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class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>Earth rotation angle</span> </div> </a> <ul id="toc-Earth_rotation_angle-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Mean_and_apparent_varieties" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Mean_and_apparent_varieties"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Mean and apparent varieties</span> </div> </a> <ul id="toc-Mean_and_apparent_varieties-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Relationship_between_solar_time_and_sidereal_time_intervals" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Relationship_between_solar_time_and_sidereal_time_intervals"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>Relationship between solar time and sidereal time intervals</span> </div> </a> <ul id="toc-Relationship_between_solar_time_and_sidereal_time_intervals-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Sidereal_days_compared_to_solar_days_on_other_planets" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Sidereal_days_compared_to_solar_days_on_other_planets"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Sidereal days compared to solar days on other planets</span> </div> </a> <ul id="toc-Sidereal_days_compared_to_solar_days_on_other_planets-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">5</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Citations" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Citations"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Citations</span> </div> </a> <ul id="toc-Citations-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">7</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">8</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">Sidereal time</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 55 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-55" 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">55 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%AA%D9%88%D9%82%D9%8A%D8%AA_%D9%81%D9%84%D9%83%D9%8A" title="توقيت فلكي – Arabic" lang="ar" hreflang="ar" data-title="توقيت فلكي" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ast mw-list-item"><a href="https://ast.wikipedia.org/wiki/Tiempu_sid%C3%A9reo" title="Tiempu sidéreo – Asturian" lang="ast" hreflang="ast" data-title="Tiempu sidéreo" data-language-autonym="Asturianu" data-language-local-name="Asturian" class="interlanguage-link-target"><span>Asturianu</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/Ulduz_vaxt%C4%B1" title="Ulduz vaxtı – Azerbaijani" lang="az" hreflang="az" data-title="Ulduz vaxtı" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%A8%E0%A6%95%E0%A7%8D%E0%A6%B7%E0%A6%A4%E0%A7%8D%E0%A6%B0_%E0%A6%B8%E0%A6%AE%E0%A6%AF%E0%A6%BC" title="নক্ষত্র সময় – Bangla" lang="bn" hreflang="bn" data-title="নক্ষত্র সময়" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-bh mw-list-item"><a href="https://bh.wikipedia.org/wiki/%E0%A4%A8%E0%A4%BE%E0%A4%95%E0%A5%8D%E0%A4%B7%E0%A4%A4%E0%A5%8D%E0%A4%B0_%E0%A4%B8%E0%A4%AE%E0%A4%AF" title="नाक्षत्र समय – Bhojpuri" lang="bh" hreflang="bh" data-title="नाक्षत्र समय" data-language-autonym="भोजपुरी" data-language-local-name="Bhojpuri" class="interlanguage-link-target"><span>भोजपुरी</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%97%D0%B2%D0%B5%D0%B7%D0%B4%D0%B5%D0%BD_%D0%B4%D0%B5%D0%BD" title="Звезден ден – Bulgarian" lang="bg" hreflang="bg" data-title="Звезден ден" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Temps_sideri" title="Temps sideri – Catalan" lang="ca" hreflang="ca" data-title="Temps sideri" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Hv%C4%9Bzdn%C3%BD_%C4%8Das" title="Hvězdný čas – Czech" lang="cs" hreflang="cs" data-title="Hvězdný čas" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Sternzeit" title="Sternzeit – German" lang="de" hreflang="de" data-title="Sternzeit" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Tiempo_sid%C3%A9reo" title="Tiempo sidéreo – Spanish" lang="es" hreflang="es" data-title="Tiempo sidéreo" 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/Sidera_tempo" title="Sidera tempo – Esperanto" lang="eo" hreflang="eo" data-title="Sidera tempo" 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/Denbora_sideral" title="Denbora sideral – Basque" lang="eu" hreflang="eu" data-title="Denbora sideral" 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%B2%D9%85%D8%A7%D9%86_%D9%86%D8%AC%D9%88%D9%85%DB%8C" title="زمان نجومی – Persian" lang="fa" hreflang="fa" data-title="زمان نجومی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Temps_sid%C3%A9ral" title="Temps sidéral – French" lang="fr" hreflang="fr" data-title="Temps sidéral" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Tempo_sideral" title="Tempo sideral – Galician" lang="gl" hreflang="gl" data-title="Tempo sideral" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%ED%95%AD%EC%84%B1%EC%8B%9C" title="항성시 – Korean" lang="ko" hreflang="ko" data-title="항성시" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%A8%E0%A4%BE%E0%A4%95%E0%A5%8D%E0%A4%B7%E0%A4%A4%E0%A5%8D%E0%A4%B0_%E0%A4%B8%E0%A4%AE%E0%A4%AF" title="नाक्षत्र समय – Hindi" lang="hi" hreflang="hi" data-title="नाक्षत्र समय" 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/Sideri%C4%8Dki_dan" title="Siderički dan – Croatian" lang="hr" hreflang="hr" data-title="Siderički dan" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-ig mw-list-item"><a href="https://ig.wikipedia.org/wiki/Oge_ihu_igwe" title="Oge ihu igwe – Igbo" lang="ig" hreflang="ig" data-title="Oge ihu igwe" data-language-autonym="Igbo" data-language-local-name="Igbo" class="interlanguage-link-target"><span>Igbo</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Waktu_sideris" title="Waktu sideris – Indonesian" lang="id" hreflang="id" data-title="Waktu sideris" 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/Tempore_sideral" title="Tempore sideral – Interlingua" lang="ia" hreflang="ia" data-title="Tempore sideral" data-language-autonym="Interlingua" data-language-local-name="Interlingua" class="interlanguage-link-target"><span>Interlingua</span></a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/Stj%C3%B6rnut%C3%ADmi" title="Stjörnutími – Icelandic" lang="is" hreflang="is" data-title="Stjörnutími" 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/Tempo_siderale" title="Tempo siderale – Italian" lang="it" hreflang="it" data-title="Tempo siderale" 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%99%D7%9E%D7%9E%D7%94_%D7%9B%D7%95%D7%9B%D7%91%D7%99%D7%AA" title="יממה כוכבית – Hebrew" lang="he" hreflang="he" data-title="יממה כוכבית" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/%D0%96%D2%B1%D0%BB%D0%B4%D1%8B%D0%B7%D0%B4%D1%8B%D2%9B_%D1%83%D0%B0%D2%9B%D1%8B%D1%82" title="Жұлдыздық