org/wiki/%D8%B3%D8%A7%D9%86%D9%8A%D9%87" title="سانيه – Egyptian Arabic" lang="arz" hreflang="arz" data-title="سانيه" data-language-autonym="مصرى" data-language-local-name="Egyptian Arabic" class="interlanguage-link-target"><span>مصرى</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Saat" title="Saat – Malay" lang="ms" hreflang="ms" data-title="Saat" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-min mw-list-item"><a href="https://min.wikipedia.org/wiki/Datiak" title="Datiak – Minangkabau" lang="min" hreflang="min" data-title="Datiak" data-language-autonym="Minangkabau" data-language-local-name="Minangkabau" class="interlanguage-link-target"><span>Minangkabau</span></a></li><li class="interlanguage-link interwiki-cdo mw-list-item"><a href="https://cdo.wikipedia.org/wiki/Mi%C4%93u" title="Miēu – Mindong" lang="cdo" hreflang="cdo" data-title="Miēu" data-language-autonym="閩東語 / Mìng-dĕ̤ng-ngṳ̄" data-language-local-name="Mindong" class="interlanguage-link-target"><span>閩東語 / Mìng-dĕ̤ng-ngṳ̄</span></a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4" title="Секунд – Mongolian" lang="mn" hreflang="mn" data-title="Секунд" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target"><span>Монгол</span></a></li><li class="interlanguage-link interwiki-my mw-list-item"><a href="https://my.wikipedia.org/wiki/%E1%80%85%E1%80%80%E1%80%B9%E1%80%80%E1%80%94%E1%80%B7%E1%80%BA" title="စက္ကန့် – Burmese" lang="my" hreflang="my" data-title="စက္ကန့်" data-language-autonym="မြန်မာဘာသာ" data-language-local-name="Burmese" class="interlanguage-link-target"><span>မြန်မာဘာသာ</span></a></li><li class="interlanguage-link interwiki-fj mw-list-item"><a href="https://fj.wikipedia.org/wiki/Sekodi" title="Sekodi – Fijian" lang="fj" hreflang="fj" data-title="Sekodi" data-language-autonym="Na Vosa Vakaviti" data-language-local-name="Fijian" class="interlanguage-link-target"><span>Na Vosa Vakaviti</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Seconde" title="Seconde – Dutch" lang="nl" hreflang="nl" data-title="Seconde" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ne mw-list-item"><a href="https://ne.wikipedia.org/wiki/%E0%A4%B8%E0%A5%87%E0%A4%95%E0%A5%87%E0%A4%A8%E0%A5%8D%E0%A4%A1" title="सेकेन्ड – Nepali" lang="ne" hreflang="ne" data-title="सेकेन्ड" data-language-autonym="नेपाली" data-language-local-name="Nepali" class="interlanguage-link-target"><span>नेपाली</span></a></li><li class="interlanguage-link interwiki-ja badge-Q17437798 badge-goodarticle mw-list-item" title="good article badge"><a href="https://ja.wikipedia.org/wiki/%E7%A7%92" title="秒 – Japanese" lang="ja" hreflang="ja" data-title="秒" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-frr mw-list-item"><a href="https://frr.wikipedia.org/wiki/Sekund" title="Sekund – Northern Frisian" lang="frr" hreflang="frr" data-title="Sekund" data-language-autonym="Nordfriisk" data-language-local-name="Northern Frisian" class="interlanguage-link-target"><span>Nordfriisk</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Sekund" title="Sekund – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Sekund" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/Sekund" title="Sekund – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Sekund" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-oc mw-list-item"><a href="https://oc.wikipedia.org/wiki/Segonda" title="Segonda – Occitan" lang="oc" hreflang="oc" data-title="Segonda" data-language-autonym="Occitan" data-language-local-name="Occitan" class="interlanguage-link-target"><span>Occitan</span></a></li><li class="interlanguage-link interwiki-om mw-list-item"><a href="https://om.wikipedia.org/wiki/Sekondii" title="Sekondii – Oromo" lang="om" hreflang="om" data-title="Sekondii" data-language-autonym="Oromoo" data-language-local-name="Oromo" class="interlanguage-link-target"><span>Oromoo</span></a></li><li class="interlanguage-link interwiki-uz mw-list-item"><a href="https://uz.wikipedia.org/wiki/Soniya" title="Soniya – Uzbek" lang="uz" hreflang="uz" data-title="Soniya" data-language-autonym="Oʻzbekcha / ўзбекча" data-language-local-name="Uzbek" class="interlanguage-link-target"><span>Oʻzbekcha / ўзбекча</span></a></li><li class="interlanguage-link interwiki-pa mw-list-item"><a href="https://pa.wikipedia.org/wiki/%E0%A8%B8%E0%A8%95%E0%A8%BF%E0%A9%B0%E0%A8%9F" title="ਸਕਿੰਟ – Punjabi" lang="pa" hreflang="pa" data-title="ਸਕਿੰਟ" data-language-autonym="ਪੰਜਾਬੀ" data-language-local-name="Punjabi" class="interlanguage-link-target"><span>ਪੰਜਾਬੀ</span></a></li><li class="interlanguage-link interwiki-pnb mw-list-item"><a href="https://pnb.wikipedia.org/wiki/%D8%B3%DA%A9%D9%86%D9%B9" title="سکنٹ – Western Punjabi" lang="pnb" hreflang="pnb" data-title="سکنٹ" data-language-autonym="پنجابی" data-language-local-name="Western Punjabi" class="interlanguage-link-target"><span>پنجابی</span></a></li><li class="interlanguage-link interwiki-ps mw-list-item"><a href="https://ps.wikipedia.org/wiki/%D8%AB%D8%A7%D9%86%D9%8A%D9%87" title="ثانيه – Pashto" lang="ps" hreflang="ps" data-title="ثانيه" data-language-autonym="پښتو" data-language-local-name="Pashto" class="interlanguage-link-target"><span>پښتو</span></a></li><li class="interlanguage-link interwiki-jam mw-list-item"><a href="https://jam.wikipedia.org/wiki/Sekan" title="Sekan – Jamaican Creole English" lang="jam" hreflang="jam" data-title="Sekan" data-language-autonym="Patois" data-language-local-name="Jamaican Creole English" class="interlanguage-link-target"><span>Patois</span></a></li><li class="interlanguage-link interwiki-pms mw-list-item"><a href="https://pms.wikipedia.org/wiki/Second" title="Second – Piedmontese" lang="pms" hreflang="pms" data-title="Second" data-language-autonym="Piemontèis" data-language-local-name="Piedmontese" class="interlanguage-link-target"><span>Piemontèis</span></a></li><li class="interlanguage-link interwiki-nds mw-list-item"><a href="https://nds.wikipedia.org/wiki/Sekunn" title="Sekunn – Low German" lang="nds" hreflang="nds" data-title="Sekunn" data-language-autonym="Plattdüütsch" data-language-local-name="Low German" class="interlanguage-link-target"><span>Plattdüütsch</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Sekunda" title="Sekunda – Polish" lang="pl" hreflang="pl" data-title="Sekunda" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Segundo" title="Segundo – Portuguese" lang="pt" hreflang="pt" data-title="Segundo" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-crh mw-list-item"><a href="https://crh.wikipedia.org/wiki/Saniye" title="Saniye – Crimean Tatar" lang="crh" hreflang="crh" data-title="Saniye" data-language-autonym="Qırımtatarca" data-language-local-name="Crimean Tatar" class="interlanguage-link-target"><span>Qırımtatarca</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Secund%C4%83" title="Secundă – Romanian" lang="ro" hreflang="ro" data-title="Secundă" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-qu mw-list-item"><a href="https://qu.wikipedia.org/wiki/Sikunthu" title="Sikunthu – Quechua" lang="qu" hreflang="qu" data-title="Sikunthu" data-language-autonym="Runa Simi" data-language-local-name="Quechua" class="interlanguage-link-target"><span>Runa Simi</span></a></li><li class="interlanguage-link interwiki-rue mw-list-item"><a href="https://rue.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4%D0%B0" title="Секунда – Rusyn" lang="rue" hreflang="rue" data-title="Секунда" data-language-autonym="Русиньскый" data-language-local-name="Rusyn" class="interlanguage-link-target"><span>Русиньскый</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4%D0%B0" title="Секунда – Russian" lang="ru" hreflang="ru" data-title="Секунда" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sah mw-list-item"><a href="https://sah.wikipedia.org/wiki/%D0%A1%D3%A9%D0%BA%D2%AF%D2%AF%D0%BD%D0%B4%D1%8D" title="Сөкүүндэ – Yakut" lang="sah" hreflang="sah" data-title="Сөкүүндэ" data-language-autonym="Саха тыла" data-language-local-name="Yakut" class="interlanguage-link-target"><span>Саха тыла</span></a></li><li class="interlanguage-link interwiki-sat mw-list-item"><a href="https://sat.wikipedia.org/wiki/%E1%B1%B4%E1%B1%A4%E1%B1%AF%E1%B1%A4%E1%B1%A1" title="ᱴᱤᱯᱤᱡ – Santali" lang="sat" hreflang="sat" data-title="ᱴᱤᱯᱤᱡ" data-language-autonym="ᱥᱟᱱᱛᱟᱲᱤ" data-language-local-name="Santali" class="interlanguage-link-target"><span>ᱥᱟᱱᱛᱟᱲᱤ</span></a></li><li class="interlanguage-link interwiki-sc mw-list-item"><a href="https://sc.wikipedia.org/wiki/Segundu" title="Segundu – Sardinian" lang="sc" hreflang="sc" data-title="Segundu" data-language-autonym="Sardu" data-language-local-name="Sardinian" class="interlanguage-link-target"><span>Sardu</span></a></li><li class="interlanguage-link interwiki-sco mw-list-item"><a href="https://sco.wikipedia.org/wiki/Seicont" title="Seicont – Scots" lang="sco" hreflang="sco" data-title="Seicont" data-language-autonym="Scots" data-language-local-name="Scots" class="interlanguage-link-target"><span>Scots</span></a></li><li class="interlanguage-link interwiki-nso mw-list-item"><a href="https://nso.wikipedia.org/wiki/Motsotswana" title="Motsotswana – Northern Sotho" lang="nso" hreflang="nso" data-title="Motsotswana" data-language-autonym="Sesotho sa Leboa" data-language-local-name="Northern Sotho" class="interlanguage-link-target"><span>Sesotho sa Leboa</span></a></li><li class="interlanguage-link interwiki-sq mw-list-item"><a href="https://sq.wikipedia.org/wiki/Sekonda" title="Sekonda – Albanian" lang="sq" hreflang="sq" data-title="Sekonda" data-language-autonym="Shqip" data-language-local-name="Albanian" class="interlanguage-link-target"><span>Shqip</span></a></li><li class="interlanguage-link interwiki-si mw-list-item"><a href="https://si.wikipedia.org/wiki/%E0%B6%AD%E0%B6%AD%E0%B7%8A%E0%B6%B4%E0%B6%BB%E0%B6%BA" title="තත්පරය – Sinhala" lang="si" hreflang="si" data-title="තත්පරය" data-language-autonym="සිංහල" data-language-local-name="Sinhala" class="interlanguage-link-target"><span>සිංහල</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Second" title="Second – Simple English" lang="en-simple" hreflang="en-simple" data-title="Second" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sd mw-list-item"><a href="https://sd.wikipedia.org/wiki/%D8%B3%D9%8A%DA%AA%D9%86%DA%8A" title="سيڪنڊ – Sindhi" lang="sd" hreflang="sd" data-title="سيڪنڊ" data-language-autonym="سنڌي" data-language-local-name="Sindhi" class="interlanguage-link-target"><span>سنڌي</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Sekunda" title="Sekunda – Slovak" lang="sk" hreflang="sk" data-title="Sekunda" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Sekunda" title="Sekunda – Slovenian" lang="sl" hreflang="sl" data-title="Sekunda" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-cu mw-list-item"><a href="https://cu.wikipedia.org/wiki/%D0%94%D1%94%D1%B5%D1%82%D1%94%D1%80%D0%BE%D0%BB%D1%94%D0%BF%D1%82%D0%BE" title="Дєѵтєролєпто – Church Slavic" lang="cu" hreflang="cu" data-title="Дєѵтєролєпто" data-language-autonym="Словѣньскъ / ⰔⰎⰑⰂⰡⰐⰠⰔⰍⰟ" data-language-local-name="Church Slavic" class="interlanguage-link-target"><span>Словѣньскъ / ⰔⰎⰑⰂⰡⰐⰠⰔⰍⰟ</span></a></li><li class="interlanguage-link interwiki-szl mw-list-item"><a href="https://szl.wikipedia.org/wiki/Sek%C5%8Dnda" title="Sekōnda – Silesian" lang="szl" hreflang="szl" data-title="Sekōnda" data-language-autonym="Ślůnski" data-language-local-name="Silesian" class="interlanguage-link-target"><span>Ślůnski</span></a></li><li class="interlanguage-link interwiki-so mw-list-item"><a href="https://so.wikipedia.org/wiki/Ilbiriqsi" title="Ilbiriqsi – Somali" lang="so" hreflang="so" data-title="Ilbiriqsi" data-language-autonym="Soomaaliga" data-language-local-name="Somali" class="interlanguage-link-target"><span>Soomaaliga</span></a></li><li class="interlanguage-link interwiki-ckb mw-list-item"><a href="https://ckb.wikipedia.org/wiki/%DA%86%D8%B1%DA%A9%DB%95" title="چرکە – Central Kurdish" lang="ckb" hreflang="ckb" data-title="چرکە" data-language-autonym="کوردی" data-language-local-name="Central Kurdish" class="interlanguage-link-target"><span>کوردی</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4" title="Секунд – Serbian" lang="sr" hreflang="sr" data-title="Секунд" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/Sekund" title="Sekund – Serbo-Croatian" lang="sh" hreflang="sh" data-title="Sekund" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-su mw-list-item"><a href="https://su.wikipedia.org/wiki/Detik" title="Detik – Sundanese" lang="su" hreflang="su" data-title="Detik" data-language-autonym="Sunda" data-language-local-name="Sundanese" class="interlanguage-link-target"><span>Sunda</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Sekunti" title="Sekunti – Finnish" lang="fi" hreflang="fi" data-title="Sekunti" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Sekund" title="Sekund – Swedish" lang="sv" hreflang="sv" data-title="Sekund" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-tl mw-list-item"><a href="https://tl.wikipedia.org/wiki/Segundo" title="Segundo – Tagalog" lang="tl" hreflang="tl" data-title="Segundo" data-language-autonym="Tagalog" data-language-local-name="Tagalog" class="interlanguage-link-target"><span>Tagalog</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%A8%E0%AF%8A%E0%AE%9F%E0%AE%BF_(%E0%AE%95%E0%AE%BE%E0%AE%B2_%E0%AE%85%E0%AE%B3%E0%AE%B5%E0%AF%81)" title="நொடி (கால அளவு) – Tamil" lang="ta" hreflang="ta" data-title="நொடி (கால அளவு)" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-kab mw-list-item"><a href="https://kab.wikipedia.org/wiki/Tasint" title="Tasint – Kabyle" lang="kab" hreflang="kab" data-title="Tasint" data-language-autonym="Taqbaylit" data-language-local-name="Kabyle" class="interlanguage-link-target"><span>Taqbaylit</span></a></li><li class="interlanguage-link interwiki-roa-tara mw-list-item"><a href="https://roa-tara.wikipedia.org/wiki/Seconne" title="Seconne – Tarantino" lang="nap-x-tara" hreflang="nap-x-tara" data-title="Seconne" data-language-autonym="Tarandíne" data-language-local-name="Tarantino" class="interlanguage-link-target"><span>Tarandíne</span></a></li><li class="interlanguage-link interwiki-tt mw-list-item"><a href="https://tt.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4" title="Секунд – Tatar" lang="tt" hreflang="tt" data-title="Секунд" data-language-autonym="Татарча / tatarça" data-language-local-name="Tatar" class="interlanguage-link-target"><span>Татарча / tatarça</span></a></li><li class="interlanguage-link interwiki-te mw-list-item"><a href="https://te.wikipedia.org/wiki/%E0%B0%B8%E0%B1%86%E0%B0%95%E0%B0%82%E0%B0%A1%E0%B1%81" title="సెకండు – Telugu" lang="te" hreflang="te" data-title="సెకండు" data-language-autonym="తెలుగు" data-language-local-name="Telugu" class="interlanguage-link-target"><span>తెలుగు</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%A7%E0%B8%B4%E0%B8%99%E0%B8%B2%E0%B8%97%E0%B8%B5" title="วินาที – Thai" lang="th" hreflang="th" data-title="วินาที" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tg mw-list-item"><a href="https://tg.wikipedia.org/wiki/%D0%A1%D0%BE%D0%BD%D0%B8%D1%8F" title="Сония – Tajik" lang="tg" hreflang="tg" data-title="Сония" data-language-autonym="Тоҷикӣ" data-language-local-name="Tajik" class="interlanguage-link-target"><span>Тоҷикӣ</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Saniye" title="Saniye – Turkish" lang="tr" hreflang="tr" data-title="Saniye" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%83%D0%BD%D0%B4%D0%B0" title="Секунда – Ukrainian" lang="uk" hreflang="uk" data-title="Секунда" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-ur mw-list-item"><a href="https://ur.wikipedia.org/wiki/%D8%AB%D8%A7%D9%86%DB%8C%DB%81" title="ثانیہ – Urdu" lang="ur" hreflang="ur" data-title="ثانیہ" data-language-autonym="اردو" data-language-local-name="Urdu" class="interlanguage-link-target"><span>اردو</span></a></li><li class="interlanguage-link interwiki-za mw-list-item"><a href="https://za.wikipedia.org/wiki/Miux" title="Miux – Zhuang" lang="za" hreflang="za" data-title="Miux" data-language-autonym="Vahcuengh" data-language-local-name="Zhuang" class="interlanguage-link-target"><span>Vahcuengh</span></a></li><li class="interlanguage-link interwiki-vep mw-list-item"><a href="https://vep.wikipedia.org/wiki/Sekund" title="Sekund – Veps" lang="vep" hreflang="vep" data-title="Sekund" data-language-autonym="Vepsän kel’" data-language-local-name="Veps" class="interlanguage-link-target"><span>Vepsän kel’</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/Gi%C3%A2y" title="Giây – Vietnamese" lang="vi" hreflang="vi" data-title="Giây" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-wa mw-list-item"><a href="https://wa.wikipedia.org/wiki/Sigonde" title="Sigonde – Walloon" lang="wa" hreflang="wa" data-title="Sigonde" data-language-autonym="Walon" data-language-local-name="Walloon" class="interlanguage-link-target"><span>Walon</span></a></li><li class="interlanguage-link interwiki-zh-classical mw-list-item"><a href="https://zh-classical.wikipedia.org/wiki/%E7%A7%92" title="秒 – Literary Chinese" lang="lzh" hreflang="lzh" data-title="秒" data-language-autonym="文言" data-language-local-name="Literary Chinese" class="interlanguage-link-target"><span>文言</span></a></li><li class="interlanguage-link interwiki-vls mw-list-item"><a href="https://vls.wikipedia.org/wiki/Seconde" title="Seconde – West Flemish" lang="vls" hreflang="vls" data-title="Seconde" data-language-autonym="West-Vlams" data-language-local-name="West Flemish" class="interlanguage-link-target"><span>West-Vlams</span></a></li><li class="interlanguage-link interwiki-war mw-list-item"><a href="https://war.wikipedia.org/wiki/Segundo" title="Segundo – Waray" lang="war" hreflang="war" data-title="Segundo" data-language-autonym="Winaray" data-language-local-name="Waray" class="interlanguage-link-target"><span>Winaray</span></a></li><li class="interlanguage-link interwiki-wo mw-list-item"><a href="https://wo.wikipedia.org/wiki/Saa" title="Saa – Wolof" lang="wo" hreflang="wo" data-title="Saa" data-language-autonym="Wolof" data-language-local-name="Wolof" class="interlanguage-link-target"><span>Wolof</span></a></li><li class="interlanguage-link interwiki-wuu