уақыт – Kazakh" lang="kk" hreflang="kk" data-title="Жұлдыздық уақыт" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-sw mw-list-item"><a href="https://sw.wikipedia.org/wiki/Siku_ya_nyota" title="Siku ya nyota – Swahili" lang="sw" hreflang="sw" data-title="Siku ya nyota" data-language-autonym="Kiswahili" data-language-local-name="Swahili" class="interlanguage-link-target"><span>Kiswahili</span></a></li><li class="interlanguage-link interwiki-la mw-list-item"><a href="https://la.wikipedia.org/wiki/Dies_sideralis" title="Dies sideralis – Latin" lang="la" hreflang="la" data-title="Dies sideralis" data-language-autonym="Latina" data-language-local-name="Latin" class="interlanguage-link-target"><span>Latina</span></a></li><li class="interlanguage-link interwiki-lb mw-list-item"><a href="https://lb.wikipedia.org/wiki/Sideresch_%C3%8Bmlafz%C3%A4it" title="Sideresch Ëmlafzäit – Luxembourgish" lang="lb" hreflang="lb" data-title="Sideresch Ëmlafzäit" 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/%C5%BDvaig%C5%BEdinis_laikas" title="Žvaigždinis laikas – Lithuanian" lang="lt" hreflang="lt" data-title="Žvaigždinis laikas" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/Sziderikus_id%C5%91" title="Sziderikus idő – Hungarian" lang="hu" hreflang="hu" data-title="Sziderikus idő" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%85%D0%B2%D0%B5%D0%B7%D0%B4%D0%B5%D0%BD%D0%BE_%D0%B2%D1%80%D0%B5%D0%BC%D0%B5" title="Ѕвездено време – Macedonian" lang="mk" hreflang="mk" data-title="Ѕвездено време" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%B8%E0%B5%88%E0%B4%A1%E0%B5%80%E0%B4%B0%E0%B4%BF%E0%B4%AF%E0%B5%BD_%E0%B4%9F%E0%B5%88%E0%B4%82" title="സൈഡീരിയൽ ടൈം – Malayalam" lang="ml" hreflang="ml" data-title="സൈഡീരിയൽ ടൈം" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Waktu_ikut_bintang" title="Waktu ikut bintang – Malay" lang="ms" hreflang="ms" data-title="Waktu ikut bintang" 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-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Sterrentijd" title="Sterrentijd – Dutch" lang="nl" hreflang="nl" data-title="Sterrentijd" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E6%81%92%E6%98%9F%E6%99%82" title="恒星時 – Japanese" lang="ja" hreflang="ja" data-title="恒星時" 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-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Siderisk_tid" title="Siderisk tid – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Siderisk tid" 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/Stjerned%C3%B8gn" title="Stjernedøgn – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Stjernedøgn" 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/Jorn_sideral" title="Jorn sideral – Occitan" lang="oc" hreflang="oc" data-title="Jorn sideral" data-language-autonym="Occitan" data-language-local-name="Occitan" class="interlanguage-link-target"><span>Occitan</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Czas_gwiazdowy" title="Czas gwiazdowy – Polish" lang="pl" hreflang="pl" data-title="Czas gwiazdowy" 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/Tempo_sideral" title="Tempo sideral – Portuguese" lang="pt" hreflang="pt" data-title="Tempo sideral" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Timp_sideral" title="Timp sideral – Romanian" lang="ro" hreflang="ro" data-title="Timp sideral" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%97%D0%B2%D1%91%D0%B7%D0%B4%D0%BD%D0%BE%D0%B5_%D0%B2%D1%80%D0%B5%D0%BC%D1%8F" title="Звёздное время – Russian" lang="ru" hreflang="ru" data-title="Звёздное время" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Sidereal_time" title="Sidereal time – Simple English" lang="en-simple" hreflang="en-simple" data-title="Sidereal time" 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-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Hviezdny_%C4%8Das" title="Hviezdny čas – Slovak" lang="sk" hreflang="sk" data-title="Hviezdny čas" data-language-autonym="Slovenčina" data-language-local-name="Slovak" 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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">Timekeeping system on Earth relative to the celestial sphere</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 astronomical time system. For the novel, see <a href="/wiki/Christopher_Meredith#Publications" title="Christopher Meredith">Sidereal Time</a>.</div> <p class="mw-empty-elt"> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Sidereal_Day_poster.png" class="mw-file-description"><img alt="A sidereal day is 1 Earth rotation relative to the stars; a solar day is 1 Earth rotation relative to the Sun. The Earth rotates 366 times per 'normal' 365-day year relative to the stars, so Earth's sidereal day is 4 minutes shorter than Earth's solar day." src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Sidereal_Day_poster.png/390px-Sidereal_Day_poster.png" decoding="async" width="390" height="244" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Sidereal_Day_poster.png/585px-Sidereal_Day_poster.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Sidereal_Day_poster.png/780px-Sidereal_Day_poster.png 2x" data-file-width="1920" data-file-height="1200" /></a><figcaption>Picture of a poster clarifying the difference between a sidereal day and the more conventional <a href="/wiki/Synodic_day" title="Synodic day">solar day</a></figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><span><video id="mwe_player_0" poster="//upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Sidereal_Day_versus_Solar_Day.webm/220px--Sidereal_Day_versus_Solar_Day.webm.jpg" controls="" preload="none" data-mw-tmh="" class="mw-file-element" width="220" height="124" data-durationhint="34" data-mwtitle="Sidereal_Day_versus_Solar_Day.webm" data-mwprovider="wikimediacommons" resource="/wiki/File:Sidereal_Day_versus_Solar_Day.webm"><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/9/9e/Sidereal_Day_versus_Solar_Day.webm/Sidereal_Day_versus_Solar_Day.webm.480p.vp9.webm" type="video/webm; codecs="vp9, opus"" data-transcodekey="480p.vp9.webm" data-width="854" data-height="480" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/9/9e/Sidereal_Day_versus_Solar_Day.webm/Sidereal_Day_versus_Solar_Day.webm.720p.vp9.webm" type="video/webm; codecs="vp9, opus"" data-transcodekey="720p.vp9.webm" data-width="1280" data-height="720" /><source