mw-list-item"><a href="https://wuu.wikipedia.org/wiki/%E7%A7%92" title="秒 – Wu" lang="wuu" hreflang="wuu" data-title="秒" data-language-autonym="吴语" data-language-local-name="Wu" class="interlanguage-link-target"><span>吴语</span></a></li><li class="interlanguage-link interwiki-yi mw-list-item"><a href="https://yi.wikipedia.org/wiki/%D7%A1%D7%A2%D7%A7%D7%95%D7%A0%D7%93%D7%A2" title="סעקונדע – Yiddish" lang="yi" hreflang="yi" data-title="סעקונדע" data-language-autonym="ייִדיש" data-language-local-name="Yiddish" class="interlanguage-link-target"><span>ייִדיש</span></a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/%E7%A7%92%E9%90%98" title="秒鐘 – Cantonese" lang="yue" hreflang="yue" data-title="秒鐘" data-language-autonym="粵語" data-language-local-name="Cantonese" class="interlanguage-link-target"><span>粵語</span></a></li><li class="interlanguage-link interwiki-bat-smg mw-list-item"><a href="https://bat-smg.wikipedia.org/wiki/Sekond%C4%97" title="Sekondė – Samogitian" lang="sgs" hreflang="sgs" data-title="Sekondė" data-language-autonym="Žemaitėška" data-language-local-name="Samogitian" class="interlanguage-link-target"><span>Žemaitėška</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E7%A7%92" title="秒 – Chinese" lang="zh" hreflang="zh" data-title="秒" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li><li class="interlanguage-link interwiki-bew mw-list-item"><a href="https://bew.wikipedia.org/wiki/Sekon" title="Sekon – Betawi" lang="bew" hreflang="bew" data-title="Sekon" data-language-autonym="Betawi" data-language-local-name="Betawi" class="interlanguage-link-target"><span>Betawi</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q11574#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div id="p-associated-pages" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-associated-pages" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-nstab-main" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/Second" title="View the content page [c]" accesskey="c"><span>Article</span></a></li><li id="ca-talk" class="vector-tab-noicon mw-list-item"><a href="/wiki/Talk:Second" rel="discussion" title="Discuss improvements to the content page [t]" accesskey="t"><span>Talk</span></a></li> </ul> </div> </div> <div id="vector-variants-dropdown" class="vector-dropdown emptyPortlet" > <input type="checkbox" id="vector-variants-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-variants-dropdown" class="vector-dropdown-checkbox " aria-label="Change language variant" > <label id="vector-variants-dropdown-label" for="vector-variants-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span class="vector-dropdown-label-text">English</span> </label> <div class="vector-dropdown-content"> <div id="p-variants" class="vector-menu mw-portlet mw-portlet-variants emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> </div> </div> </nav> </div> <div id="right-navigation" class="vector-collapsible"> <nav aria-label="Views"> <div id="p-views" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-views" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-view" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/Second"><span>Read</span></a></li><li id="ca-edit" class="vector-tab-noicon mw-list-item"><a href="/w/index.php?title=Second&action=edit" title="Edit this page [e]" accesskey="e"><span>Edit</span></a></li><li id="ca-history" class="vector-tab-noicon mw-list-item"><a href="/w/index.php?title=Second&action=history" title="Past revisions of this page [h]" accesskey="h"><span>View history</span></a></li> </ul> </div> </div> </nav> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-dropdown" class="vector-dropdown vector-page-tools-dropdown" > <input type="checkbox" id="vector-page-tools-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-tools-dropdown" class="vector-dropdown-checkbox " aria-label="Tools" > <label id="vector-page-tools-dropdown-label" for="vector-page-tools-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span class="vector-dropdown-label-text">Tools</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-tools-unpinned-container" class="vector-unpinned-container"> <div id="vector-page-tools" class="vector-page-tools vector-pinnable-element"> <div class="vector-pinnable-header vector-page-tools-pinnable-header vector-pinnable-header-unpinned" data-feature-name="page-tools-pinned" data-pinnable-element-id="vector-page-tools" data-pinned-container-id="vector-page-tools-pinned-container" data-unpinned-container-id="vector-page-tools-unpinned-container" > <div class="vector-pinnable-header-label">Tools</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-page-tools.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-page-tools.unpin">hide</button> </div> <div id="p-cactions" class="vector-menu mw-portlet mw-portlet-cactions emptyPortlet vector-has-collapsible-items" title="More options" > <div class="vector-menu-heading"> Actions </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-more-view" class="selected vector-more-collapsible-item mw-list-item"><a href="/wiki/Second"><span>Read</span></a></li><li id="ca-more-edit" class="vector-more-collapsible-item mw-list-item"><a href="/w/index.php?title=Second&action=edit" title="Edit this page [e]" accesskey="e"><span>Edit</span></a></li><li id="ca-more-history" class="vector-more-collapsible-item mw-list-item"><a href="/w/index.php?title=Second&action=history"><span>View history</span></a></li> </ul> </div> </div> <div id="p-tb" class="vector-menu mw-portlet mw-portlet-tb" > <div class="vector-menu-heading"> General </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="t-whatlinkshere" class="mw-list-item"><a href="/wiki/Special:WhatLinksHere/Second" title="List of all English Wikipedia pages containing links to this page [j]" accesskey="j"><span>What links here</span></a></li><li id="t-recentchangeslinked" class="mw-list-item"><a href="/wiki/Special:RecentChangesLinked/Second" rel="nofollow" title="Recent changes in pages linked from this page [k]" accesskey="k"><span>Related changes</span></a></li><li id="t-upload" class="mw-list-item"><a href="/wiki/Wikipedia:File_Upload_Wizard" title="Upload files [u]" accesskey="u"><span>Upload file</span></a></li><li id="t-specialpages" class="mw-list-item"><a href="/wiki/Special:SpecialPages" title="A list of all special pages [q]" accesskey="q"><span>Special pages</span></a></li><li id="t-permalink" class="mw-list-item"><a href="/w/index.php?title=Second&oldid=1256553341" title="Permanent link to this revision of this page"><span>Permanent link</span></a></li><li id="t-info" class="mw-list-item"><a href="/w/index.php?title=Second&action=info" title="More information about this page"><span>Page information</span></a></li><li id="t-cite" class="mw-list-item"><a href="/w/index.php?title=Special:CiteThisPage&page=Second&id=1256553341&wpFormIdentifier=titleform" title="Information on how to cite this page"><span>Cite this page</span></a></li><li id="t-urlshortener" class="mw-list-item"><a href="/w/index.php?title=Special:UrlShortener&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSecond"><span>Get shortened URL</span></a></li><li id="t-urlshortener-qrcode" class="mw-list-item"><a href="/w/index.php?title=Special:QrCode&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSecond"><span>Download QR code</span></a></li> </ul> </div> </div> <div id="p-coll-print_export" class="vector-menu mw-portlet mw-portlet-coll-print_export" > <div class="vector-menu-heading"> Print/export </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="coll-download-as-rl" class="mw-list-item"><a href="/w/index.php?title=Special:DownloadAsPdf&page=Second&action=show-download-screen" title="Download this page as a PDF file"><span>Download as PDF</span></a></li><li id="t-print" class="mw-list-item"><a href="/w/index.php?title=Second&printable=yes" title="Printable version of this page [p]" accesskey="p"><span>Printable version</span></a></li> </ul> </div> </div> <div id="p-wikibase-otherprojects" class="vector-menu mw-portlet mw-portlet-wikibase-otherprojects" > <div class="vector-menu-heading"> In other projects </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="wb-otherproject-link wb-otherproject-commons mw-list-item"><a href="https://commons.wikimedia.org/wiki/Second" hreflang="en"><span>Wikimedia Commons</span></a></li><li id="t-wikibase" class="wb-otherproject-link wb-otherproject-wikibase-dataitem mw-list-item"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q11574" title="Structured data on this page hosted by Wikidata [g]" accesskey="g"><span>Wikidata item</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> </div> </div> </div> <div class="vector-column-end"> <div class="vector-sticky-pinned-container"> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-pinned-container" class="vector-pinned-container"> </div> </nav> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-pinned-container" class="vector-pinned-container"> <div id="vector-appearance" class="vector-appearance vector-pinnable-element"> <div class="vector-pinnable-header vector-appearance-pinnable-header vector-pinnable-header-pinned" data-feature-name="appearance-pinned" data-pinnable-element-id="vector-appearance" data-pinned-container-id="vector-appearance-pinned-container" data-unpinned-container-id="vector-appearance-unpinned-container" > <div class="vector-pinnable-header-label">Appearance</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-appearance.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-appearance.unpin">hide</button> </div> </div> </div> </nav> </div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">SI unit of time</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">This article is about the unit of clock time. For other uses, see <a href="/wiki/Second_(disambiguation)" class="mw-disambig" title="Second (disambiguation)">Second (disambiguation)</a>.</div> <p class="mw-empty-elt"> </p> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox ib-unit"><tbody><tr><th colspan="2" class="infobox-above">second</th></tr><tr><td colspan="2" class="infobox-image notheme" style="background-color: #f8f9fa;"><span class="mw-default-size" typeof="mw:File/Frameless"><a href="/wiki/File:Clock-pendulum.gif" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/15/Clock-pendulum.gif/220px-Clock-pendulum.gif" decoding="async" width="220" height="417" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/15/Clock-pendulum.gif/330px-Clock-pendulum.gif 1.5x, //upload.wikimedia.org/wikipedia/commons/1/15/Clock-pendulum.gif 2x" data-file-width="353" data-file-height="669" /></a></span><div class="infobox-caption">A pendulum-governed <a href="/wiki/Escapement" title="Escapement">escapement</a> of a clock, ticking every second</div></td></tr><tr><th colspan="2" class="infobox-header">General information</th></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/System_of_units_of_measurement" title="System of units of measurement">Unit system</a></th><td class="infobox-data"><a href="/wiki/SI" class="mw-redirect" title="SI">SI</a></td></tr><tr><th scope="row" class="infobox-label">Unit of</th><td class="infobox-data"><a href="/wiki/Time" title="Time">time</a></td></tr><tr><th scope="row" class="infobox-label">Symbol</th><td class="infobox-data">s</td></tr></tbody></table><style data-mw-deduplicate="TemplateStyles:r1236303919">@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-has-images-with-white-backgrounds img{background:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-has-images-with-white-backgrounds img{background:white}}</style> <p>The <b>second</b> (symbol: <b>s</b>) is a unit of <a href="/wiki/Time_in_physics" title="Time in physics">time</a>, historically defined as <style data-mw-deduplicate="TemplateStyles:r1154941027">.mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="frac"><span class="num">1</span>⁄<span class="den">86400</span></span> of a <a href="/wiki/Day" title="Day">day</a> – this factor derived from the division of the day first into 24 <a href="/wiki/Hour" title="Hour">hours</a>, then to 60 <a href="/wiki/Minute" title="Minute">minutes</a> and finally to 60 seconds each (24 × 60 × 60 = 86400). </p><p> The current and formal definition in the <a href="/wiki/International_System_of_Units" title="International System of Units">International System of Units</a> (SI) is more precise:</p><blockquote><p>The second [...] is defined by taking the fixed numerical value of the caesium frequency, Δ<i>ν</i><sub>Cs</sub>, the unperturbed <a href="/wiki/Ground_state" title="Ground state">ground-state</a> <a href="/wiki/Hyperfine_structure" title="Hyperfine structure">hyperfine</a> transition frequency of the <a href="/wiki/Caesium-133" class="mw-redirect" title="Caesium-133">caesium 133</a> atom, to be <span style="white-space:nowrap">9<span style="margin-left:0.25em">192</span><span style="margin-left:0.25em">631</span><span style="margin-left:0.25em">770</span></span> when expressed in the unit <a href="/wiki/Hertz" title="Hertz">Hz</a>, which is equal to s<sup>−1</sup>.<sup id="cite_ref-BIPM9_1-0" class="reference"><a href="#cite_note-BIPM9-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup></p></blockquote> <p>This current definition was adopted in 1967 when it became feasible to define the second based on fundamental properties of nature with <a href="/wiki/Caesium_clock" class="mw-redirect" title="Caesium clock">caesium clocks</a>.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> Because the speed of Earth's rotation varies and is slowing <a href="/wiki/%CE%94T_(timekeeping)" title="ΔT (timekeeping)">ever so slightly</a>, a <a href="/wiki/Leap_second" title="Leap second">leap second</a> is added at irregular intervals to <a href="/wiki/Civil_time" title="Civil time">civil time</a><sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>nb 1<span class="cite-bracket">]</span></a></sup> to keep clocks in sync with Earth's rotation. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Etymology">Etymology</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=1" title="Edit section: Etymology"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>"Minute" comes from the Latin <span title="Latin-language text"><i lang="la">pars minuta prima</i></span>, meaning "first small part" i.e. first division of the hour - dividing into sixty, and "second" comes from the <span title="Latin-language text"><i lang="la">pars minuta secunda</i></span>, "second small part", dividing again into sixty.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Uses">Uses</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=2" title="Edit section: Uses"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Analog_clock" class="mw-redirect" title="Analog clock">Analog clocks</a> and <a href="/wiki/Watch" title="Watch">watches</a> often have sixty tick marks on their faces, representing seconds (and minutes), and a "second hand" to mark the passage of time in seconds. Digital clocks and watches often have a two-digit seconds counter. </p><p><a href="/wiki/SI_prefix" class="mw-redirect" title="SI prefix">SI prefixes</a> are frequently combined with the word <i>second</i> to denote subdivisions of the second: milliseconds (thousandths), microseconds (millionths), nanoseconds (billionths), and sometimes smaller units of a second. Multiples of seconds are usually counted in hours and minutes. Though SI prefixes may also be used to form multiples of the second such as kiloseconds (thousands of seconds), such units are rarely used in practice. An everyday experience with small fractions of a second is a 1-gigahertz microprocessor that has a cycle time of 1 nanosecond. Camera <a href="/wiki/Shutter_speed" title="Shutter speed">shutter speeds</a> are often expressed in fractions of a second, such as <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">1</span>⁄<span class="den">30</span></span> second or <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">1</span>⁄<span class="den">1000</span></span> second. </p><p><a href="/wiki/Sexagesimal" title="Sexagesimal">Sexagesimal</a> divisions of the day from a calendar based on astronomical observation have existed since the third millennium BC, though they were not seconds as we know them today.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Small divisions of time could not be measured back then, so such divisions were mathematically derived. The first timekeepers that could count seconds accurately were pendulum clocks invented in the 17th century. Starting in the 1950s, <a href="/wiki/Atomic_clock" title="Atomic clock">atomic clocks</a> became better timekeepers than Earth's rotation, and they continue to set the standard today. </p> <div class="mw-heading mw-heading2"><h2 id="Clocks_and_solar_time">Clocks and solar time</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=3" title="Edit section: Clocks and solar time"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A mechanical clock, which does not depend on measuring the relative rotational position of the Earth, keeps uniform time called <i>mean time</i>, within whatever accuracy is intrinsic to it. That means that every second, minute and every other division of time counted by the clock has the same duration as any other identical division of time. But a <a href="/wiki/Sundial" title="Sundial">sundial</a>, which measures the relative position of the Sun in the sky called <i>apparent time</i>, does not keep uniform time. The time kept by a sundial varies by time of year, meaning that seconds, minutes and every other division of time is a different duration at different times of the year. The time of day measured with mean time versus apparent time may differ by as much as 15 minutes, but a single day differs from the next by only a small amount; 15 minutes is a cumulative difference over a part of the year. The effect is due chiefly to the obliqueness of Earth's axis with respect to its <a href="/wiki/Orbit" title="Orbit">orbit</a> around the Sun. </p><p>The difference between apparent solar time and mean time was recognized by astronomers since antiquity, but prior to the invention of accurate mechanical clocks in the mid-17th century, sundials were the only reliable timepieces, and apparent solar time was the only generally accepted standard. </p> <div class="mw-heading mw-heading2"><h2 id="Events_and_units_of_time_in_seconds">Events and units of time in seconds</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=4" title="Edit section: Events and units of time in seconds"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Fractions of a second are usually denoted in decimal notation, for example 2.01 seconds, or two and one hundredth seconds. Multiples of seconds are usually expressed as minutes and seconds, or hours, minutes and seconds of clock time, separated by colons, such as 11:23:24, or 45:23 (the latter notation can give rise to ambiguity, because the same notation is used to denote hours and minutes). It rarely makes sense to express longer periods of time like hours or days in seconds, because they are awkwardly large numbers. For the metric unit of second, there are <a href="/wiki/Metric_prefix" title="Metric prefix">decimal prefixes</a> representing 10<sup>−30</sup> to 10<sup>30</sup> seconds. </p><p>Some common units of time in seconds are: a minute is 60 seconds; an hour is 3,600 seconds; a day is 86,400 seconds; a week is 604,800 seconds; a year (other than <a href="/wiki/Leap_year" title="Leap year">leap years</a>) is 31,536,000 seconds; and a (<a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian</a>) century averages 3,155,695,200 seconds; with all of the above excluding any possible <a href="/wiki/Leap_second" title="Leap second">leap seconds</a>. In astronomy, a <a href="/wiki/Julian_year_(astronomy)" title="Julian year (astronomy)">Julian year</a> is precisely 31,557,600 seconds. </p><p>Some common events in seconds are: a stone falls about 4.9 meters from rest in one second; a pendulum of length about one meter has a swing of one second, so pendulum clocks have pendulums about a meter long; the fastest human sprinters run 10 meters in a second; an ocean wave in deep water travels about 23 meters in one second; sound travels about 343 meters in one second in air; light takes 1.3 seconds to reach Earth from the surface of the Moon, a distance of 384,400 kilometers. </p> <div class="mw-heading mw-heading2"><h2 id="Other_units_incorporating_seconds">Other units incorporating seconds</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=5" title="Edit section: Other units incorporating seconds"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A second is directly part of other units, such as <a href="/wiki/Frequency" title="Frequency">frequency</a> measured in <a href="/wiki/Hertz" title="Hertz">hertz</a> (<a href="/wiki/Inverse_seconds" class="mw-redirect" title="Inverse seconds">inverse seconds</a> or s<sup>−1</sup>), <a href="/wiki/Speed" title="Speed">speed</a> in meters per second, and <a href="/wiki/Acceleration" title="Acceleration">acceleration</a> in meters per second squared. The metric system unit <a href="/wiki/Becquerel" title="Becquerel">becquerel</a>, a measure of radioactive decay, is measured in inverse seconds and higher powers of second are involved in <a href="/wiki/Fourth,_fifth,_and_sixth_derivatives_of_position" title="Fourth, fifth, and sixth derivatives of position">derivatives of acceleration</a> such as <a href="/wiki/Jerk_(physics)" title="Jerk (physics)">jerk</a>. Though many derivative units for everyday things are reported in terms of larger units of time, not seconds, they are ultimately defined in terms of the SI second; this includes time expressed in hours and minutes, velocity of a car in kilometers per hour or miles per hour, kilowatt hours of electricity usage, and speed of a turntable in rotations per minute. </p><p>Moreover, most other <a href="/wiki/SI_base_units" class="mw-redirect" title="SI base units">SI base units</a> are defined by their relationship to the second: the <a href="/wiki/Meter" class="mw-redirect" title="Meter">meter</a> is defined by setting the <a href="/wiki/Speed_of_light" title="Speed of light">speed of light</a> (in vacuum) to be 299 792 458 m/s, exactly; definitions of the SI base units <a href="/wiki/Kilogram" title="Kilogram">kilogram</a>, <a href="/wiki/Ampere" title="Ampere">ampere</a>, <a href="/wiki/Kelvin" title="Kelvin">kelvin</a>, and <a href="/wiki/Candela" title="Candela">candela</a> also depend on the second. The only base unit whose definition does not depend on the second is the <a href="/wiki/Mole_(unit)" title="Mole (unit)">mole</a>, and only two of the 22 named derived units, <a href="/wiki/Radian" title="Radian">radian</a> and <a href="/wiki/Steradian" title="Steradian">steradian</a>, do not depend on the second either. </p> <div class="mw-heading mw-heading2"><h2 id="Timekeeping_standards">Timekeeping standards</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=6" title="Edit section: Timekeeping standards"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Time_standard" title="Time standard">Time standard</a></div> <p>A set of atomic clocks throughout the world keeps time by consensus: the clocks "vote" on the correct time, and all voting clocks are steered to agree with the consensus, which is called <a href="/wiki/International_Atomic_Time" title="International Atomic Time">International Atomic Time</a> (TAI). TAI "ticks" atomic seconds.<sup id="cite_ref-McCarthy_2009_6-0" class="reference"><a href="#cite_note-McCarthy_2009-6"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 207–218">: 207–218 </span></sup> </p><p>Civil time is defined to agree with the rotation of the Earth. The international standard for timekeeping is <a href="/wiki/Coordinated_Universal_Time" title="Coordinated Universal Time">Coordinated Universal Time</a> (UTC). This time scale "ticks" the same atomic seconds as TAI, but inserts or omits <a href="/wiki/Leap_second" title="Leap second">leap seconds</a> as necessary to correct for variations in the rate of rotation of the Earth.<sup id="cite_ref-McCarthy_2009_6-1" class="reference"><a href="#cite_note-McCarthy_2009-6"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 16–17, 207">: 16–17, 207 </span></sup> </p><p>A time scale in which the seconds are not exactly equal to atomic seconds is UT1, a form of <a href="/wiki/Universal_time" class="mw-redirect" title="Universal time">universal time</a>. UT1 is defined by the rotation of the Earth with respect to the Sun, and does not contain any leap seconds.<sup id="cite_ref-McCarthy_2009_6-2" class="reference"><a href="#cite_note-McCarthy_2009-6"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 68, 232">: 68, 232 </span></sup> UT1 always differs from UTC by less than a second. </p> <div class="mw-heading mw-heading3"><h3 id="Optical_lattice_clock">Optical lattice clock</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=7" title="Edit section: Optical lattice clock"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Optical_clock" title="Optical clock">Optical clock</a></div> <p>While they are not yet part of any timekeeping standard, optical lattice clocks with frequencies in the visible light spectrum now exist and are the most accurate timekeepers of all. A <a href="/wiki/Strontium" title="Strontium">strontium</a> clock with frequency 430 <a href="/wiki/Terahertz_(unit)" class="mw-redirect" title="Terahertz (unit)">THz</a>, in the red range of visible light, during the 2010s held the accuracy record: it gains or loses less than a second in 15 billion years, which is longer than the estimated age of the universe. Such a clock can measure a change in its elevation of as little as 2 cm by the change in its rate due to <a href="/wiki/Gravitational_time_dilation" title="Gravitational time dilation">gravitational time dilation</a>.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="History_of_definition">History of definition</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=8" title="Edit section: History of definition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/History_of_timekeeping_devices" title="History of timekeeping devices">History of timekeeping devices</a></div> <p>There have only ever been three definitions of the second: as a fraction of the day, as a fraction of an extrapolated year, and as the microwave frequency of a <a href="/wiki/Caesium" title="Caesium">caesium</a> atomic clock, which have each realized a sexagesimal division of the day from ancient astronomical calendars. </p> <div class="mw-heading mw-heading3"><h3 id="Sexagesimal_divisions_of_calendar_time_and_day">Sexagesimal divisions of calendar time and day</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=9" title="Edit section: Sexagesimal divisions of calendar time and day"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Civilizations in the classic period and earlier created divisions of the calendar as well as arcs using a sexagesimal system of counting, so at that time the second was a sexagesimal subdivision of the day (ancient second<span class="nowrap"> </span>=<span class="nowrap"> </span><style data-mw-deduplicate="TemplateStyles:r1214402035">.mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="sfrac">⁠<span class="tion"><span class="num">day</span><span class="sr-only">/</span><span class="den">60×60</span></span>⁠</span>), not of the hour like the modern second (=<span class="nowrap"> </span><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num">hour</span><span class="sr-only">/</span><span class="den">60×60</span></span>⁠</span>). Sundials and water clocks were among the earliest timekeeping devices, and units of time were measured in degrees of arc. Conceptual units of time smaller than realisable on sundials were also used. </p><p>There are references to "second" as part of a lunar month in the writings of natural philosophers of the Middle Ages, which were mathematical subdivisions that could not be measured mechanically.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>nb 2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>nb 3<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Fraction_of_solar_day">Fraction of solar day</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=10" title="Edit section: Fraction of solar day"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The earliest mechanical clocks, which appeared starting in the 14th century, had displays that divided the hour into halves, thirds, quarters and sometimes even 12 parts, but never by 60. In fact, the hour was not commonly divided in 60 minutes as it was not uniform in duration. It was not practical for timekeepers to consider minutes until the first mechanical clocks that displayed minutes appeared near the end of the 16th century. Mechanical clocks kept the <i>mean time</i>, as opposed to the <i>apparent time</i> displayed by <a href="/wiki/Sundial" title="Sundial">sundials</a>. By that time, sexagesimal divisions of time were well established in Europe.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>nb 4<span class="cite-bracket">]</span></a></sup> </p><p>The earliest clocks to display seconds appeared during the last half of the 16th century. The second became accurately measurable with the development of mechanical clocks. The earliest spring-driven timepiece with a second hand that marked seconds is an unsigned clock depicting <a href="/wiki/Orpheus" title="Orpheus">Orpheus</a> in the Fremersdorf collection, dated between 1560 and <span class="nowrap">1570.<sup id="cite_ref-Landes_13-0" class="reference"><a href="#cite_note-Landes-13"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 417–418">: 417–418 </span></sup><sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup></span> During the 3rd quarter of the 16th century, <a href="/wiki/Taqi_al-Din_Muhammad_ibn_Ma%27ruf" class="mw-redirect" title="Taqi al-Din Muhammad ibn Ma'ruf">Taqi al-Din</a> built a clock with marks every 1/5 minute.<sup id="cite_ref-Selin1997_15-0" class="reference"><a href="#cite_note-Selin1997-15"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> In 1579, <a href="/wiki/Jost_B%C3%BCrgi" title="Jost Bürgi">Jost Bürgi</a> built a clock for <a href="/wiki/William_IV,_Landgrave_of_Hesse-Kassel" title="William IV, Landgrave of Hesse-Kassel">William of Hesse</a> that marked seconds.<sup id="cite_ref-Landes_13-1" class="reference"><a href="#cite_note-Landes-13"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 105">: 105 </span></sup> In 1581, <a href="/wiki/Tycho_Brahe" title="Tycho Brahe">Tycho Brahe</a> redesigned clocks that had displayed only minutes at his observatory so they also displayed seconds, even though those seconds were not accurate. In 1587, Tycho complained that his four clocks disagreed by plus or minus four seconds.<sup id="cite_ref-Landes_13-2" class="reference"><a href="#cite_note-Landes-13"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 104">: 104 </span></sup> </p><p>In 1656, Dutch scientist <a href="/wiki/Christiaan_Huygens" title="Christiaan Huygens">Christiaan Huygens</a> invented the first pendulum clock. It had a pendulum length of just under a meter, giving it a swing of one second, and an escapement that ticked every second. It was the first clock that could accurately keep time in seconds. By the 1730s, 80 years later, <a href="/wiki/John_Harrison" title="John Harrison">John Harrison</a>'s maritime chronometers could keep time accurate to within one second in 100 days. </p><p>In 1832, <a href="/wiki/Carl_Friedrich_Gauss" title="Carl Friedrich Gauss">Gauss</a> proposed using the second as the base unit of time in his millimeter–milligram–second <a href="/wiki/System_of_units" class="mw-redirect" title="System of units">system of units</a>. The <a href="/wiki/British_Association_for_the_Advancement_of_Science" class="mw-redirect" title="British Association for the Advancement of Science">British Association for the Advancement of Science</a> (BAAS) in 1862 stated that "All men of science are agreed to use the second of mean solar time as the unit of time."<sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> BAAS formally proposed the <a href="/wiki/CGS" class="mw-redirect" title="CGS">CGS system</a> in 1874, although this system was gradually replaced over the next 70 years by <a href="/wiki/MKS_system_of_units" class="mw-redirect" title="MKS system of units">MKS</a> units. Both the CGS and MKS systems used the same second as their base unit of time. MKS was adopted internationally during the 1940s, defining the second as <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">1</span>⁄<span class="den">86,400</span></span> of a mean solar day. </p> <div class="mw-heading mw-heading3"><h3 id="Fraction_of_an_ephemeris_year">Fraction of an ephemeris year</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=11" title="Edit section: Fraction of an ephemeris year"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Ephemeris_time" title="Ephemeris time">Ephemeris time</a></div> <p>Sometime in the late 1940s, quartz crystal oscillator clocks with an operating frequency of ~100 kHz advanced to keep time with accuracy better than 1 part in 10<sup>8</sup> over an operating period of a day. It became apparent that a consensus of such clocks kept better time than the rotation of the Earth. <a href="/wiki/Time_metrology" class="mw-redirect" title="Time metrology">Metrologists</a> also knew that Earth's orbit around the Sun (a year) was much more stable than Earth's rotation. This led to proposals as early as 1950 to define the second as a fraction of a year. </p><p>The Earth's motion was described in <a href="/wiki/Newcomb%27s_Tables_of_the_Sun" title="Newcomb's Tables of the Sun">Newcomb's <i>Tables of the Sun</i></a> (1895), which provided a formula for estimating the motion of the Sun relative to the epoch 1900 based on astronomical observations made between 1750 and 1892.<sup id="cite_ref-USNO_17-0" class="reference"><a href="#cite_note-USNO-17"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> This resulted in adoption of an <a href="/wiki/Ephemeris_time" title="Ephemeris time">ephemeris time</a> scale expressed in units of the <a href="/wiki/Sidereal_year" title="Sidereal year">sidereal year</a> at that epoch by the <a href="/wiki/International_Astronomical_Union" title="International Astronomical Union">IAU</a> in 1952.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> This extrapolated timescale brings the observed positions of the celestial bodies into accord with Newtonian dynamical theories of their motion.<sup id="cite_ref-USNO_17-1" class="reference"><a href="#cite_note-USNO-17"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> In 1955, the <a href="/wiki/Tropical_year" title="Tropical year">tropical year</a>, considered more fundamental than the sidereal year, was chosen by the IAU as the unit of time. The tropical year in the definition was not measured but calculated from a formula describing a mean tropical year that decreased linearly over time. </p><p>In 1956, the second was redefined in terms of a year relative to that <a href="/wiki/Epoch_(astronomy)" title="Epoch (astronomy)">epoch</a>. The second was thus defined as "the fraction <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">1</span>⁄<span class="den">31,556,925.9747</span></span> of the tropical year for 1900 <a href="/wiki/January_0" class="mw-redirect" title="January 0">January 0</a> at 12 hours ephemeris time".<sup id="cite_ref-USNO_17-2" class="reference"><a href="#cite_note-USNO-17"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> This definition was adopted as part of the <a href="/wiki/International_System_of_Units" title="International System of Units">International System of Units</a> in 1960.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Atomic_definition">Atomic definition</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=12" title="Edit section: Atomic definition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Even the best mechanical, electric motorized and quartz crystal-based clocks develop discrepancies from environmental conditions; far better for timekeeping is the natural and exact "vibration" in an energized atom. The frequency of vibration (i.e., radiation) is very specific depending on the type of atom and how it is excited.