src="//upload.wikimedia.org/wikipedia/commons/9/9e/Sidereal_Day_versus_Solar_Day.webm" type="video/webm; codecs="vp9"" data-width="1920" data-height="1080" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/9/9e/Sidereal_Day_versus_Solar_Day.webm/Sidereal_Day_versus_Solar_Day.webm.1080p.vp9.webm" type="video/webm; codecs="vp9, opus"" data-transcodekey="1080p.vp9.webm" data-width="1920" data-height="1080" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/9/9e/Sidereal_Day_versus_Solar_Day.webm/Sidereal_Day_versus_Solar_Day.webm.240p.vp9.webm" type="video/webm; codecs="vp9, opus"" data-transcodekey="240p.vp9.webm" data-width="426" data-height="240" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/9/9e/Sidereal_Day_versus_Solar_Day.webm/Sidereal_Day_versus_Solar_Day.webm.360p.vp9.webm" type="video/webm; codecs="vp9, opus"" data-transcodekey="360p.vp9.webm" data-width="640" data-height="360" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/9/9e/Sidereal_Day_versus_Solar_Day.webm/Sidereal_Day_versus_Solar_Day.webm.360p.webm" type="video/webm; codecs="vp8, vorbis"" data-transcodekey="360p.webm" data-width="640" data-height="360" /></video></span><figcaption>Animation showing the difference between a sidereal day and a <a href="/wiki/Synodic_day" title="Synodic day">solar day</a></figcaption></figure> <p><b>Sidereal time</b> ("sidereal" pronounced <span class="rt-commentedText nowrap"><span class="IPA nopopups noexcerpt" lang="en-fonipa"><a href="/wiki/Help:IPA/English" title="Help:IPA/English">/<span style="border-bottom:1px dotted"><span title="'s' in 'sigh'">s</span><span title="/aɪ/: 'i' in 'tide'">aɪ</span><span title="/ˈ/: primary stress follows">ˈ</span><span title="'d' in 'dye'">d</span><span title="/ɪər/: 'ear' in 'near'">ɪər</span><span title="/i/: 'y' in 'happy'">i</span><span title="/əl/: 'le' in 'bottle'">əl</span></span>,<span class="wrap"> </span><span style="border-bottom:1px dotted"><span title="'s' in 'sigh'">s</span><span title="/ə/: 'a' in 'about'">ə</span></span>-/</a></span></span> <a href="/wiki/Help:Pronunciation_respelling_key" title="Help:Pronunciation respelling key"><i title="English pronunciation respelling">sy-<span style="font-size:90%">DEER</span>-ee-əl, sə-</i></a>) is a system of <a href="/wiki/Timekeeper" title="Timekeeper">timekeeping</a> used especially by <a href="/wiki/Astronomer" title="Astronomer">astronomers</a>. Using sidereal time and the <a href="/wiki/Celestial_coordinate_system" class="mw-redirect" title="Celestial coordinate system">celestial coordinate system</a>, it is easy to locate the positions of <a href="/wiki/Astronomical_object" title="Astronomical object">celestial objects</a> in the <a href="/wiki/Night_sky" title="Night sky">night sky</a>. Sidereal time is a "time scale that is based on <a href="/wiki/Earth%27s_rotation" title="Earth's rotation">Earth's rate of rotation</a> measured relative to the <a href="/wiki/Fixed_stars" title="Fixed stars">fixed stars</a>".<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p><p>Viewed from the same <a href="/wiki/Location" title="Location">location</a>, a star seen at one position in the sky will be seen at the same position on another night at the same time of day (or night), if the day is defined as a <b>sidereal day</b> (also known as the <b>sidereal rotation period</b>). This is similar to how the time kept by a <a href="/wiki/Sundial" title="Sundial">sundial</a> (<a href="/wiki/Solar_time" title="Solar time">Solar time</a>) can be used to find the location of the <a href="/wiki/Sun" title="Sun">Sun</a>. Just as the Sun and <a href="/wiki/Moon" title="Moon">Moon</a> appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earth's rotation about its polar axis: solar time is reckoned according to the position of the Sun in the sky while sidereal time is based approximately on the position of the fixed stars on the theoretical celestial sphere. </p><p>More exactly, sidereal time is the angle, measured along the <a href="/wiki/Celestial_equator" title="Celestial equator">celestial equator</a>, from the observer's <a href="/wiki/Meridian_(astronomy)" title="Meridian (astronomy)">meridian</a> to the <a href="/wiki/Great_circle" title="Great circle">great circle</a> that passes through the <a href="/wiki/March_equinox" title="March equinox">March equinox</a> (the northern hemisphere's vernal equinox) and both <a href="/wiki/Celestial_pole" title="Celestial pole">celestial poles</a>, and is usually expressed in hours, minutes, and seconds. (In the context of sidereal time, "March equinox" or "equinox" or "first point of Aries" is currently a direction, from the center of the Earth along the line formed by the intersection of the Earth's equator and the Earth's orbit around the Sun, toward the constellation Pisces; during ancient times it was toward the constellation Aries.) <sup id="cite_ref-FOOTNOTEUrbanSeidelmann2013"Glossary"_s.v._hour_angle,_hour_circle,_sidereal_time_2-0" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann2013"Glossary"_s.v._hour_angle,_hour_circle,_sidereal_time-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> Common time on a typical clock (using <a href="/wiki/Solar_time#Mean_solar_time" title="Solar time">mean Solar time</a>) measures a slightly longer cycle, affected not only by Earth's axial rotation but also by Earth's orbit around the Sun. </p><p>The March equinox itself <a href="/wiki/Axial_precession" title="Axial precession">precesses</a> slowly westward relative to the fixed stars, completing one revolution in about 25,800 years, so the misnamed "sidereal" day ("sidereal" is derived from the Latin <i>sidus</i> meaning "star") is 0.0084 seconds shorter than the <a href="/wiki/Stellar_day" class="mw-redirect" title="Stellar day">stellar day</a>, Earth's actual period of rotation relative to the fixed stars.<sup id="cite_ref-FOOTNOTEUrbanSeidelmann201378_3-0" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann201378-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> The slightly longer stellar period is measured as the <a href="/wiki/Earth_rotation_angle" class="mw-redirect" title="Earth rotation angle">Earth rotation angle</a> (ERA), formerly the stellar angle.<sup id="cite_ref-FOOTNOTEIERS2013_4-0" class="reference"><a href="#cite_note-FOOTNOTEIERS2013-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> An increase of 360° in the ERA is a full rotation of the Earth. </p><p><span class="anchor" id="Sidereal_day"></span>A sidereal day on Earth is approximately 86164.0905 <a href="/wiki/Second" title="Second">seconds</a> (23 h 56 min 4.0905 s or 23.9344696 h). (Seconds are defined as per <a href="/wiki/International_System_of_Units" title="International System of Units">International System of Units</a> and are not to be confused with <a href="/wiki/Ephemeris_second" class="mw-redirect" title="Ephemeris second">ephemeris seconds</a>.) Each day, the sidereal time at any given place and time will be about four minutes shorter than local <a href="/wiki/Civil_time" title="Civil time">civil time</a> (which is based on solar time), so that for a complete year the number of sidereal "days" is one more than the number of solar days. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Comparison_to_solar_time">Comparison to solar time</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Sidereal_time&action=edit&section=1" title="Edit section: Comparison to solar time"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Sidereal_time.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Sidereal_time.svg/280px-Sidereal_time.svg.png" decoding="async" width="280" height="443" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Sidereal_time.svg/420px-Sidereal_time.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Sidereal_time.svg/560px-Sidereal_time.svg.png 2x" data-file-width="337" data-file-height="533" /></a><figcaption>Sidereal time vs solar time. <b>Above left</b>: a distant star (the small orange star) and the Sun are at <a href="/wiki/Culmination" title="Culmination">culmination</a>, on the local meridian <b>m</b>. <i>Centre</i>: only the distant star is at culmination (a mean <a href="/wiki/Sidereal_day" class="mw-redirect" title="Sidereal day">sidereal day</a>). <i>Right</i>: a few minutes later the Sun is on the local meridian again. A <a href="/wiki/Solar_day" class="mw-redirect" title="Solar day">solar day</a> is complete.</figcaption></figure> <p><a href="/wiki/Solar_time" title="Solar time">Solar time</a> is measured by the apparent <a href="/wiki/Diurnal_motion" title="Diurnal motion">diurnal motion</a> of the Sun. Local noon in apparent solar time is the moment when the Sun is exactly due south or north (depending on the observer's latitude and the season). A mean solar day (what we normally measure as a "day") is the average time between local solar noons ("average" since this varies slightly over a year). </p><p>Earth makes one rotation around its axis each sidereal day; during that time it moves a short distance (about 1°) along its orbit around the Sun. So after a sidereal day has passed, Earth still needs to rotate slightly more before the Sun reaches local noon according to solar time. A mean solar day is, therefore, nearly 4 minutes longer than a sidereal day. </p><p>The stars are so far away that Earth's movement along its orbit makes nearly no difference to their apparent direction (except for the nearest stars if measured with extreme accuracy; see <a href="/wiki/Parallax" title="Parallax">parallax</a>), and so they return to their highest point at the same time each sidereal day. </p><p>Another way to understand this difference is to notice that, relative to the stars, as viewed from Earth, the position of the Sun at the same time each day appears to move around Earth once per year. A year has about 36<b>5</b>.24 solar days but 36<b>6</b>.24 sidereal days. Therefore, there is one fewer <a href="/wiki/Solar_day" class="mw-redirect" title="Solar day">solar day</a> per year than there are sidereal days, similar to an observation of the <a href="/wiki/Coin_rotation_paradox" title="Coin rotation paradox">coin rotation paradox</a>.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> This makes a sidereal day approximately <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">365.24</span><span class="sr-only">/</span><span class="den">366.24</span></span>⁠</span> times the length of the 24-hour solar day. </p> <div class="mw-heading mw-heading2"><h2 id="Effects_of_precession">Effects of precession</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Sidereal_time&action=edit&section=2" title="Edit section: Effects of precession"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Earth's rotation is not a simple rotation around an axis that remains always parallel to itself. Earth's rotational axis itself rotates about a second axis, <a href="/wiki/Orthogonality" title="Orthogonality">orthogonal</a> to the plane of Earth's orbit, taking about 25,800 years to perform a complete rotation. This phenomenon is termed the <a href="/wiki/Axial_precession" title="Axial precession">precession of the equinoxes</a>. Because of this precession, the stars appear to move around Earth in a manner more complicated than a simple constant rotation. </p><p>For this reason, to simplify the description of Earth's orientation in astronomy and <a href="/wiki/Geodesy" title="Geodesy">geodesy</a>, it was conventional to chart the positions of the stars in the sky according to <a href="/wiki/Right_ascension" title="Right ascension">right ascension</a> and <a href="/wiki/Declination" title="Declination">declination</a>, which are based on a frame of reference that follows Earth's precession, and to keep track of Earth's rotation, through sidereal time, relative to this frame as well. (The conventional reference frame, for purposes of star catalogues, was replaced in 1998 with the <a href="/wiki/International_Celestial_Reference_Frame" class="mw-redirect" title="International Celestial Reference Frame">International Celestial Reference Frame</a>, which is fixed with respect to extra-galactic radio sources. Because of the great distances, these sources have no appreciable <a href="/wiki/Proper_motion" title="Proper motion">proper motion</a>.<sup id="cite_ref-FOOTNOTEUrbanSeidelmann2013105_6-0" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann2013105-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup>) In this frame of reference, Earth's rotation is close to constant, but the stars appear to rotate slowly with a period of about 25,800 years. It is also in this frame of reference that the <a href="/wiki/Tropical_year" title="Tropical year">tropical year</a> (or solar year), the year related to Earth's seasons, represents one orbit of Earth around the Sun. The precise definition of a sidereal day is the time taken for one rotation of Earth in this precessing frame of reference. </p> <div class="mw-heading mw-heading2"><h2 id="Modern_definitions">Modern definitions</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Sidereal_time&action=edit&section=3" title="Edit section: Modern definitions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>During the past, time was measured by observing stars with instruments such as <a href="/wiki/Zenith_telescope" title="Zenith telescope">photographic zenith tubes</a> and <a href="/wiki/Andr%C3%A9-Louis_Danjon" title="André-Louis Danjon">Danjon</a> astrolabes, and the passage of stars across defined lines would be timed with the observatory clock. Then, using the <a href="/wiki/Right_ascension" title="Right ascension">right ascension</a> of the stars from a star catalog, the time when the star should have passed through the meridian of the observatory was computed, and a correction to the time kept by the observatory clock was computed. Sidereal time was defined such that the March equinox would <a href="/wiki/Astronomical_transit" title="Astronomical transit">transit</a> the meridian of the observatory at 0 hours local sidereal time.