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> Since 1967, the second has been defined as exactly "the duration of 9,192,631,770 <a href="/wiki/Frequency" title="Frequency">periods</a> of the radiation corresponding to the transition between the two <a href="/wiki/Hyperfine_structure" title="Hyperfine structure">hyperfine levels</a> of the ground state of the <a href="/wiki/Caesium-133" class="mw-redirect" title="Caesium-133">caesium-133</a> atom". This length of a second was selected to correspond exactly to the length of the ephemeris second previously defined. Atomic clocks use such a frequency to measure seconds by counting cycles per second at that frequency. Radiation of this kind is one of the most stable and reproducible phenomena of nature. The current generation of atomic clocks is accurate to within one second in a few hundred million years. Since 1967, atomic clocks based on atoms other than caesium-133 have been developed with increased precision by a factor of 100. Therefore a new definition of the second is planned.<sup id="cite_ref-CGPM2022-Draft_21-0" class="reference"><a href="#cite_note-CGPM2022-Draft-21"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> </p><p>Atomic clocks now set the length of a second and the <a href="/wiki/Time_standard" title="Time standard">time standard</a> for the world.<sup id="cite_ref-McCarthy_2009_6-3" class="reference"><a href="#cite_note-McCarthy_2009-6"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 231–232">: 231–232 </span></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Table">Table</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=13" title="Edit section: Table"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table class="wikitable"> <tbody><tr> <th colspan="3">Evolution of the Second </th></tr> <tr> <th style="width: 40%;">Decisions of the CIPM </th> <th style="width: 40%;">Resolution of the CGPM </th> <th style="width: 20%;">Information </th></tr> <tr style="vertical-align: top;"> <td>That according to the decisions of the 8th General Assembly of the International Astronomical Union (Rome, 1952), the second of ephemeris time (ET) is the fraction <p><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {12960276813}{408986496}}\times 10^{-9}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mn>12960276813</mn> <mn>408986496</mn> </mfrac> </mrow> <mo>×</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>9</mn> </mrow> </msup> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {12960276813}{408986496}}\times 10^{-9}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/ad950199c04ea4aa913de31f3c79270649105b37" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.005ex; width:21.121ex; height:5.343ex;" alt="{\displaystyle {\frac {12960276813}{408986496}}\times 10^{-9}}"></span> of the tropical year for 1900 January 0 at 12 h ET. </p> </td> <td>The second is the fraction <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {1}{31556925.9747}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mn>1</mn> <mn>31556925.9747</mn> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {1}{31556925.9747}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/da0f004814709b55bfc1c3610a3bf0d3df48bd3c" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.005ex; width:15.432ex; height:5.343ex;" alt="{\displaystyle {\frac {1}{31556925.9747}}}"></span> of the tropical year for 1900 January 0 at 12 hours ephemeris time. </td> <td>1956 CIPM <p>11th CGPM 1960 Resolution 9 </p> </td></tr> <tr style="vertical-align: top;"> <td>The standard to be employed is the transition between the hyperfine levels F=4, M=0 and F=3, M=0 of the ground state <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle ^{2}S_{1/2}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msup> <mi></mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <msub> <mi>S</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>1</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mn>2</mn> </mrow> </msub> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle ^{2}S_{1/2}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/1bf4fd00ab156eb66679bf63661fef13980236f1" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.171ex; width:5.177ex; height:3.509ex;" alt="{\displaystyle ^{2}S_{1/2}}"></span> of the caesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9192631770 hertz. </td> <td>The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom </td> <td>13th CGPM Resolution 1 <p>CIPM 1967 </p> </td></tr> <tr style="vertical-align: top;"> <td>This definition implies that the caesium atom is at rest and unperturbed. In consequence, in its practical realization, measurements must be corrected for velocity of the atoms with respect to the clock reference frame, for magnetic and electric fields including ambient black-body radiation, for spin-exchange effects and for other possible perturbations. </td> <td>At its 1997 meeting, the CIPM affirmed that: This definition refers to a caesium atom at rest at a temperature of 0 K. This note was intended to make it clear that the definition of the SI second is based on a Cs atom unperturbed by black-body radiation, that is, in an environment whose temperature is 0 K, and that the frequencies of primary frequency standards should therefore be corrected for the shift due to ambient radiation, as stated at the meeting of the CCTF in 1999. </td> <td>footnote added by the 14th meeting of the Consultative Committee for Time and Frequency in 1999 <p>the footnote was added at the 86th (1997) meeting of the CIPM GCPM 1998 7th Edition SI Brochure </p> </td></tr> <tr style="vertical-align: top;"> <td>The definition of a unit refers to an idealized situation that can be reached in the practical realization with some uncertainty only. In this spirit, the definition of the second has to be understood as referring to atoms free of any perturbation, at rest and in the absence of electric and magnetic fields. <p>A future re-definition of the second would be justified if these idealized conditions can be achieved much easier than with the current definition. </p><p>The definition of the second should be understood as the definition of the unit of proper time: it applies in a small spatial domain that shares the motion of the caesium atom used to realize the definition. </p><p>In a laboratory sufficiently small to allow the effects of the non-uniformity of the gravitational field to be neglected when compared to the uncertainties of the realization of the second, the proper second is obtained after application of the special relativistic correction for the velocity of the atom in the laboratory. It is wrong to correct for the local gravitational field. </p> </td> <td><b>The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, Δ<i>ν</i><sub>Cs</sub>, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s<sup>−1</sup>.</b> <p>The reference to an unperturbed atom is intended to make it clear that the definition of the SI second is based on an isolated caesium atom that is unperturbed by any external field, such as ambient black-body radiation. </p><p>The second, so defined, is the unit of proper time in the sense of the general theory of relativity. To allow the provision of a coordinated time scale, the signals of different primary clocks in different locations are combined, which have to be corrected for relativistic caesium frequency shifts (see section 2.3.6). </p><p>The CIPM has adopted various secondary representations of the second, based on a selected number of spectral lines of atoms, ions or molecules. The unperturbed frequencies of these lines can be determined with a relative uncertainty not lower than that of the realization of the second based on the <sup>133</sup>Cs hyperfine transition frequency, but some can be reproduced with superior stability. </p> </td> <td><b>Current Definition</b> resolved in 2018 effective after the 26th GCPM approved the redefinition May 20, 2019. <p>SI Brochure 9 </p> </td></tr></tbody></table> <div class="mw-heading mw-heading2"><h2 id="Future_redefinition">Future redefinition</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=14" title="Edit section: Future redefinition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In 2022, the best realisation of the second is done with caesium primary standard clocks such as IT-CsF2, NIST-F2, NPL-CsF2, PTB-CSF2, SU–CsFO2 or SYRTE-FO2. These clocks work by laser-cooling a cloud of Cs atoms to a microkelvin in a magneto-optic trap. These cold atoms are then launched vertically by laser light. The atoms then undergo Ramsey excitation in a microwave cavity. The fraction of excited atoms is then detected by laser beams. These clocks have <span class="nowrap"><span data-sort-value="6984500000000000000♠"></span>5<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−16</sup></span> systematic uncertainty, which is equivalent to 50 picoseconds per day. A system of several fountains worldwide contribute to International Atomic Time. These caesium clocks also underpin optical frequency measurements. </p><p><a href="/wiki/Optical_clock" title="Optical clock">Optical clocks</a> are based on forbidden optical transitions in ions or atoms. They have frequencies around <span class="nowrap"><span data-sort-value="7015100000000000000♠"></span>10<sup>15</sup> Hz</span>, with a natural linewidth <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \Delta f}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi mathvariant="normal">Δ</mi> <mi>f</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \Delta f}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/ff38db24bc80b80a0a1ecfce75f3dca3fc79d54e" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:3.214ex; height:2.509ex;" alt="{\displaystyle \Delta f}"></span> of typically 1 Hz, so the <a href="/wiki/Q-factor" class="mw-redirect" title="Q-factor">Q-factor</a> is about <span class="nowrap"><span data-sort-value="7015100000000000000♠"></span>10<sup>15</sup></span>, or even higher. They have better stabilities than microwave clocks, which means that they can facilitate evaluation of lower uncertainties. They also have better time resolution, which means the clock "ticks" faster.<sup id="cite_ref-22" class="reference"><a href="#cite_note-22"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> Optical clocks use either a single ion, or an <a href="/wiki/Optical_lattice" title="Optical lattice">optical lattice</a> with <span class="nowrap"><span data-sort-value="7004100000000000000♠"></span>10<sup>4</sup></span>–<span class="nowrap"><span data-sort-value="7006100000000000000♠"></span>10<sup>6</sup></span> atoms. </p> <div class="mw-heading mw-heading3"><h3 id="Rydberg_constant">Rydberg constant</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=15" title="Edit section: Rydberg constant"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A definition based on the <a href="/wiki/Rydberg_constant" title="Rydberg constant">Rydberg constant</a> would involve fixing the value to a certain value: <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle R_{\infty }={\frac {m_{\text{e}}e^{4}}{8\varepsilon _{0}^{2}h^{3}c}}={\frac {m_{\text{e}}c\alpha ^{2}}{2h}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>R</mi> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">∞</mi> </mrow> </msub> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <msub> <mi>m</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>e</mtext> </mrow> </msub> <msup> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>4</mn> </mrow> </msup> </mrow> <mrow> <mn>8</mn> <msubsup> <mi>ε</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msubsup> <msup> <mi>h</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> </msup> <mi>c</mi> </mrow> </mfrac> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <msub> <mi>m</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>e</mtext> </mrow> </msub> <mi>c</mi> <msup> <mi>α</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mrow> <mrow> <mn>2</mn> <mi>h</mi> </mrow> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle R_{\infty }={\frac {m_{\text{e}}e^{4}}{8\varepsilon _{0}^{2}h^{3}c}}={\frac {m_{\text{e}}c\alpha ^{2}}{2h}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d6a7946d61e9d2ad3ef757eb09f3b9cffd33ab0c" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.005ex; width:24.76ex; height:6.843ex;" alt="{\displaystyle R_{\infty }={\frac {m_{\text{e}}e^{4}}{8\varepsilon _{0}^{2}h^{3}c}}={\frac {m_{\text{e}}c\alpha ^{2}}{2h}}}"></span>. The Rydberg constant describes the energy levels in a hydrogen atom with the nonrelativistic approximation <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle E_{n}\approx -{\frac {R_{\infty }ch}{n^{2}}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>E</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>n</mi> </mrow> </msub> <mo>≈</mo> <mo>−</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <msub> <mi>R</mi> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">∞</mi> </mrow> </msub> <mi>c</mi> <mi>h</mi> </mrow> <msup> <mi>n</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle E_{n}\approx -{\frac {R_{\infty }ch}{n^{2}}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d9649df314f8f21ef771f3f8a08b5f4866510844" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.171ex; width:14.662ex; height:5.676ex;" alt="{\displaystyle E_{n}\approx -{\frac {R_{\infty }ch}{n^{2}}}}"></span>. </p><p>The only viable way to fix the Rydberg constant involves trapping and cooling hydrogen. This is difficult because it is very light and the atoms move very fast, causing Doppler shifts. The radiation needed to cool the hydrogen – <span class="nowrap"><span data-sort-value="6993121500000000000♠"></span>121.5 nm</span> – is also difficult. Another hurdle involves improving the uncertainty in QED calculations, specifically the <a href="/wiki/Lamb_shift" title="Lamb shift">Lamb shift</a> in the 1s-2s transition of the hydrogen atom.<sup id="cite_ref-:10_23-0" class="reference"><a href="#cite_note-:10-23"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Requirements">Requirements</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=16" title="Edit section: Requirements"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A redefinition must include improved optical clock reliability. TAI must be contributed to by optical clocks before the BIPM affirms a redefinition. A consistent method of sending signals must be developed before the second is redefined, such as <a href="/wiki/Optical_fiber" title="Optical fiber">fiber-optics.</a><sup id="cite_ref-:10_23-1" class="reference"><a href="#cite_note-:10-23"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="SI_multiples">SI multiples</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=17" title="Edit section: SI multiples"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Orders_of_magnitude_(time)" title="Orders of magnitude (time)">Orders of magnitude (time)</a></div> <p><a href="/wiki/SI_prefix" class="mw-redirect" title="SI prefix">SI prefixes</a> are commonly used for times shorter than one second, but rarely for multiples of a second. Instead, certain <a href="/wiki/Non-SI_units_mentioned_in_the_SI" title="Non-SI units mentioned in the SI">non-SI units are permitted for use with SI</a>: <a href="/wiki/Minute" title="Minute">minutes</a>, <a href="/wiki/Hour" title="Hour">hours</a>, <a href="/wiki/Day" title="Day">days</a>, and in astronomy <a href="/wiki/Julian_year_(astronomy)" title="Julian year (astronomy)">Julian years</a>.<sup id="cite_ref-IAU_24-0" class="reference"><a href="#cite_note-IAU-24"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable"> <caption>SI multiples for second (s) </caption> <tbody><tr> <th colspan="3">Submultiples </th> <td rowspan="14"> </td> <th colspan="4">Multiples </th></tr> <tr> <th>Value </th> <th>SI symbol </th> <th>Name </th> <th>Value </th> <th>SI symbol </th> <th>Name </th> <th>Equivalent to </th></tr> <tr> <td>10<sup>−1</sup> s </td> <td>ds </td> <td>decisecond </td> <td>10<sup>1</sup> s </td> <td>das </td> <td>decasecond </td> <td>10 seconds </td></tr> <tr> <td>10<sup>−2</sup> s </td> <td>cs </td> <td>centisecond </td> <td>10<sup>2</sup> s </td> <td>hs </td> <td>hectosecond </td> <td>1 minute, 40 seconds </td></tr> <tr> <td>10<sup>−3</sup> s </td> <td>ms </td> <td><a href="/wiki/Millisecond" title="Millisecond">millisecond</a> </td> <td>10<sup>3</sup> s </td> <td>ks </td> <td>kilosecond </td> <td>16 minutes, 40 seconds </td></tr> <tr> <td>10<sup>−6</sup> s </td> <td>μs </td> <td><a href="/wiki/Microsecond" title="Microsecond">microsecond</a> </td> <td>10<sup>6</sup> s </td> <td>Ms </td> <td>megasecond </td> <td>11 days, 13 hours, 46 minutes, 40 seconds </td></tr> <tr> <td>10<sup>−9</sup> s </td> <td>ns </td> <td><a href="/wiki/Nanosecond" title="Nanosecond">nanosecond</a> </td> <td>10<sup>9</sup> s </td> <td>Gs </td> <td>gigasecond </td> <td>31.7 years </td></tr> <tr> <td>10<sup>−12</sup> s </td> <td>ps </td> <td><a href="/wiki/Picosecond" title="Picosecond">picosecond</a> </td> <td>10<sup>12</sup> s </td> <td>Ts </td> <td>terasecond </td> <td>31,700 years </td></tr> <tr> <td>10<sup>−15</sup> s </td> <td>fs </td> <td><a href="/wiki/Femtosecond" title="Femtosecond">femtosecond</a> </td> <td>10<sup>15</sup> s </td> <td>Ps </td> <td>petasecond </td> <td>31.7 million years </td></tr> <tr> <td>10<sup>−18</sup> s </td> <td>as </td> <td><a href="/wiki/Attosecond" title="Attosecond">attosecond</a> </td> <td>10<sup>18</sup> s </td> <td>Es </td> <td>exasecond </td> <td>31.7 billion years </td></tr> <tr> <td>10<sup>−21</sup> s </td> <td>zs </td> <td>zeptosecond </td> <td>10<sup>21</sup> s </td> <td>Zs </td> <td>zettasecond </td> <td>31.7 trillion years </td></tr> <tr> <td>10<sup>−24</sup> s </td> <td>ys </td> <td>yoctosecond </td> <td>10<sup>24</sup> s </td> <td>Ys </td> <td>yottasecond </td> <td>31.7 quadrillion years </td></tr> <tr> <td>10<sup>−27</sup> s </td> <td>rs </td> <td>rontosecond </td> <td>10<sup>27</sup> s </td> <td>Rs </td> <td>ronnasecond </td> <td>31.7 quintillion years </td></tr> <tr> <td>10<sup>−30</sup> s </td> <td>qs </td> <td>quectosecond </td> <td>10<sup>30</sup> s </td> <td>Qs </td> <td>quettasecond </td> <td>31.7 sextillion years </td></tr></tbody></table> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=18" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Caesium_standard" title="Caesium standard">Caesium standard</a></li> <li><a href="/wiki/Orders_of_magnitude_(time)" title="Orders of magnitude (time)">Orders of magnitude (time)</a></li> <li><a href="/wiki/Seconds_pendulum" title="Seconds pendulum">Seconds pendulum</a></li> <li><a href="/wiki/Time_standard" title="Time standard">Time standard</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="Notes">Notes</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=19" title="Edit section: Notes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><a href="/wiki/Civil_time" title="Civil time">Civil time</a> is set, directly or indirectly, to <a href="/wiki/Coordinated_Universal_Time" title="Coordinated Universal Time">Coordinated Universal Time</a>, which includes leap seconds. Other time scales are used in scientific and technical fields that do not contain leap seconds.</span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text">In 1000, the <a href="/wiki/Persian_people" class="mw-redirect" title="Persian people">Persian</a> scholar <a href="/wiki/Al-Biruni" title="Al-Biruni">al-Biruni</a>, writing in Arabic, used the term <i>second</i>, and defined the division of time between <a href="/wiki/New_moon" title="New moon">new moons</a> of certain specific weeks as a number of days, hours, minutes, seconds, thirds, and fourths after noon Sunday.<sup id="cite_ref-al-Biruni_8-0" class="reference"><a href="#cite_note-al-Biruni-8"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup></span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text">In 1267, the medieval English scientist <a href="/wiki/Roger_Bacon" title="Roger Bacon">Roger Bacon</a>, writing in Latin, defined the division of time between <a href="/wiki/Full_moon" title="Full moon">full moons</a> as a number of hours, minutes, seconds, thirds, and fourths (<i>horae</i>, <i>minuta</i>, <i>secunda</i>, <i>tertia</i>, and <i>quarta</i>) after noon on specified calendar dates.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup></span> </li> <li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text">It may be noted that 60 is the smallest multiple of the first 6 counting numbers. So a clock with 60 divisions would have a mark for thirds, fourths, fifths, sixths and twelfths (the hours); whatever units the clock would likely keep time in, would have marks.</span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=20" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239543626"><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-BIPM9-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-BIPM9_1-0">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9.pdf">"SI Brochure (2019)"</a> <span class="cs1-format">(PDF)</span>. <i>SI Brochure</i>. <a href="/wiki/BIPM" class="mw-redirect" title="BIPM">BIPM</a>. p. 130. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190523222919/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9.pdf">Archived</a> <span class="cs1-format">(PDF)</span> from the original on May 23, 2019<span class="reference-accessdate">. Retrieved <span class="nowrap">May 23,</span> 2019</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=SI+Brochure&rft.atitle=SI+Brochure+%282019%29&rft.pages=130&rft_id=https%3A%2F%2Fwww.bipm.org%2Futils%2Fcommon%2Fpdf%2Fsi-brochure%2FSI-Brochure-9.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGill2011" class="citation journal cs1">Gill, Patrick (October 28, 2011). <a rel="nofollow" class="external text" href="https://doi.org/10.1098%2Frsta.2011.0237">"When should we change the definition of the second?"</a>. <i>Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences</i>. <b>369</b> (1953): 4109–4130. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2011RSPTA.369.4109G">2011RSPTA.369.4109G</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1098%2Frsta.2011.0237">10.1098/rsta.2011.0237</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/21930568">21930568</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:6896025">6896025</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Philosophical+Transactions+of+the+Royal+Society+A%3A+Mathematical%2C+Physical+and+Engineering+Sciences&rft.atitle=When+should+we+change+the+definition+of+the+second%3F&rft.volume=369&rft.issue=1953&rft.pages=4109-4130&rft.date=2011-10-28&rft_id=info%3Adoi%2F10.1098%2Frsta.2011.0237&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A6896025%23id-name%3DS2CID&rft_id=info%3Apmid%2F21930568&rft_id=info%3Abibcode%2F2011RSPTA.369.4109G&rft.aulast=Gill&rft.aufirst=Patrick&rft_id=https%3A%2F%2Fdoi.org%2F10.1098%252Frsta.2011.0237&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.etymonline.com/word/second#etymonline_v_23075">"second | Etymology of second by etymonline"</a>. <i>www.etymonline.com</i><span class="reference-accessdate">. Retrieved <span class="nowrap">October 4,</span> 2024</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.etymonline.com&rft.atitle=second+%7C+Etymology+of+second+by+etymonline&rft_id=https%3A%2F%2Fwww.etymonline.com%2Fword%2Fsecond%23etymonline_v_23075&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.britannica.com/science/mathematics">"mathematics – Ancient mathematical sources"</a>. <i>Encyclopedia Britannica</i><span class="reference-accessdate">. Retrieved <span class="nowrap">September 20,</span> 2021</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Encyclopedia+Britannica&rft.atitle=mathematics+%E2%80%93+Ancient+mathematical+sources&rft_id=https%3A%2F%2Fwww.britannica.com%2Fscience%2Fmathematics&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-McCarthy_2009-6"><span class="mw-cite-backlink">^ <a href="#cite_ref-McCarthy_2009_6-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-McCarthy_2009_6-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-McCarthy_2009_6-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-McCarthy_2009_6-3"><sup><i><b>d</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMcCarthySeidelmann2009" class="citation book cs1"><a href="/wiki/Dennis_McCarthy_(scientist)" title="Dennis McCarthy (scientist)">McCarthy, Dennis D.</a>; Seidelmann, P. Kenneth (2009). <i>Time: From Earth Rotation to Atomic Physics</i>. Weinheim: Wiley.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Time%3A+From+Earth+Rotation+to+Atomic+Physics&rft.place=Weinheim&rft.pub=Wiley&rft.date=2009&rft.aulast=McCarthy&rft.aufirst=Dennis+D.&rft.au=Seidelmann%2C+P.+Kenneth&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFVincent2015" class="citation web cs1">Vincent, James (April 22, 2015). <a rel="nofollow" class="external text" href="https://www.theverge.com/2015/4/22/8466681/most-accurate-atomic-clock-optical-lattice-strontium">"The most accurate clock ever built only loses one second every 15 billion years"</a>. <i>TheVerge</i>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20180127084115/https://www.theverge.com/2015/4/22/8466681/most-accurate-atomic-clock-optical-lattice-strontium">Archived</a> from the original on January 27, 2018<span class="reference-accessdate">. Retrieved <span class="nowrap">January 26,</span> 2018</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=TheVerge&rft.atitle=The+most+accurate+clock+ever+built+only+loses+one+second+every+15+billion+years&rft.date=2015-04-22&rft.aulast=Vincent&rft.aufirst=James&rft_id=https%3A%2F%2Fwww.theverge.com%2F2015%2F4%2F22%2F8466681%2Fmost-accurate-atomic-clock-optical-lattice-strontium&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-al-Biruni-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-al-Biruni_8-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAl-Biruni1879" class="citation book cs1"><a href="/wiki/Al-Biruni" title="Al-Biruni">Al-Biruni</a> (1879) [1000]. <a rel="nofollow" class="external text" href="https://books.google.com/books?id=pFIEAAAAIAAJ&pg=PA148"><i>The chronology of ancient nations</i></a>. Translated by Sachau, C. Edward. pp. 147–149. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190916000857/https://books.google.com/books?id=pFIEAAAAIAAJ&pg=PA148&hl=en#v=onepage&q=">Archived</a> from the original on September 16, 2019<span class="reference-accessdate">. Retrieved <span class="nowrap">February 23,</span> 2016</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+chronology+of+ancient+nations&rft.pages=147-149&rft.date=1879&rft.au=Al-Biruni&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DpFIEAAAAIAAJ%26pg%3DPA148&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBacon2000" class="citation book cs1">Bacon, Roger (2000) [1267]. <i>The Opus Majus of Roger Bacon</i>. translated by Robert Belle Burke. <a href="/wiki/University_of_Pennsylvania_Press" title="University of Pennsylvania Press">University of Pennsylvania Press</a>. table facing page 231. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/1-85506-856-7" title="Special:BookSources/1-85506-856-7"><bdi>1-85506-856-7</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Opus+Majus+of+Roger+Bacon&rft.pages=table+facing+page+231&rft.pub=University+of+Pennsylvania+Press&rft.date=2000&rft.isbn=1-85506-856-7&rft.aulast=Bacon&rft.aufirst=Roger&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-Landes-13"><span class="mw-cite-backlink">^ <a href="#cite_ref-Landes_13-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Landes_13-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Landes_13-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLandes1983" class="citation book cs1"><a href="/wiki/David_S._Landes" class="mw-redirect" title="David S. Landes">Landes, David S.</a> (1983). <i><a href="/wiki/Revolution_in_Time" title="Revolution in Time">Revolution in Time</a></i>. Cambridge, Massachusetts: Harvard University Press. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-674-76802-7" title="Special:BookSources/0-674-76802-7"><bdi>0-674-76802-7</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Revolution+in+Time&rft.place=Cambridge%2C+Massachusetts&rft.pub=Harvard+University+Press&rft.date=1983&rft.isbn=0-674-76802-7&rft.aulast=Landes&rft.aufirst=David+S.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFWillsberger1975" class="citation book cs1">Willsberger, Johann (1975). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/clockswatchessix0000will"><i>Clocks & watches</i></a></span>. New York: Dial Press. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-8037-4475-7" title="Special:BookSources/0-8037-4475-7"><bdi>0-8037-4475-7</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Clocks+%26+watches&rft.place=New+York&rft.pub=Dial+Press&rft.date=1975&rft.isbn=0-8037-4475-7&rft.aulast=Willsberger&rft.aufirst=Johann&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fclockswatchessix0000will&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span> full page color photo: 4th caption page, 3rd photo thereafter (neither pages nor photos are numbered).</span> </li> <li id="cite_note-Selin1997-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-Selin1997_15-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSelin1997" class="citation book cs1"><a href="/wiki/Helaine_Selin" title="Helaine Selin">Selin, Helaine</a> (July 31, 1997). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=raKRY3KQspsC&pg=PA934"><i>Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures</i></a>. Springer Science & Business Media. p. 934. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-7923-4066-3" title="Special:BookSources/0-7923-4066-3"><bdi>0-7923-4066-3</bdi></a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20161120013247/https://books.google.com/books?id=raKRY3KQspsC&pg=PA934">Archived</a> from the original on November 20, 2016<span class="reference-accessdate">. Retrieved <span class="nowrap">February 23,</span> 2016</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Encyclopaedia+of+the+History+of+Science%2C+Technology%2C+and+Medicine+in+Non-Western+Cultures&rft.pages=934&rft.pub=Springer+Science+%26+Business+Media&rft.date=1997-07-31&rft.isbn=0-7923-4066-3&rft.aulast=Selin&rft.aufirst=Helaine&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DraKRY3KQspsC%26pg%3DPA934&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-16">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFJenkin1873" class="citation book cs1"><a href="/wiki/Henry_Charles_Fleeming_Jenkin" class="mw-redirect" title="Henry Charles Fleeming Jenkin">Jenkin, Henry Charles Fleeming</a>, ed. (1873). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=540DAAAAQAAJ&pg=PR1"><i>Reports of the committee on electrical standards</i></a>. British Association for the Advancement of Science. p. 90. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20161120015337/https://books.google.com/books?id=540DAAAAQAAJ&pg=PR1#v=onepage&q&f=true">Archived</a> from the original on November 20, 2016<span class="reference-accessdate">. Retrieved <span class="nowrap">February 23,</span> 2016</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Reports+of+the+committee+on+electrical+standards&rft.pages=90&rft.pub=British+Association+for+the+Advancement+of+Science&rft.date=1873&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D540DAAAAQAAJ%26pg%3DPR1&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-USNO-17"><span class="mw-cite-backlink">^ <a href="#cite_ref-USNO_17-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-USNO_17-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-USNO_17-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://tycho.usno.navy.mil/leapsec.html">"Leap Seconds"</a>. Time Service Department, <a href="/wiki/United_States_Naval_Observatory" title="United States Naval Observatory">United States Naval Observatory</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150312003149/http://tycho.usno.navy.mil/leapsec.html">Archived</a> from the original on March 12, 2015<span class="reference-accessdate">. Retrieved <span class="nowrap">November 22,</span> 2015</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Leap+Seconds&rft.pub=Time+Service+Department%2C+United+States+Naval+Observatory&rft_id=http%3A%2F%2Ftycho.usno.navy.mil%2Fleapsec.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-18">^</a></b></span> <span class="reference-text"> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFNautical_Almanac_Offices_of_the_United_Kingdom_and_the_United_States_of_America1961" class="citation cs2">Nautical Almanac Offices of the United Kingdom and the United States of America (1961), <a rel="nofollow" class="external text" href="https://archive.org/details/explanatorysupplement/page/n19"><i>Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac</i></a>, p. 9, <q>... defined ephemeris time ... [was] adopted by the <a href="/wiki/International_Astronomical_Union" title="International Astronomical Union">International Astronomical Union</a> in Sept. 1952.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Explanatory+Supplement+to+the+Astronomical+Ephemeris+and+the+American+Ephemeris+and+Nautical+Almanac&rft.pages=9&rft.date=1961&rft.au=Nautical+Almanac+Offices+of+the+United+Kingdom+and+the+United+States+of+America&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fexplanatorysupplement%2Fpage%2Fn19&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-19">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.bipm.org/utils/common/pdf/si_brochure_8.pdf">"SI Brochure (2006)"</a> <span class="cs1-format">(PDF)</span>. <i>SI Brochure 8th Edition</i>. <a href="/wiki/BIPM" class="mw-redirect" title="BIPM">BIPM</a>. p. 112. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190503133741/https://www1.bipm.org/utils/common/pdf/si_brochure_8.pdf">Archived</a> <span class="cs1-format">(PDF)</span> from the original on May 3, 2019<span class="reference-accessdate">. Retrieved <span class="nowrap">May 23,</span> 2019</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=SI+Brochure+8th+Edition&rft.atitle=SI+Brochure+%282006%29&rft.pages=112&rft_id=https%3A%2F%2Fwww.bipm.org%2Futils%2Fcommon%2Fpdf%2Fsi_brochure_8.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-20">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMcCarthySeidelmann2009" class="citation book cs1"><a href="/wiki/Dennis_McCarthy_(scientist)" title="Dennis McCarthy (scientist)">McCarthy, Dennis D.</a>; Seidelmann, P. Kenneth (2009). "Definition and Role of a Second". <i>Time: From Earth Rotation to Atomic Physics</i>. Weinheim: Wiley.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Definition+and+Role+of+a+Second&rft.btitle=Time%3A+From+Earth+Rotation+to+Atomic+Physics&rft.place=Weinheim&rft.pub=Wiley&rft.date=2009&rft.aulast=McCarthy&rft.aufirst=Dennis+D.&rft.au=Seidelmann%2C+P.+Kenneth&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-CGPM2022-Draft-21"><span class="mw-cite-backlink"><b><a href="#cite_ref-CGPM2022-Draft_21-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://www.bipm.org/documents/20126/64811571/Draft-Resolutions-2022.pdf/2e8e53df-7a14-3fc8-8a04-42dd47df1a04?t=1644502962693">Draft resolutions</a> of the 27. <a href="/wiki/General_Conference_on_Weights_and_Measures" title="General Conference on Weights and Measures">General Conference on Weights and Measures</a> in November 2022, Section E, p. 25</span> </li> <li id="cite_note-22"><span class="mw-cite-backlink"><b><a href="#cite_ref-22">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFNational_Physical_Laboratory2011" class="citation journal cs1">National Physical Laboratory (2011). "When should we change the definition of the second?". <i>Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences</i>. <b>369</b> (1953): 4109–4130. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2011RSPTA.369.4109G">2011RSPTA.369.4109G</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1098%2Frsta.2011.0237">10.1098/rsta.2011.0237</a>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/21930568">21930568</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:6896025">6896025</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Philosophical+Transactions+of+the+Royal+Society+A%3A+Mathematical%2C+Physical+and+Engineering+Sciences&rft.atitle=When+should+we+change+the+definition+of+the+second%3F&rft.volume=369&rft.issue=1953&rft.pages=4109-4130&rft.date=2011&rft_id=info%3Adoi%2F10.1098%2Frsta.2011.0237&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A6896025%23id-name%3DS2CID&rft_id=info%3Apmid%2F21930568&rft_id=info%3Abibcode%2F2011RSPTA.369.4109G&rft.au=National+Physical+Laboratory&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-:10-23"><span class="mw-cite-backlink">^ <a href="#cite_ref-:10_23-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:10_23-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGill2011" class="citation journal cs1">Gill, Patrick (October 28, 2011). <a rel="nofollow" class="external text" href="https://doi.org/10.1098%2Frsta.2011.0237">"When should we change the definition of the second?"</a>. <i>Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences</i>. <b>369</b> (1953): 4109–4130. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2011RSPTA.369.4109G">2011RSPTA.369.4109G</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1098%2Frsta.2011.0237">10.1098/rsta.2011.0237</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/21930568">21930568</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:6896025">6896025</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Philosophical+Transactions+of+the+Royal+Society+A%3A+Mathematical%2C+Physical+and+Engineering+Sciences&rft.atitle=When+should+we+change+the+definition+of+the+second%3F&rft.volume=369&rft.issue=1953&rft.pages=4109-4130&rft.date=2011-10-28&rft_id=info%3Adoi%2F10.1098%2Frsta.2011.0237&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A6896025%23id-name%3DS2CID&rft_id=info%3Apmid%2F21930568&rft_id=info%3Abibcode%2F2011RSPTA.369.4109G&rft.aulast=Gill&rft.aufirst=Patrick&rft_id=https%3A%2F%2Fdoi.org%2F10.1098%252Frsta.2011.0237&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span></span> </li> <li id="cite_note-IAU-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-IAU_24-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFInternational_Astronomical_Union" class="citation web cs1">International Astronomical Union. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20070216041250/http://www.iau.org/Units.234.0.html">"Recommendations Concerning Units"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.iau.org/Units.234.0.html">the original</a> on February 16, 2007<span class="reference-accessdate">. Retrieved <span class="nowrap">February 18,</span> 2007</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Recommendations+Concerning+Units&rft.au=International+Astronomical+Union&rft_id=http%3A%2F%2Fwww.iau.org%2FUnits.234.0.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASecond" class="Z3988"></span> Reprinted from the "IAU Style Manual" by G.A. Wilkinson, Comm. 5, in IAU Transactions XXB (1987).</span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Second&action=edit&section=21" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1235681985">.mw-parser-output .side-box{margin:4px 0;box-sizing:border-box;border:1px solid #aaa;font-size:88%;line-height:1.25em;background-color:var(--background-color-interactive-subtle,#f8f9fa);display:flow-root}.mw-parser-output .side-box-abovebelow,.mw-parser-output .side-box-text{padding:0.25em 0.9em}.mw-parser-output .side-box-image{padding:2px 0 2px 0.9em;text-align:center}.mw-parser-output .side-box-imageright{padding:2px 0.9em 2px 0;text-align:center}@media(min-width:500px){.mw-parser-output .side-box-flex{display:flex;align-items:center}.mw-parser-output .side-box-text{flex:1;min-width:0}}@media(min-width:720px){.mw-parser-output .side-box{width:238px}.mw-parser-output .side-box-right{clear:right;float:right;margin-left:1em}.mw-parser-output .side-box-left{margin-right:1em}}</style><style data-mw-deduplicate="TemplateStyles:r1237033735">@media print{body.ns-0 .mw-parser-output .sistersitebox{display:none!important}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}</style><div class="side-box side-box-right plainlinks sistersitebox"><style data-mw-deduplicate="TemplateStyles:r1126788409">.mw-parser-output .plainlist ol,.mw-parser-output .plainlist ul{line-height:inherit;list-style:none;margin:0;padding:0}.mw-parser-output .plainlist ol li,.mw-parser-output .plainlist ul li{margin-bottom:0}</style> <div class="side-box-flex"> <div class="side-box-image"><span class="noviewer" typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/40px-Wiktionary-logo-en-v2.svg.png" decoding="async" width="40" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/60px-Wiktionary-logo-en-v2.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/80px-Wiktionary-logo-en-v2.svg.png 2x" data-file-width="512" data-file-height="512" /></span></span></div> <div class="side-box-text plainlist">Look up <i><b><a href="https://en.wiktionary.org/wiki/second" class="extiw" title="wiktionary:second">second</a></b></i> in Wiktionary, the free dictionary.</div></div> </div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1235681985"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1237033735"><div class="side-box side-box-right plainlinks sistersitebox"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"> <div class="side-box-flex"> <div class="side-box-image"><span class="noviewer" typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png" decoding="async" width="30" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/45px-Commons-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/59px-Commons-logo.svg.png 2x" data-file-width="1024" data-file-height="1376" /></span></span></div> <div class="side-box-text plainlist">Wikimedia Commons has media related to <a href="https://commons.wikimedia.org/wiki/Second" class="extiw" title="commons:Second"><span style="font-style:italic; font-weight:bold;">Second</span></a>.</div></div> </div> <ul><li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20160407215419/http://www.npl.co.uk/science-technology/time-frequency/research/optical-frequency-standards/trapped-ion-optical-frequency-standards">National Physical Laboratory: <i>Trapped ion optical frequency standards</i> </a></li> <li><a rel="nofollow" class="external text" href="http://resource.npl.co.uk/docs/networks/time/meeting3/klein.pdf"><i>High-accuracy strontium ion optical clock</i>; National Physical Laboratory (2005)</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20080314011450/http://inms-ienm.nrc-cnrc.gc.ca/research/optical_frequency_projects_e.html#optical">National Research Council of Canada: <i>Optical frequency standard based on a single trapped ion</i></a></li> <li><a rel="nofollow" class="external text" href="http://physics.nist.gov/cuu/Units/second.html">NIST: <i>Definition of the second</i>; notice the cesium atom must be in its ground state at 0 K</a></li> <li><a rel="nofollow" class="external text" href="http://www.bipm.org/en/publications/si-brochure/second.html">Official BIPM definition of the second</a></li> <li><a rel="nofollow" class="external text" href="http://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The leap second: its history and possible future</a></li> <li><a rel="nofollow" class="external text" href="http://www.nrc-cnrc.gc.ca/eng/services/time/faq/index.html#Q10"><i>What is a Cesium atom clock?</i></a></li> <li><a rel="nofollow" class="external text" href="https://home.slac.stanford.edu/scales-of-time/index.html">SLAC: Scales of Time – Our universe from 10<sup>18</sup> to 10<sup>−18</sup> seconds</a></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}</style><style data-mw-deduplicate="TemplateStyles:r1236075235">.mw-parser-output .navbox{box-sizing:border-box;border:1px solid #a2a9b1;width:100%;clear:both;font-size:88%;text-align:center;padding:1px;margin:1em auto 0}.mw-parser-output .navbox .navbox{margin-top:0}.mw-parser-output .navbox+.navbox,.mw-parser-output .navbox+.navbox-styles+.navbox{margin-top:-1px}.mw-parser-output .navbox-inner,.mw-parser-output .navbox-subgroup{width:100%}.mw-parser-output .navbox-group,.mw-parser-output .navbox-title,.mw-parser-output .navbox-abovebelow{padding:0.25em 1em;line-height:1.5em;text-align:center}.mw-parser-output .navbox-group{white-space:nowrap;text-align:right}.mw-parser-output .navbox,.mw-parser-output .navbox-subgroup{background-color:#fdfdfd}.mw-parser-output .navbox-list{line-height:1.5em;border-color:#fdfdfd}.mw-parser-output .navbox-list-with-group{text-align:left;border-left-width:2px;border-left-style:solid}.mw-parser-output tr+tr>.navbox-abovebelow,.mw-parser-output tr+tr>.navbox-group,.mw-parser-output tr+tr>.navbox-image,.mw-parser-output tr+tr>.navbox-list{border-top:2px solid #fdfdfd}.mw-parser-output .navbox-title{background-color:#ccf}.mw-parser-output .navbox-abovebelow,.mw-parser-output .navbox-group,.mw-parser-output .navbox-subgroup .navbox-title{background-color:#ddf}.mw-parser-output .navbox-subgroup .navbox-group,.mw-parser-output .navbox-subgroup .navbox-abovebelow{background-color:#e6e6ff}.mw-parser-output .navbox-even{background-color:#f7f7f7}.mw-parser-output .navbox-odd{background-color:transparent}.mw-parser-output .navbox .hlist td dl,.mw-parser-output .navbox .hlist td ol,.mw-parser-output .navbox .hlist td ul,.mw-parser-output .navbox td.hlist dl,.mw-parser-output .navbox td.hlist ol,.mw-parser-output .navbox td.hlist ul{padding:0.125em 0}.mw-parser-output .navbox .navbar{display:block;font-size:100%}.mw-parser-output .navbox-title .navbar{float:left;text-align:left;margin-right:0.5em}body.skin--responsive .mw-parser-output .navbox-image img{max-width:none!important}@media print{body.ns-0 .mw-parser-output .navbox{display:none!important}}</style><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"></div><div role="navigation" class="navbox" aria-labelledby="Time" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Time_topics" title="Template:Time topics"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Time_topics" title="Template talk:Time topics"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Time_topics" title="Special:EditPage/Template:Time topics"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Time" style="font-size:114%;margin:0 4em"><a href="/wiki/Time" title="Time">Time</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Key concepts</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Past" title="Past">Past</a></li> <li><a href="/wiki/Present" title="Present">Present</a></li> <li><a href="/wiki/Future" title="Future">Future</a></li> <li><a href="/wiki/Eternity" title="Eternity">Eternity</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Horology" class="mw-redirect" title="Horology">Measurement</a><br />and <a href="/wiki/Time_standard" title="Time standard">standards</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:6.5em;font-weight:normal; text-align:center;"><a href="/wiki/Chronometry" title="Chronometry">Chronometry</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Coordinated_Universal_Time" title="Coordinated Universal Time">UTC</a></li> <li><a href="/wiki/Universal_Time" title="Universal Time">UT</a></li> <li><a href="/wiki/International_Atomic_Time" title="International Atomic Time">TAI</a></li> <li><a href="/wiki/Unit_of_time" title="Unit of time">Unit of time</a></li> <li><a href="/wiki/Orders_of_magnitude_(time)" title="Orders of magnitude (time)">Orders of magnitude (time)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:6.5em;font-weight:normal; text-align:center;"><a href="/wiki/System_of_measurement" class="mw-redirect" title="System of measurement">Measurement<br />systems</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Italian_six-hour_clock" title="Italian six-hour clock">Italian six-hour clock</a></li> <li><a href="/wiki/Thai_six-hour_clock" title="Thai six-hour clock">Thai six-hour clock</a></li> <li><a href="/wiki/12-hour_clock" title="12-hour clock">12-hour clock</a></li> <li><a href="/wiki/24-hour_clock" title="24-hour clock">24-hour clock</a></li> <li><a href="/wiki/Relative_hour" title="Relative hour">Relative hour</a></li> <li><a href="/wiki/Daylight_saving_time" title="Daylight saving time">Daylight saving time</a></li> <li><a href="/wiki/Traditional_Chinese_timekeeping" title="Traditional Chinese timekeeping">Chinese</a></li> <li><a href="/wiki/Decimal_time" title="Decimal time">Decimal</a></li> <li><a href="/wiki/Hexadecimal_time" title="Hexadecimal time">Hexadecimal</a></li> <li><a href="/wiki/Hindu_units_of_time" title="Hindu units of time">Hindu</a></li> <li><a href="/wiki/Metric_time" title="Metric time">Metric</a></li> <li><a href="/wiki/Roman_timekeeping" title="Roman timekeeping">Roman</a></li> <li><a href="/wiki/Sidereal_time" title="Sidereal time">Sidereal</a></li> <li><a href="/wiki/Solar_time" title="Solar time">Solar</a></li> <li><a href="/wiki/Time_zone" title="Time zone">Time zone</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:6.5em;font-weight:normal; text-align:center;"><a href="/wiki/Calendar" title="Calendar">Calendars</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Calendar#Systems" title="Calendar">Main types</a> <ul><li><a href="/wiki/Solar_calendar" title="Solar calendar">Solar</a></li> <li><a href="/wiki/Lunar_calendar" title="Lunar calendar">Lunar</a></li> <li><a href="/wiki/Lunisolar_calendar" title="Lunisolar calendar">Lunisolar</a></li></ul></li> <li><a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian</a></li> <li><a href="/wiki/Julian_calendar" title="Julian calendar">Julian</a></li> <li><a href="/wiki/Hebrew_calendar" title="Hebrew calendar">Hebrew</a></li> <li><a href="/wiki/Islamic_calendar" title="Islamic calendar">Islamic</a></li> <li><a href="/wiki/Solar_Hijri_calendar" title="Solar Hijri calendar">Solar Hijri</a></li> <li><a href="/wiki/Chinese_calendar" title="Chinese calendar">Chinese</a></li> <li><a href="/wiki/Hindu_calendar" title="Hindu calendar">Hindu Panchang</a></li> <li><a href="/wiki/Maya_calendar" title="Maya calendar">Maya</a></li> <li><i><a href="/wiki/List_of_calendars" title="List of calendars">List</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:6.5em;font-weight:normal; text-align:center;"><a href="/wiki/Clock" title="Clock">Clocks</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Clock#Types" title="Clock">Main types</a> <ul><li><a href="/wiki/Astronomical_clock" title="Astronomical clock">astronomical</a> <ul><li><a href="/wiki/Astrarium" title="Astrarium">astrarium</a></li></ul></li> <li><a href="/wiki/Atomic_clock" title="Atomic clock">atomic</a> <ul><li><a href="/wiki/Quantum_clock" class="mw-redirect" title="Quantum clock">quantum</a></li></ul></li> <li><a href="/wiki/Hourglass" title="Hourglass">hourglass</a></li> <li><a href="/wiki/Marine_chronometer" title="Marine chronometer">marine</a></li> <li><a href="/wiki/Sundial" title="Sundial">sundial</a></li> <li><a href="/wiki/Watch" title="Watch">watch</a> <ul><li><a href="/wiki/Mechanical_watch" title="Mechanical watch">mechanical</a></li> <li><a href="/wiki/Stopwatch" title="Stopwatch">stopwatch</a></li></ul></li> <li><a href="/wiki/Water_clock" title="Water clock">water-based</a></li></ul></li> <li><a href="/wiki/Cuckoo_clock" title="Cuckoo clock">Cuckoo clock</a></li> <li><a href="/wiki/Digital_clock" title="Digital clock">Digital clock</a></li> <li><a href="/wiki/Grandfather_clock" title="Grandfather clock">Grandfather clock</a></li> <li><i><a href="/wiki/History_of_timekeeping_devices" title="History of timekeeping devices">History</a></i> <ul><li><i><a href="/wiki/Timeline_of_time_measurement_inventions" title="Timeline of time measurement inventions">Timeline</a></i></li></ul></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div class="hlist"><ul><li><a href="/wiki/Chronology" title="Chronology">Chronology</a></li><li><a href="/wiki/History" title="History">History</a></li></ul></div></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Astronomical_chronology" title="Astronomical chronology">Astronomical chronology</a></li> <li><a href="/wiki/Big_History" title="Big History">Big History</a></li> <li><a href="/wiki/Calendar_era" title="Calendar era">Calendar era</a></li> <li><a href="/wiki/Deep_time" title="Deep time">Deep time</a></li> <li><a href="/wiki/Periodization" title="Periodization">Periodization</a></li> <li><a href="/wiki/Regnal_year" title="Regnal year">Regnal year</a></li> <li><a href="/wiki/Timeline" title="Timeline">Timeline</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Philosophy_of_space_and_time" title="Philosophy of space and time">Philosophy of time</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/A_series_and_B_series" title="A series and B series">A series and B series</a></li> <li><a href="/wiki/B-theory_of_time" title="B-theory of time">B-theory of time</a></li> <li><a href="/wiki/Chronocentrism" title="Chronocentrism">Chronocentrism</a></li> <li><a href="/wiki/Duration_(philosophy)" title="Duration (philosophy)">Duration</a></li> <li><a href="/wiki/Endurantism" title="Endurantism">Endurantism</a></li> <li><a href="/wiki/Eternal_return" title="Eternal return">Eternal return</a></li> <li><a href="/wiki/Eternalism_(philosophy_of_time)" title="Eternalism (philosophy of time)">Eternalism</a></li> <li><a href="/wiki/Event_(philosophy)" title="Event (philosophy)">Event</a></li> <li><a href="/wiki/Perdurantism" title="Perdurantism">Perdurantism</a></li> <li><a href="/wiki/Philosophical_presentism" title="Philosophical presentism">Presentism</a></li> <li><a href="/wiki/Temporal_finitism" title="Temporal finitism">Temporal finitism</a></li> <li><a href="/wiki/Temporal_parts" title="Temporal parts">Temporal parts</a></li> <li><i><a href="/wiki/The_Unreality_of_Time" title="The Unreality of Time">The Unreality of Time</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div class="hlist"><ul><li><a href="/wiki/Category:Time_in_religion" title="Category:Time in religion">Religion</a></li><li><a