<sup id="cite_ref-FOOTNOTEES11961Ch_3,_"Systems_of_Time_Measurement"_7-0" class="reference"><a href="#cite_note-FOOTNOTEES11961Ch_3,_"Systems_of_Time_Measurement"-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p><p>Beginning during the 1970s, the <a href="/wiki/Radio_astronomy" title="Radio astronomy">radio astronomy</a> methods <a href="/wiki/Very-long-baseline_interferometry" title="Very-long-baseline interferometry">very-long-baseline interferometry</a> (VLBI) and <a href="/wiki/Pulsar_timing_array" title="Pulsar timing array">pulsar timing</a> overtook optical instruments for the most precise <a href="/wiki/Astrometry" title="Astrometry">astrometry</a>. This resulted in the determination of <a href="/wiki/UT1" class="mw-redirect" title="UT1">UT1</a> (mean solar time at 0° longitude) using VLBI, a new measure of the Earth Rotation Angle, and new definitions of sidereal time. These changes became effective 1 January 2003.<sup id="cite_ref-FOOTNOTEUrbanSeidelmann201378–81,_112_8-0" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann201378–81,_112-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Earth_rotation_angle">Earth rotation angle<span class="anchor" id="ERA"></span></h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Sidereal_time&action=edit&section=4" title="Edit section: Earth rotation angle"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <b>Earth rotation angle</b> (<b>ERA</b>) measures the rotation of the Earth from an origin on the celestial equator, the <i>Celestial Intermediate Origin</i>, also termed the <i>Celestial Ephemeris Origin</i>,<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> that has no instantaneous motion along the equator; it was originally referred to as the <i>non-rotating origin</i>. This point is very close to the equinox of J2000.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p><p>ERA, measured in <a href="/wiki/Radian" title="Radian">radians</a>, is related to <a href="/wiki/Universal_time" class="mw-redirect" title="Universal time">UT1</a> by a simple linear relation:<sup id="cite_ref-FOOTNOTEUrbanSeidelmann201378_3-1" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann201378-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> <span class="mwe-math-element"><span class="mwe-math-mathml-display mwe-math-mathml-a11y" style="display: none;"><math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \theta (t_{U})=2\pi (0.779\,057\,273\,2640+1.002\,737\,811\,911\,354\,48\cdot t_{U})}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>θ</mi> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>U</mi> </mrow> </msub> <mo stretchy="false">)</mo> <mo>=</mo> <mn>2</mn> <mi>π</mi> <mo stretchy="false">(</mo> <mn>0.779</mn> <mspace width="thinmathspace" /> <mn>057</mn> <mspace width="thinmathspace" /> <mn>273</mn> <mspace width="thinmathspace" /> <mn>2640</mn> <mo>+</mo> <mn>1.002</mn> <mspace width="thinmathspace" /> <mn>737</mn> <mspace width="thinmathspace" /> <mn>811</mn> <mspace width="thinmathspace" /> <mn>911</mn> <mspace width="thinmathspace" /> <mn>354</mn> <mspace width="thinmathspace" /> <mn>48</mn> <mo>⋅</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>U</mi> </mrow> </msub> <mo stretchy="false">)</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \theta (t_{U})=2\pi (0.779\,057\,273\,2640+1.002\,737\,811\,911\,354\,48\cdot t_{U})}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/b7311ab647d2eca6297dd81b28e378645e5ef90f" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:61.075ex; height:2.843ex;" alt="{\displaystyle \theta (t_{U})=2\pi (0.779\,057\,273\,2640+1.002\,737\,811\,911\,354\,48\cdot t_{U})}"></span> where <i>t<sub>U</sub></i> is the <a href="/wiki/Julian_day" title="Julian day">Julian UT1 date</a> (JD) minus 2451545.0. The linear coefficient represents the <a href="/wiki/Earth%27s_rotation_speed" class="mw-redirect" title="Earth's rotation speed">Earth's rotation speed</a> around its own axis. </p><p>ERA replaces <i>Greenwich Apparent Sidereal Time</i> (GAST). The origin on the celestial equator for GAST, termed the true <a href="/wiki/Equinox_(celestial_coordinates)" title="Equinox (celestial coordinates)">equinox</a>, does move, due to the movement of the equator and the ecliptic. The lack of motion of the origin of ERA is considered a significant advantage.<sup id="cite_ref-FOOTNOTEUrbanSeidelmann20136_11-0" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann20136-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p><p>The ERA may be converted to other units; for example, the <i>Astronomical Almanac for the Year 2017</i> tabulated it in degrees, minutes, and seconds.<sup id="cite_ref-FOOTNOTEAstronomical_Almanac2016B21–B24_12-0" class="reference"><a href="#cite_note-FOOTNOTEAstronomical_Almanac2016B21–B24-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p><p>As an example, the <i>Astronomical Almanac for the Year 2017</i> gave the ERA at 0 h 1 January 2017 UT1 as 100° 37′ 12.4365″.<sup id="cite_ref-FOOTNOTEAstronomical_Almanac2016B21_13-0" class="reference"><a href="#cite_note-FOOTNOTEAstronomical_Almanac2016B21-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> Since <a href="/wiki/Coordinated_Universal_Time" title="Coordinated Universal Time">Coordinated Universal Time</a> (UTC) is within a second or two of UT1, this can be used as an anchor to give the ERA approximately for a given civil time and date. </p> <div class="mw-heading mw-heading3"><h3 id="Mean_and_apparent_varieties">Mean and apparent varieties</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Sidereal_time&action=edit&section=5" title="Edit section: Mean and apparent varieties"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Sidereal_Clock_made_for_Sir_George_Augustus_William_Shuckburgh.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Sidereal_Clock_made_for_Sir_George_Augustus_William_Shuckburgh.jpg/220px-Sidereal_Clock_made_for_Sir_George_Augustus_William_Shuckburgh.jpg" decoding="async" width="220" height="431" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Sidereal_Clock_made_for_Sir_George_Augustus_William_Shuckburgh.jpg/330px-Sidereal_Clock_made_for_Sir_George_Augustus_William_Shuckburgh.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Sidereal_Clock_made_for_Sir_George_Augustus_William_Shuckburgh.jpg/440px-Sidereal_Clock_made_for_Sir_George_Augustus_William_Shuckburgh.jpg 2x" data-file-width="2500" data-file-height="4896" /></a><figcaption>One of the two known surviving sidereal angle clocks in the world, made by <a href="/wiki/John_Arnold_(watchmaker)" title="John Arnold (watchmaker)">John Arnold</a> & Son. It was previously owned by Sir <a href="/wiki/George_Shuckburgh-Evelyn" title="George Shuckburgh-Evelyn">George Shuckburgh-Evelyn</a>. It is on display in the <a href="/wiki/Royal_Observatory,_Greenwich" title="Royal Observatory, Greenwich">Royal Observatory, Greenwich</a>, London.