href="/wiki/Template:Time_in_religion_and_mythology" title="Template:Time in religion and mythology">Mythology</a></li></ul></div></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ages_of_Man" title="Ages of Man">Ages of Man</a></li> <li><a href="/wiki/Destiny" title="Destiny">Destiny</a></li> <li><a href="/wiki/Immortality" title="Immortality">Immortality</a></li> <li><a href="/wiki/The_Dreaming" title="The Dreaming">Dreamtime</a></li> <li><a href="/wiki/K%C4%81la" title="Kāla">Kāla</a></li> <li><a href="/wiki/Time_and_fate_deities" title="Time and fate deities">Time and fate deities</a> <ul><li><a href="/wiki/Father_Time" title="Father Time">Father Time</a></li></ul></li> <li><a href="/wiki/Wheel_of_time" title="Wheel of time">Wheel of time</a> <ul><li><a href="/wiki/Kalachakra" title="Kalachakra">Kalachakra</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Time_perception" title="Time perception">Human experience</a><br />and <a href="/wiki/Time-use_research" title="Time-use research">use of time</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronemics" title="Chronemics">Chronemics</a></li> <li><a href="/wiki/Generation_time" title="Generation time">Generation time</a></li> <li><a href="/wiki/Mental_chronometry" title="Mental chronometry">Mental chronometry</a></li> <li><a href="/wiki/Duration_(music)" title="Duration (music)">Music</a> <ul><li><a href="/wiki/Tempo" title="Tempo">tempo</a></li> <li><a href="/wiki/Time_signature" title="Time signature">time signature</a></li></ul></li> <li><a href="/wiki/Rosy_retrospection" title="Rosy retrospection">Rosy retrospection</a></li> <li><a href="/wiki/Tense%E2%80%93aspect%E2%80%93mood" title="Tense–aspect–mood">Tense–aspect–mood</a></li> <li><a href="/wiki/Time_management" title="Time management">Time management</a></li> <li><a href="/wiki/Yesterday_(time)" title="Yesterday (time)">Yesterday</a> – <a href="/wiki/Present" title="Present">Today</a> – <a href="/wiki/Tomorrow_(time)" title="Tomorrow (time)">Tomorrow</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Time in <a href="/wiki/Science" title="Science">science</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:6.5em;font-weight:normal; text-align:center;"><a href="/wiki/Geology" title="Geology">Geology</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Geologic_time_scale" title="Geologic time scale">Geological time</a> <ul><li><a href="/wiki/Age_(geology)" class="mw-redirect" title="Age (geology)">age</a></li> <li><a href="/wiki/Chronozone" title="Chronozone">chron</a></li> <li><a href="/wiki/Eon_(geology)" class="mw-redirect" title="Eon (geology)">eon</a></li> <li><a href="/wiki/Epoch_(geology)" class="mw-redirect" title="Epoch (geology)">epoch</a></li> <li><a href="/wiki/Era_(geology)" class="mw-redirect" title="Era (geology)">era</a></li> <li><a href="/wiki/Geological_period" class="mw-redirect" title="Geological period">period</a></li></ul></li> <li><a href="/wiki/Geochronology" title="Geochronology">Geochronology</a></li> <li><a href="/wiki/Geological_history_of_Earth" title="Geological history of Earth">Geological history of Earth</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:6.5em;font-weight:normal; text-align:center;"><a href="/wiki/Time_in_physics" title="Time in physics">Physics</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Absolute_space_and_time" title="Absolute space and time">Absolute space and time</a></li> <li><a href="/wiki/Arrow_of_time" title="Arrow of time">Arrow of time</a></li> <li><a href="/wiki/Chronon" title="Chronon">Chronon</a></li> <li><a href="/wiki/Coordinate_time" title="Coordinate time">Coordinate time</a></li> <li><a href="/wiki/Instant" title="Instant">Instant</a></li> <li><a href="/wiki/Proper_time" title="Proper time">Proper time</a></li> <li><a href="/wiki/Spacetime" title="Spacetime">Spacetime</a></li> <li><a href="/wiki/Theory_of_relativity" title="Theory of relativity">Theory of relativity</a></li> <li><a href="/wiki/Time_domain" title="Time domain">Time domain</a></li> <li><a href="/wiki/Time_translation_symmetry" class="mw-redirect" title="Time translation symmetry">Time translation symmetry</a></li> <li><a href="/wiki/T-symmetry" title="T-symmetry">Time reversal symmetry</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:6.5em;font-weight:normal; text-align:center;">Other fields</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronological_dating" title="Chronological dating">Chronological dating</a></li> <li><a href="/wiki/Chronobiology" title="Chronobiology">Chronobiology</a> <ul><li><a href="/wiki/Circadian_rhythm" title="Circadian rhythm">Circadian rhythms</a></li></ul></li> <li><a href="/wiki/Chemical_clock" title="Chemical clock">Clock reaction</a></li> <li><a href="/wiki/Glottochronology" title="Glottochronology">Glottochronology</a></li> <li><a href="/wiki/Time_geography" title="Time geography">Time geography</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Leap_year" title="Leap year">Leap year</a></li> <li><a href="/wiki/Memory" title="Memory">Memory</a></li> <li><a href="/wiki/Moment_(unit)" title="Moment (unit)">Moment</a></li> <li><a href="/wiki/Space" title="Space">Space</a></li> <li><a href="/wiki/System_time" title="System time">System time</a></li> <li><i><a href="/wiki/Tempus_fugit" title="Tempus fugit">Tempus fugit</a></i></li> <li><a href="/wiki/Time_capsule" title="Time capsule">Time capsule</a></li> <li><a href="/wiki/Time_immemorial" title="Time immemorial">Time immemorial</a></li> <li><a href="/wiki/Time_travel" title="Time travel">Time travel</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <a href="/wiki/Category:Time" title="Category:Time">Category</a></li> <li><span class="noviewer" typeof="mw:File"><span title="Commons page"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/12px-Commons-logo.svg.png" decoding="async" width="12" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/18px-Commons-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/24px-Commons-logo.svg.png 2x" data-file-width="1024" data-file-height="1376" /></span></span> <a href="https://commons.wikimedia.org/wiki/Category:Time" class="extiw" title="commons:Category:Time">Commons</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Time_measurement_and_standards" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="3"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Time_measurement_and_standards" title="Template:Time measurement and standards"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Time_measurement_and_standards" title="Template talk:Time measurement and standards"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Time_measurement_and_standards" title="Special:EditPage/Template:Time measurement and standards"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Time_measurement_and_standards" style="font-size:114%;margin:0 4em"><a href="/wiki/Time" title="Time">Time measurement</a> and <a href="/wiki/Time_standard" title="Time standard">standards</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="3"><div> <ul><li><a href="/wiki/Chronometry" title="Chronometry">Chronometry</a></li> <li><a href="/wiki/Orders_of_magnitude_(time)" title="Orders of magnitude (time)">Orders of magnitude</a></li> <li><a href="/wiki/Time_metrology" class="mw-redirect" title="Time metrology">Metrology</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">International standards</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Coordinated_Universal_Time" title="Coordinated Universal Time">Coordinated Universal Time</a> <ul><li><a href="/wiki/UTC_offset" title="UTC offset">offset</a></li></ul></li> <li><a href="/wiki/Universal_Time" title="Universal Time">UT</a></li> <li><a href="/wiki/%CE%94T_(timekeeping)" title="ΔT (timekeeping)">ΔT</a></li> <li><a href="/wiki/DUT1" title="DUT1">DUT1</a></li> <li><a href="/wiki/International_Earth_Rotation_and_Reference_Systems_Service" title="International Earth Rotation and Reference Systems Service">International Earth Rotation and Reference Systems Service</a></li> <li><a href="/wiki/ISO_31-1" title="ISO 31-1">ISO 31-1</a></li> <li><a href="/wiki/ISO_8601" title="ISO 8601">ISO 8601</a></li> <li><a href="/wiki/International_Atomic_Time" title="International Atomic Time">International Atomic Time</a></li> <li><a href="/wiki/12-hour_clock" title="12-hour clock">12-hour clock</a></li> <li><a href="/wiki/24-hour_clock" title="24-hour clock">24-hour clock</a></li> <li><a href="/wiki/Barycentric_Coordinate_Time" title="Barycentric Coordinate Time">Barycentric Coordinate Time</a></li> <li><a href="/wiki/Barycentric_Dynamical_Time" title="Barycentric Dynamical Time">Barycentric Dynamical Time</a></li> <li><a href="/wiki/Civil_time" title="Civil time">Civil time</a></li> <li><a href="/wiki/Daylight_saving_time" title="Daylight saving time">Daylight saving time</a></li> <li><a href="/wiki/Geocentric_Coordinate_Time" title="Geocentric Coordinate Time">Geocentric Coordinate Time</a></li> <li><a href="/wiki/International_Date_Line" title="International Date Line">International Date Line</a></li> <li><a href="/wiki/IERS_Reference_Meridian" title="IERS Reference Meridian">IERS Reference Meridian</a></li> <li><a href="/wiki/Leap_second" title="Leap second">Leap second</a></li> <li><a href="/wiki/Solar_time" title="Solar time">Solar time</a></li> <li><a href="/wiki/Terrestrial_Time" title="Terrestrial Time">Terrestrial Time</a></li> <li><a href="/wiki/Time_zone" title="Time zone">Time zone</a></li> <li><a href="/wiki/180th_meridian" title="180th meridian">180th meridian</a></li></ul> </div></td><td class="noviewer navbox-image" rowspan="9" style="width:1px;padding:0 0 0 2px"><div><span typeof="mw:File"><a href="/wiki/Hourglass" title="Hourglass"><img alt="template illustration" src="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Marine_sandglass_MMM.jpg/75px-Marine_sandglass_MMM.jpg" decoding="async" width="75" height="175" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Marine_sandglass_MMM.jpg/113px-Marine_sandglass_MMM.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/70/Marine_sandglass_MMM.jpg/150px-Marine_sandglass_MMM.jpg 2x" data-file-width="1637" data-file-height="3819" /></a></span><br /><span typeof="mw:File"><a href="/wiki/Time_zone" title="Time zone"><img alt="template illustration" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/63/Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png/75px-Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png" decoding="async" width="75" height="152" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/63/Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png/113px-Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/63/Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png/150px-Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png 2x" data-file-width="496" data-file-height="1007" /></a></span></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Obsolete standards</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ephemeris_time" title="Ephemeris time">Ephemeris time</a></li> <li><a href="/wiki/Greenwich_Mean_Time" title="Greenwich Mean Time">Greenwich Mean Time</a></li> <li><a href="/wiki/Prime_meridian" title="Prime meridian">Prime meridian</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Time_in_physics" title="Time in physics">Time in physics</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Absolute_space_and_time" title="Absolute space and time">Absolute space and time</a></li> <li><a href="/wiki/Spacetime" title="Spacetime">Spacetime</a></li> <li><a href="/wiki/Chronon" title="Chronon">Chronon</a></li> <li><a href="/wiki/Continuous_signal" class="mw-redirect" title="Continuous signal">Continuous signal</a></li> <li><a href="/wiki/Coordinate_time" title="Coordinate time">Coordinate time</a></li> <li><a href="/wiki/Cosmological_decade" title="Cosmological decade">Cosmological decade</a></li> <li><a href="/wiki/Discrete_time_and_continuous_time" title="Discrete time and continuous time">Discrete time and continuous time</a></li> <li><a href="/wiki/Proper_time" title="Proper time">Proper time</a></li> <li><a href="/wiki/Theory_of_relativity" title="Theory of relativity">Theory of relativity</a></li> <li><a href="/wiki/Time_dilation" title="Time dilation">Time dilation</a></li> <li><a href="/wiki/Gravitational_time_dilation" title="Gravitational time dilation">Gravitational time dilation</a></li> <li><a href="/wiki/Time_domain" title="Time domain">Time domain</a></li> <li><a href="/wiki/Time-translation_symmetry" title="Time-translation symmetry">Time-translation symmetry</a></li> <li><a href="/wiki/T-symmetry" title="T-symmetry">T-symmetry</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Horology" class="mw-redirect" title="Horology">Horology</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Clock" title="Clock">Clock</a></li> <li><a href="/wiki/Astrarium" title="Astrarium">Astrarium</a></li> <li><a href="/wiki/Atomic_clock" title="Atomic clock">Atomic clock</a></li> <li><a href="/wiki/Complication_(horology)" title="Complication (horology)">Complication</a></li> <li><a href="/wiki/History_of_timekeeping_devices" title="History of timekeeping devices">History of timekeeping devices</a></li> <li><a href="/wiki/Hourglass" title="Hourglass">Hourglass</a></li> <li><a href="/wiki/Marine_chronometer" title="Marine chronometer">Marine chronometer</a></li> <li><a href="/wiki/Marine_sandglass" title="Marine sandglass">Marine sandglass</a></li> <li><a href="/wiki/Radio_clock" title="Radio clock">Radio clock</a></li> <li><a href="/wiki/Watch" title="Watch">Watch</a> <ul><li><a href="/wiki/Stopwatch" title="Stopwatch">stopwatch</a></li></ul></li> <li><a href="/wiki/Water_clock" title="Water clock">Water clock</a></li> <li><a href="/wiki/Sundial" title="Sundial">Sundial</a></li> <li><a href="/wiki/Dialing_scales" title="Dialing scales">Dialing scales</a></li> <li><a href="/wiki/Equation_of_time" title="Equation of time">Equation of time</a></li> <li><a href="/wiki/History_of_sundials" title="History of sundials">History of sundials</a></li> <li><a href="/wiki/Schema_for_horizontal_dials" title="Schema for horizontal dials">Sundial markup schema</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Calendar" title="Calendar">Calendar</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian</a></li> <li><a href="/wiki/Hebrew_calendar" title="Hebrew calendar">Hebrew</a></li> <li><a href="/wiki/Hindu_calendar" title="Hindu calendar">Hindu</a></li> <li><a href="/wiki/Holocene_calendar" title="Holocene calendar">Holocene</a></li> <li><a href="/wiki/Islamic_calendar" title="Islamic calendar">Islamic</a> (lunar Hijri)</li> <li><a href="/wiki/Julian_calendar" title="Julian calendar">Julian</a></li> <li><a href="/wiki/Solar_Hijri_calendar" title="Solar Hijri calendar">Solar Hijri</a></li> <li><a href="/wiki/Astronomical_year_numbering" title="Astronomical year numbering">Astronomical</a></li> <li><a href="/wiki/Dominical_letter" title="Dominical letter">Dominical letter</a></li> <li><a href="/wiki/Epact" title="Epact">Epact</a></li> <li><a href="/wiki/Equinox" title="Equinox">Equinox</a></li> <li><a href="/wiki/Intercalation_(timekeeping)" title="Intercalation (timekeeping)">Intercalation</a></li> <li><a href="/wiki/Julian_day" title="Julian day">Julian day</a></li> <li><a href="/wiki/Leap_year" title="Leap year">Leap year</a></li> <li><a href="/wiki/Lunar_calendar" title="Lunar calendar">Lunar</a></li> <li><a href="/wiki/Lunisolar_calendar" title="Lunisolar calendar">Lunisolar</a></li> <li><a href="/wiki/Solar_calendar" title="Solar calendar">Solar</a></li> <li><a href="/wiki/Solstice" title="Solstice">Solstice</a></li> <li><a href="/wiki/Tropical_year" title="Tropical year">Tropical year</a></li> <li><a href="/wiki/Determination_of_the_day_of_the_week" title="Determination of the day of the week">Weekday determination</a></li> <li><a href="/wiki/Names_of_the_days_of_the_week" title="Names of the days of the week">Weekday names</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Archaeology and geology</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronological_dating" title="Chronological dating">Chronological dating</a></li> <li><a href="/wiki/Geologic_time_scale" title="Geologic time scale">Geologic time scale</a></li> <li><a href="/wiki/International_Commission_on_Stratigraphy" title="International Commission on Stratigraphy">International Commission on Stratigraphy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Astronomical_chronology" title="Astronomical chronology">Astronomical chronology</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Galactic_year" title="Galactic year">Galactic year</a></li> <li><a href="/wiki/Nuclear_timescale" title="Nuclear timescale">Nuclear timescale</a></li> <li><a href="/wiki/Precession" title="Precession">Precession</a></li> <li><a href="/wiki/Sidereal_time" title="Sidereal time">Sidereal time</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other <a href="/wiki/Unit_of_time" title="Unit of time">units of time</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Instant" title="Instant">Instant</a></li> <li><a href="/wiki/Flick_(time)" title="Flick (time)">Flick</a></li> <li><a href="/wiki/Shake_(unit)" title="Shake (unit)">Shake</a></li> <li><a href="/wiki/Jiffy_(time)" title="Jiffy (time)">Jiffy</a></li> <li><a class="mw-selflink selflink">Second</a></li> <li><a href="/wiki/Minute" title="Minute">Minute</a></li> <li><a href="/wiki/Moment_(unit)" title="Moment (unit)">Moment</a></li> <li><a href="/wiki/Hour" title="Hour">Hour</a></li> <li><a href="/wiki/Day" title="Day">Day</a></li> <li><a href="/wiki/Week" title="Week">Week</a></li> <li><a href="/wiki/Fortnight" title="Fortnight">Fortnight</a></li> <li><a href="/wiki/Month" title="Month">Month</a></li> <li><a href="/wiki/Year" title="Year">Year</a></li> <li><a href="/wiki/Olympiad" title="Olympiad">Olympiad</a></li> <li><a href="/wiki/Lustrum" title="Lustrum">Lustrum</a></li> <li><a href="/wiki/Decade" title="Decade">Decade</a></li> <li><a href="/wiki/Century" title="Century">Century</a></li> <li><a href="/wiki/Saeculum" title="Saeculum">Saeculum</a></li> <li><a