</figcaption></figure> <p>Although ERA is intended to replace sidereal time, there is a need to maintain definitions for sidereal time during the transition, and when working with older data and documents. </p><p>Similarly to mean solar time, every location on Earth has its own local sidereal time (LST), depending on the longitude of the point. Since it is not feasible to publish tables for every longitude, astronomical tables use Greenwich sidereal time (GST), which is sidereal time on the <a href="/wiki/IERS_Reference_Meridian" title="IERS Reference Meridian">IERS Reference Meridian</a>, less precisely termed the Greenwich, or <a href="/wiki/Prime_meridian_(Greenwich)" title="Prime meridian (Greenwich)">Prime meridian</a>. There are two varieties, <b>mean sidereal time</b> if the mean equator and equinox of date are used, and <b>apparent sidereal time</b> if the apparent equator and equinox of date are used. The former ignores the effect of <a href="/wiki/Astronomical_nutation" title="Astronomical nutation">astronomical nutation</a> while the latter includes it. When the choice of location is combined with the choice of including astronomical nutation or not, the acronyms GMST, LMST, GAST, and LAST result. </p><p>The following relationships are true:<sup id="cite_ref-FOOTNOTEUrbanSeidelmann201380_14-0" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann201380-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p> <style data-mw-deduplicate="TemplateStyles:r996643573">.mw-parser-output .block-indent{padding-left:3em;padding-right:0;overflow:hidden}</style><div class="block-indent">local mean sidereal time = GMST + east longitude</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r996643573"><div class="block-indent">local apparent sidereal time = GAST + east longitude</div> <p>The new definitions of Greenwich mean and apparent sidereal time (since 2003, see above) are: <span class="mwe-math-element"><span class="mwe-math-mathml-display mwe-math-mathml-a11y" style="display: none;"><math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {GMST} (t_{U},t)=\theta (t_{U})-E_{\mathrm {PREC} }(t)}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">G</mi> <mi mathvariant="normal">M</mi> <mi mathvariant="normal">S</mi> <mi mathvariant="normal">T</mi> </mrow> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>U</mi> </mrow> </msub> <mo>,</mo> <mi>t</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mi>θ</mi> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>U</mi> </mrow> </msub> <mo stretchy="false">)</mo> <mo>−</mo> <msub> <mi>E</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">P</mi> <mi mathvariant="normal">R</mi> <mi mathvariant="normal">E</mi> <mi mathvariant="normal">C</mi> </mrow> </mrow> </msub> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathrm {GMST} (t_{U},t)=\theta (t_{U})-E_{\mathrm {PREC} }(t)}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/fb90ed050b95238dd223ccec27525a6605595186" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:33.343ex; height:2.843ex;" alt="{\displaystyle \mathrm {GMST} (t_{U},t)=\theta (t_{U})-E_{\mathrm {PREC} }(t)}"></span> <span class="mwe-math-element"><span class="mwe-math-mathml-display mwe-math-mathml-a11y" style="display: none;"><math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {GAST} (t_{U},t)=\theta (t_{U})-E_{0}(t)}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">G</mi> <mi mathvariant="normal">A</mi> <mi mathvariant="normal">S</mi> <mi mathvariant="normal">T</mi> </mrow> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>U</mi> </mrow> </msub> <mo>,</mo> <mi>t</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mi>θ</mi> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>U</mi> </mrow> </msub> <mo stretchy="false">)</mo> <mo>−</mo> <msub> <mi>E</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathrm {GAST} (t_{U},t)=\theta (t_{U})-E_{0}(t)}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/3c5978bbd6a96c478acc810b901faa0155d078aa" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:29.143ex; height:2.843ex;" alt="{\displaystyle \mathrm {GAST} (t_{U},t)=\theta (t_{U})-E_{0}(t)}"></span> </p><p>such that <i>θ</i> is the Earth Rotation Angle, <i>E</i><sub>PREC</sub> is the accumulated precession, and <i>E</i><sub>0</sub> is equation of the origins, which represents accumulated precession and nutation.<sup id="cite_ref-FOOTNOTEUrbanSeidelmann201378–79_15-0" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann201378–79-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> The calculation of precession and nutation was described in Chapter 6 of Urban & Seidelmann. </p><p>As an example, the <i>Astronomical Almanac for the Year 2017</i> gave the ERA at 0 h 1 January 2017 UT1 as 100° 37′ 12.4365″. The GAST was 6 h 43 m 20.7109 s. For GMST the hour and minute were the same but the second was 21.1060.<sup id="cite_ref-FOOTNOTEAstronomical_Almanac2016B21_13-1" class="reference"><a href="#cite_note-FOOTNOTEAstronomical_Almanac2016B21-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Relationship_between_solar_time_and_sidereal_time_intervals">Relationship between solar time and sidereal time intervals</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Sidereal_time&action=edit&section=6" title="Edit section: Relationship between solar time and sidereal time intervals"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:ConantClock.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a5/ConantClock.png/170px-ConantClock.png" decoding="async" width="170" height="229" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a5/ConantClock.png/255px-ConantClock.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a5/ConantClock.png/340px-ConantClock.png 2x" data-file-width="1435" data-file-height="1934" /></a><figcaption>This <a href="/wiki/Astronomical_clock" title="Astronomical clock">astronomical clock</a> uses dials showing both sidereal and <a href="/wiki/Solar_time" title="Solar time">solar time</a>.