href="/wiki/Millennium" title="Millennium">Millennium</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related topics</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronology" title="Chronology">Chronology</a></li> <li><a href="/wiki/Duration_(philosophy)" title="Duration (philosophy)">Duration</a> <ul><li><a href="/wiki/Duration_(music)" title="Duration (music)">music</a></li></ul></li> <li><a href="/wiki/Mental_chronometry" title="Mental chronometry">Mental chronometry</a></li> <li><a href="/wiki/Decimal_time" title="Decimal time">Decimal time</a></li> <li><a href="/wiki/Metric_time" title="Metric time">Metric time</a></li> <li><a href="/wiki/System_time" title="System time">System time</a></li> <li><a href="/wiki/Time_metrology" class="mw-redirect" title="Time metrology">Time metrology</a></li> <li><a href="/wiki/Time_value_of_money" title="Time value of money">Time value of money</a></li> <li><a href="/wiki/Timekeeper" title="Timekeeper">Timekeeper</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="SI_units" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:SI_units" title="Template:SI units"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:SI_units" title="Template talk:SI units"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:SI_units" title="Special:EditPage/Template:SI units"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="SI_units" style="font-size:114%;margin:0 4em"><a href="/wiki/International_System_of_Units" title="International System of Units">SI units</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/SI_base_unit" title="SI base unit">Base units</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ampere" title="Ampere">ampere</a></li> <li><a href="/wiki/Candela" title="Candela">candela</a></li> <li><a href="/wiki/Kelvin" title="Kelvin">kelvin</a></li> <li><a href="/wiki/Kilogram" title="Kilogram">kilogram</a></li> <li><a href="/wiki/Metre" title="Metre">metre</a></li> <li><a href="/wiki/Mole_(unit)" title="Mole (unit)">mole</a></li> <li><a class="mw-selflink selflink">second</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/SI_derived_unit" title="SI derived unit">Derived units <br />with special names</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Becquerel" title="Becquerel">becquerel</a></li> <li><a href="/wiki/Coulomb" title="Coulomb">coulomb</a></li> <li><a href="/wiki/Celsius" title="Celsius">degree Celsius</a></li> <li><a href="/wiki/Farad" title="Farad">farad</a></li> <li><a href="/wiki/Gray_(unit)" title="Gray (unit)">gray</a></li> <li><a href="/wiki/Henry_(unit)" title="Henry (unit)">henry</a></li> <li><a href="/wiki/Hertz" title="Hertz">hertz</a></li> <li><a href="/wiki/Joule" title="Joule">joule</a></li> <li><a href="/wiki/Katal" title="Katal">katal</a></li> <li><a href="/wiki/Lumen_(unit)" title="Lumen (unit)">lumen</a></li> <li><a href="/wiki/Lux" title="Lux">lux</a></li> <li><a href="/wiki/Newton_(unit)" title="Newton (unit)">newton</a></li> <li><a href="/wiki/Ohm" title="Ohm">ohm</a></li> <li><a href="/wiki/Pascal_(unit)" title="Pascal (unit)">pascal</a></li> <li><a href="/wiki/Radian" title="Radian">radian</a></li> <li><a href="/wiki/Siemens_(unit)" title="Siemens (unit)">siemens</a></li> <li><a href="/wiki/Sievert" title="Sievert">sievert</a></li> <li><a href="/wiki/Steradian" title="Steradian">steradian</a></li> <li><a href="/wiki/Tesla_(unit)" title="Tesla (unit)">tesla</a></li> <li><a href="/wiki/Volt" title="Volt">volt</a></li> <li><a href="/wiki/Watt" title="Watt">watt</a></li> <li><a href="/wiki/Weber_(unit)" title="Weber (unit)">weber</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Non-SI_units_mentioned_in_the_SI" title="Non-SI units mentioned in the SI">Other accepted units</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Astronomical_unit" title="Astronomical unit">astronomical unit</a></li> <li><a href="/wiki/Dalton_(unit)" title="Dalton (unit)">dalton</a></li> <li><a href="/wiki/Day" title="Day">day</a></li> <li><a href="/wiki/Decibel" title="Decibel">decibel</a></li> <li><a href="/wiki/Degree_(angle)" title="Degree (angle)">degree of arc</a></li> <li><a href="/wiki/Electronvolt" title="Electronvolt">electronvolt</a></li> <li><a href="/wiki/Hectare" title="Hectare">hectare</a></li> <li><a href="/wiki/Hour" title="Hour">hour</a></li> <li><a href="/wiki/Litre" title="Litre">litre</a></li> <li><a href="/wiki/Minute" title="Minute">minute</a></li> <li><a href="/wiki/Minute_and_second_of_arc" title="Minute and second of arc">minute and second of arc</a></li> <li><a href="/wiki/Neper" title="Neper">neper</a></li> <li><a href="/wiki/Tonne" title="Tonne">tonne</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">See also</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Conversion_of_units" title="Conversion of units">Conversion of units</a></li> <li><a href="/wiki/Metric_prefix" title="Metric prefix">Metric prefixes</a></li> <li><a href="/wiki/Historical_definitions_of_the_SI_base_units" title="Historical definitions of the SI base units">Historical definitions of the SI base units</a></li> <li><a href="/wiki/2019_revision_of_the_SI" title="2019 revision of the SI">2019 revision of the SI</a></li> <li><a href="/wiki/System_of_units_of_measurement" title="System of units of measurement">System of units of measurement</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <a href="/wiki/Category:SI_units" title="Category:SI units">Category</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Orders_of_magnitude_of_time" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Orders_of_magnitude_(time)" title="Template:Orders of magnitude (time)"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Orders_of_magnitude_(time)" title="Template talk:Orders of magnitude (time)"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Orders_of_magnitude_(time)" title="Special:EditPage/Template:Orders of magnitude (time)"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Orders_of_magnitude_of_time" style="font-size:114%;margin:0 4em"><a href="/wiki/Orders_of_magnitude_(time)" title="Orders of magnitude (time)">Orders of magnitude of time</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div>by <a href="/wiki/Exponentiation" title="Exponentiation">powers</a> of ten</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Negative powers</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Orders_of_magnitude_(time)" title="Orders of magnitude (time)"><1 attosecond</a></li> <li><a href="/wiki/Attosecond" title="Attosecond">attosecond</a></li> <li><a href="/wiki/Femtosecond" title="Femtosecond">femtosecond</a></li> <li><a href="/wiki/Picosecond" title="Picosecond">picosecond</a></li> <li><a href="/wiki/Nanosecond" title="Nanosecond">nanosecond</a></li> <li><a href="/wiki/Microsecond" title="Microsecond">microsecond</a></li> <li><a href="/wiki/Millisecond" title="Millisecond">millisecond</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Positive powers</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a class="mw-selflink selflink">second</a></li> <li><a href="/wiki/Kilosecond" class="mw-redirect" title="Kilosecond">kilosecond</a></li> <li><a href="/wiki/Megasecond" class="mw-redirect" title="Megasecond">megasecond</a></li> <li><a href="/wiki/Gigasecond" class="mw-redirect" title="Gigasecond">gigasecond</a></li> <li><a href="/wiki/Terasecond_and_longer" class="mw-redirect" title="Terasecond and longer">terasecond and longer</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="CGS_units" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:CGS_units" title="Template:CGS units"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:CGS_units" title="Template talk:CGS units"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:CGS_units" title="Special:EditPage/Template:CGS units"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="CGS_units" style="font-size:114%;margin:0 4em"><a href="/wiki/Centimetre%E2%80%93gram%E2%80%93second_system_of_units" title="Centimetre–gram–second system of units">CGS units</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Base units</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Centimetre" title="Centimetre">centimetre</a></li> <li><a href="/wiki/Gram" title="Gram">gram</a></li> <li><a class="mw-selflink selflink">second</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Derived non EM units</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Barye" title="Barye">barye</a></li> <li><a href="/wiki/Dyne" title="Dyne">dyne</a></li> <li><a href="/wiki/Erg" title="Erg">erg</a></li> <li><a href="/wiki/Gal_(unit)" title="Gal (unit)">gal</a></li> <li><a href="/wiki/Kelvin" title="Kelvin">kelvin</a></li> <li><a href="/wiki/Poise_(unit)" title="Poise (unit)">poise</a></li> <li><a href="/wiki/Kayser_(unit)" class="mw-redirect" title="Kayser (unit)">kayser</a></li> <li><a href="/wiki/Phot" title="Phot">phot</a></li> <li><a href="/wiki/Stilb_(unit)" title="Stilb (unit)">stilb</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Derived EMU units</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Abampere" title="Abampere">abampere</a> (<a href="/wiki/Biot_(unit)" class="mw-redirect" title="Biot (unit)">biot</a>)</li> <li><a href="/wiki/Abcoulomb" title="Abcoulomb">abcoulomb</a></li> <li><a href="/wiki/Abhenry" title="Abhenry">abhenry</a></li> <li><a href="/wiki/Abmho" title="Abmho">abmho</a></li> <li><a href="/wiki/Abohm" title="Abohm">abohm</a></li> <li><a href="/wiki/Abvolt" title="Abvolt">abvolt</a></li> <li><a href="/wiki/Gauss_(unit)" title="Gauss (unit)">gauss</a></li> <li><a href="/wiki/Gilbert_(unit)" title="Gilbert (unit)">gilbert</a></li> <li><a href="/wiki/Maxwell_(unit)" title="Maxwell (unit)">maxwell</a></li> <li><a href="/wiki/Oersted" title="Oersted">oersted</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Derived ESU units</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Statampere" title="Statampere">statampere</a></li> <li><a href="/wiki/Statcoulomb" title="Statcoulomb">statcoulomb</a></li> <li><a href="/wiki/Statmho" title="Statmho">statmho</a></li> <li><a href="/wiki/Statohm" title="Statohm">statohm</a></li> <li><a href="/wiki/Statvolt" title="Statvolt">statvolt</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox authority-control" aria-label="Navbox" style="padding:3px"><table class="nowraplinks hlist navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Help:Authority_control" title="Help:Authority control">Authority control databases</a>: National <span class="mw-valign-text-top noprint" typeof="mw:File/Frameless"><a href="https://www.wikidata.org/wiki/Q11574#identifiers" title="Edit this at Wikidata"><img alt="Edit this at Wikidata" src="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/10px-OOjs_UI_icon_edit-ltr-progressive.svg.png" decoding="async" width="10" height="10" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/15px-OOjs_UI_icon_edit-ltr-progressive.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/20px-OOjs_UI_icon_edit-ltr-progressive.svg.png 2x" data-file-width="20" data-file-height="20" /></a></span></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"><ul><li><span class="uid"><a rel="nofollow" class="external text" href="https://d-nb.info/gnd/1188905376">Germany</a></span></li></ul></div></td></tr></tbody></table></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=Second&oldid=1256553341">https://en.wikipedia.org/w/index.php?title=Second&oldid=1256553341</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Help:Category" title="Help:Category">Categories</a>: <ul><li><a href="/wiki/Category:Centimetre%E2%80%93gram%E2%80%93second_system_of_units" title="Category:Centimetre–gram–second system of units">Centimetre–gram–second system of units</a></li><li><a href="/wiki/Category:Orders_of_magnitude_(time)" title="Category:Orders of magnitude (time)">Orders of magnitude (time)</a></li><li><a href="/wiki/Category:SI_base_units" title="Category:SI base units">SI base units</a></li><li><a href="/wiki/Category:Units_of_time" title="Category:Units of time">Units of time</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:Articles_with_short_description" title="Category:Articles with short description">Articles with short description</a></li><li><a href="/wiki/Category:Short_description_is_different_from_Wikidata" title="Category:Short description is different from Wikidata">Short description is different from Wikidata</a></li><li><a href="/wiki/Category:Use_mdy_dates_from_September_2016" title="Category:Use mdy dates from September 2016">Use mdy dates from September 2016</a></li><li><a href="/wiki/Category:Use_American_English_from_September_2020" title="Category:Use American English from September 2020">Use American English from September 2020</a></li><li><a href="/wiki/Category:All_Wikipedia_articles_written_in_American_English" title="Category:All Wikipedia articles written in American English">All Wikipedia articles written in American English</a></li><li><a href="/wiki/Category:Articles_containing_Latin-language_text" title="Category:Articles containing Latin-language text">Articles containing Latin-language text</a></li><li><a href="/wiki/Category:Commons_link_from_Wikidata" title="Category:Commons link from Wikidata">Commons link from Wikidata</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 10 November 2024, at 13:46<span class="anonymous-show"> (UTC)</span>.</li> <li id="footer-info-copyright">Text is available under the <a href="/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License" title="Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License">Creative Commons Attribution-ShareAlike 4.0 License</a>; additional terms may apply. By using this site, you agree to the <a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Terms_of_Use" class="extiw" title="foundation:Special:MyLanguage/Policy:Terms of Use">Terms of Use</a> and <a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Privacy_policy" class="extiw" title="foundation:Special:MyLanguage/Policy:Privacy policy">Privacy Policy</a>. Wikipedia® is a registered trademark of the <a rel="nofollow" class="external text" href="https://wikimediafoundation.org/">Wikimedia Foundation, Inc.</a>, a non-profit organization.</li> </ul> <ul id="footer-places"> <li id="footer-places-privacy"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Privacy_policy">Privacy policy</a></li> <li id="footer-places-about"><a href="/wiki/Wikipedia:About">About Wikipedia</a></li> <li id="footer-places-disclaimers"><a href="/wiki/Wikipedia:General_disclaimer">Disclaimers</a></li> <li id="footer-places-contact"><a href="//en.wikipedia.org/wiki/Wikipedia:Contact_us">Contact Wikipedia</a></li> <li id="footer-places-wm-codeofconduct"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Universal_Code_of_Conduct">Code of Conduct</a></li> <li id="footer-places-developers"><a href="https://developer.wikimedia.org">Developers</a></li> <li id="footer-places-statslink"><a href="https://stats.wikimedia.org/#/en.wikipedia.org">Statistics</a></li> <li id="footer-places-cookiestatement"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Cookie_statement">Cookie statement</a></li> <li id="footer-places-mobileview"><a href="//en.m.wikipedia.org/w/index.php?title=Second&mobileaction=toggle_view_mobile" class="noprint stopMobileRedirectToggle">Mobile view</a></li> </ul> <ul id="footer-icons" class="noprint"> <li id="footer-copyrightico"><a href="https://wikimediafoundation.org/" class="cdx-button cdx-button--fake-button cdx-button--size-large cdx-button--fake-button--enabled"><img src="/static/images/footer/wikimedia-button.svg" width="84" height="29" alt="Wikimedia Foundation" loading="lazy"></a></li> <li id="footer-poweredbyico"><a href="https://www.mediawiki.org/" class="cdx-button cdx-button--fake-button cdx-button--size-large cdx-button--fake-button--enabled"><img src="/w/resources/assets/poweredby_mediawiki.svg" alt="Powered by MediaWiki" width="88" height="31" loading="lazy"></a></li> </ul> </footer> </div> </div> </div> <div class="vector-settings" id="p-dock-bottom"> <ul></ul> </div><script>(RLQ=window.RLQ||[]).push(function(){mw.config.set({"wgHostname":"mw-web.codfw.main-688fc9465-l82hz","wgBackendResponseTime":193,"wgPageParseReport":{"limitreport":{"cputime":"0.845","walltime":"1.169","ppvisitednodes":{"value":4916,"limit":1000000},"postexpandincludesize":{"value":115288,"limit":2097152},"templateargumentsize":{"value":3042,"limit":2097152},"expansiondepth":{"value":18,"limit":100},"expensivefunctioncount":{"value":9,"limit":500},"unstrip-depth":{"value":1,"limit":20},"unstrip-size":{"value":136803,"limit":5000000},"entityaccesscount":{"value":1,"limit":400},"timingprofile":["100.00% 954.868 1 -total"," 21.80% 208.134 2 Template:Reflist"," 13.12% 125.323 2 Template:Lang"," 12.29% 117.379 1 Template:Time_topics"," 10.84% 103.509 7 Template:Cite_web"," 8.46% 80.793 2 Template:Sister_project"," 8.25% 78.764 2 Template:Side_box"," 7.55% 72.126 1 Template:Short_description"," 6.21% 59.328 7 Template:Rp"," 6.17% 58.922 1 Template:Commons"]},"scribunto":{"limitreport-timeusage":{"value":"0.490","limit":"10.000"},"limitreport-memusage":{"value":18881147,"limit":52428800}},"cachereport":{"origin":"mw-api-ext.codfw.main-744c7589dd-pfwbs","timestamp":"20241125143133","ttl":2592000,"transientcontent":false}}});});</script> <script type="application/ld+json">{"@context":"https:\/\/schema.org","@type":"Article","name":"Second","url":"https:\/\/en.wikipedia.org\/wiki\/Second","sameAs":"http:\/\/www.wikidata.org\/entity\/Q11574","mainEntity":"http:\/\/www.wikidata.org\/entity\/Q11574","author":{"@type":"Organization","name":"Contributors to Wikimedia projects"},"publisher":{"@type":"Organization","name":"Wikimedia Foundation, Inc.","logo":{"@type":"ImageObject","url":"https:\/\/www.wikimedia.org\/static\/images\/wmf-hor-googpub.png"}},"datePublished":"2001-07-27T08:02:47Z","dateModified":"2024-11-10T13:46:27Z","image":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/1\/15\/Clock-pendulum.gif","headline":"SI unit of time, defined as 9\u2009192\u2009631\u2009770 periods of the ground-state hyperfine transitions of caesium-133"}</script> </body> </html>