</figcaption></figure> <p>If a certain interval <i>I</i> is measured in both mean solar time (UT1) and sidereal time, the numerical value will be greater in sidereal time than in UT1, because sidereal days are shorter than UT1 days. The ratio is: <span class="mwe-math-element"><span class="mwe-math-mathml-display mwe-math-mathml-a11y" style="display: none;"><math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {I_{\mathrm {mean\,sidereal} }}{I_{\mathrm {UT1} }}}=r'=1.002\,737\,379\,093\,507\,95+5.9006\times 10^{-11}t-5.9\times 10^{-15}t^{2}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>I</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">m</mi> <mi mathvariant="normal">e</mi> <mi mathvariant="normal">a</mi> <mi mathvariant="normal">n</mi> <mspace width="thinmathspace" /> <mi mathvariant="normal">s</mi> <mi mathvariant="normal">i</mi> <mi mathvariant="normal">d</mi> <mi mathvariant="normal">e</mi> <mi mathvariant="normal">r</mi> <mi mathvariant="normal">e</mi> <mi mathvariant="normal">a</mi> <mi mathvariant="normal">l</mi> </mrow> </mrow> </msub> <msub> <mi>I</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">U</mi> <mi mathvariant="normal">T</mi> <mn>1</mn> </mrow> </mrow> </msub> </mfrac> </mrow> <mo>=</mo> <msup> <mi>r</mi> <mo>′</mo> </msup> <mo>=</mo> <mn>1.002</mn> <mspace width="thinmathspace" /> <mn>737</mn> <mspace width="thinmathspace" /> <mn>379</mn> <mspace width="thinmathspace" /> <mn>093</mn> <mspace width="thinmathspace" /> <mn>507</mn> <mspace width="thinmathspace" /> <mn>95</mn> <mo>+</mo> <mn>5.9006</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>11</mn> </mrow> </msup> <mi>t</mi> <mo>−</mo> <mn>5.9</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>15</mn> </mrow> </msup> <msup> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {I_{\mathrm {mean\,sidereal} }}{I_{\mathrm {UT1} }}}=r'=1.002\,737\,379\,093\,507\,95+5.9006\times 10^{-11}t-5.9\times 10^{-15}t^{2}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4cf351668faedeb6ea445d0a4b4dcdc85fd93cc2" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.338ex; width:77.639ex; height:5.676ex;" alt="{\displaystyle {\frac {I_{\mathrm {mean\,sidereal} }}{I_{\mathrm {UT1} }}}=r'=1.002\,737\,379\,093\,507\,95+5.9006\times 10^{-11}t-5.9\times 10^{-15}t^{2}}"></span> </p><p>such that <i>t</i> represents the number of Julian centuries elapsed since noon 1 January 2000 <a href="/wiki/Terrestrial_Time" title="Terrestrial Time">Terrestrial Time</a>.<sup id="cite_ref-FOOTNOTEUrbanSeidelmann201381_16-0" class="reference"><a href="#cite_note-FOOTNOTEUrbanSeidelmann201381-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Sidereal_days_compared_to_solar_days_on_other_planets">Sidereal days compared to solar days on other planets</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Sidereal_time&action=edit&section=7" title="Edit section: Sidereal days compared to solar days on other planets"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Six of the eight solar <a href="/wiki/Planet" title="Planet">planets</a> have <a href="/wiki/Retrograde_and_prograde_motion" title="Retrograde and prograde motion">prograde</a> rotation—that is, they rotate more than once per year in the same direction as they orbit the Sun, so the Sun rises in the east.<sup id="cite_ref-FOOTNOTEBakich2000_17-0" class="reference"><a href="#cite_note-FOOTNOTEBakich2000-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Venus" title="Venus">Venus</a> and <a href="/wiki/Uranus" title="Uranus">Uranus</a>, however, have <a href="/wiki/Retrograde_motion" class="mw-redirect" title="Retrograde motion">retrograde</a> rotation. For prograde rotation, the formula relating the lengths of the sidereal and solar days is: </p> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r996643573"><div class="block-indent">number of sidereal days per orbital period = 1 + number of solar days per orbital period</div> <p>or, equivalently: </p> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r996643573"><div class="block-indent">length of solar day = <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num">length of sidereal day</span><span class="sr-only">/</span><span class="den">1 − <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num">length of sidereal day</span><span class="sr-only">/</span><span class="den">orbital period</span></span>⁠</span></span></span>⁠</span>.</div> <p>When calculating the formula for a retrograde rotation, the operator of the denominator will be a plus sign (put another way, in the original formula the length of the sidereal day must be treated as negative). This is due to the solar day being shorter than the sidereal day for retrograde rotation, as the rotation of the planet would be against the direction of orbital motion. </p><p>If a planet rotates prograde, and the sidereal day exactly equals the orbital period, then the formula above gives an infinitely long solar day (<a href="/wiki/Division_by_zero" title="Division by zero">division by zero</a>). This is the case for a planet in <a href="/wiki/Tidal_locking" title="Tidal locking">synchronous rotation</a>; in the case of zero eccentricity, one hemisphere experiences eternal day, the other eternal night, with a "twilight belt" separating them. </p><p>All the solar planets more distant from the Sun than Earth are similar to Earth in that, since they experience many rotations per revolution around the Sun, there is only a small difference between the length of the sidereal day and that of the solar day – the ratio of the former to the latter never being less than Earth's ratio of 0.997. But the situation is quite different for <a href="/wiki/Mercury_(planet)" title="Mercury (planet)">Mercury</a> and Venus. Mercury's sidereal day is about two-thirds of its orbital period, so by the prograde formula its solar day lasts for two revolutions around the Sun – three times as long as its sidereal day. Venus rotates retrograde with a sidereal day lasting about 243.0 Earth days, or about 1.08 times its orbital period of 224.7 Earth days; hence by the retrograde formula its solar day is about 116.8 Earth days, and it has about 1.9 solar days per orbital period. </p><p>By convention, rotation periods of planets are given in sidereal terms unless otherwise specified. </p> <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=Sidereal_time&action=edit&section=8" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Anti-sidereal_time" title="Anti-sidereal time">Anti-sidereal time</a></li> <li><a href="/wiki/Earth%27s_rotation" title="Earth's rotation">Earth's rotation</a></li> <li><a href="/wiki/International_Celestial_Reference_Frame" class="mw-redirect" title="International Celestial Reference Frame">International Celestial Reference Frame</a></li> <li><a href="/wiki/Nocturnal_(instrument)" title="Nocturnal (instrument)">Nocturnal (instrument)</a></li> <li><a href="/wiki/Sidereal_month" class="mw-redirect" title="Sidereal month">Sidereal month</a></li> <li><a href="/wiki/Sidereal_year" title="Sidereal year">Sidereal year</a></li> <li><a href="/wiki/Synodic_day" title="Synodic day">Synodic day</a></li> <li><a href="/wiki/Transit_instrument" title="Transit instrument">Transit instrument</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="Citations">Citations</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Sidereal_time&action=edit&section=9" title="Edit section: Citations"><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 mw-references-columns"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><a href="#CITEREFNISTn.d.">NIST n.d.</a> A more precise definition is given below.</span> </li> <li id="cite_note-FOOTNOTEUrbanSeidelmann2013"Glossary"_s.v._hour_angle,_hour_circle,_sidereal_time-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEUrbanSeidelmann2013"Glossary"_s.v._hour_angle,_hour_circle,_sidereal_time_2-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFUrbanSeidelmann2013">Urban & Seidelmann 2013</a>, "Glossary" s.v. hour angle, hour circle, sidereal time.</span> </li> <li id="cite_note-FOOTNOTEUrbanSeidelmann201378-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEUrbanSeidelmann201378_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEUrbanSeidelmann201378_3-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFUrbanSeidelmann2013">Urban & Seidelmann 2013</a>, p. 78.</span> </li> <li id="cite_note-FOOTNOTEIERS2013-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEIERS2013_4-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFIERS2013">IERS 2013</a>.</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"><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 id="CITEREFBartlett1904" class="citation journal cs1">Bartlett, A. K. (1904). <a rel="nofollow" class="external text" href="http://adsabs.harvard.edu/full/1904PA.....12..649B">"Solar and Sidereal Time"</a>. <i><a href="/wiki/Popular_Astronomy_(US_magazine)" title="Popular Astronomy (US magazine)">Popular Astronomy</a></i>. <b>12</b>: 649–651. <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/1904PA.....12..649B">1904PA.....12..649B</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Popular+Astronomy&rft.atitle=Solar+and+Sidereal+Time&rft.volume=12&rft.pages=649-651&rft.date=1904&rft_id=info%3Abibcode%2F1904PA.....12..649B&rft.aulast=Bartlett&rft.aufirst=A.+K.&rft_id=http%3A%2F%2Fadsabs.harvard.edu%2Ffull%2F1904PA.....12..649B&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" class="Z3988"></span></span> </li> <li id="cite_note-FOOTNOTEUrbanSeidelmann2013105-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEUrbanSeidelmann2013105_6-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFUrbanSeidelmann2013">Urban & Seidelmann 2013</a>, p. 105.</span> </li> <li id="cite_note-FOOTNOTEES11961Ch_3,_"Systems_of_Time_Measurement"-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEES11961Ch_3,_"Systems_of_Time_Measurement"_7-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFES11961">ES1 1961</a>, Ch 3, "Systems of Time Measurement".</span> </li> <li id="cite_note-FOOTNOTEUrbanSeidelmann201378–81,_112-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEUrbanSeidelmann201378–81,_112_8-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFUrbanSeidelmann2013">Urban & Seidelmann 2013</a>, pp. 78–81, 112.</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"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation encyclopaedia cs1"><a rel="nofollow" class="external text" href="https://www.iers.org/IERS/EN/Service/Glossary/celestialIntermediateOrigin.html?nn=14894">"Celestial Intermediate Origin (CIO)"</a>. <i>Glossary of the <a href="/wiki/IERS" class="mw-redirect" title="IERS">IERS</a> Conventions (2010)</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Celestial+Intermediate+Origin+%28CIO%29&rft.btitle=Glossary+of+the+IERS+Conventions+%282010%29&rft_id=https%3A%2F%2Fwww.iers.org%2FIERS%2FEN%2FService%2FGlossary%2FcelestialIntermediateOrigin.html%3Fnn%3D14894&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" 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 class="citation encyclopaedia cs1"><a rel="nofollow" class="external text" href="https://www.iers.org/IERS/EN/Service/Glossary/ceo.html?nn=14894">"Celestial Ephemeris Origin"</a>. <i>Glossary of the <a href="/wiki/IERS" class="mw-redirect" title="IERS">IERS</a> Conventions (2010)</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Celestial+Ephemeris+Origin&rft.btitle=Glossary+of+the+IERS+Conventions+%282010%29&rft_id=https%3A%2F%2Fwww.iers.org%2FIERS%2FEN%2FService%2FGlossary%2Fceo.html%3Fnn%3D14894&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" class="Z3988"></span></span> </li> <li id="cite_note-FOOTNOTEUrbanSeidelmann20136-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEUrbanSeidelmann20136_11-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFUrbanSeidelmann2013">Urban & Seidelmann 2013</a>, p. 6.</span> </li> <li id="cite_note-FOOTNOTEAstronomical_Almanac2016B21–B24-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEAstronomical_Almanac2016B21–B24_12-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFAstronomical_Almanac2016">Astronomical Almanac 2016</a>, pp. B21–B24.</span> </li> <li id="cite_note-FOOTNOTEAstronomical_Almanac2016B21-13"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEAstronomical_Almanac2016B21_13-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEAstronomical_Almanac2016B21_13-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFAstronomical_Almanac2016">Astronomical Almanac 2016</a>, p. B21.</span> </li> <li id="cite_note-FOOTNOTEUrbanSeidelmann201380-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEUrbanSeidelmann201380_14-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFUrbanSeidelmann2013">Urban & Seidelmann 2013</a>, p. 80.</span> </li> <li id="cite_note-FOOTNOTEUrbanSeidelmann201378–79-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEUrbanSeidelmann201378–79_15-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFUrbanSeidelmann2013">Urban & Seidelmann 2013</a>, pp. 78–79.</span> </li> <li id="cite_note-FOOTNOTEUrbanSeidelmann201381-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEUrbanSeidelmann201381_16-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFUrbanSeidelmann2013">Urban & Seidelmann 2013</a>, p. 81.</span> </li> <li id="cite_note-FOOTNOTEBakich2000-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEBakich2000_17-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFBakich2000">Bakich 2000</a>.</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=Sidereal_time&action=edit&section=10" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAstronomical_Almanac2016" class="citation book cs1"><i>Astronomical Almanac for the Year 2017</i>. Washington and Taunton: US Government Printing Office and The UK Hydrographic Office. 2016. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-7077-41666" title="Special:BookSources/978-0-7077-41666"><bdi>978-0-7077-41666</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Astronomical+Almanac+for+the+Year+2017&rft.place=Washington+and+Taunton&rft.pub=US+Government+Printing+Office+and+The+UK+Hydrographic+Office&rft.date=2016&rft.isbn=978-0-7077-41666&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBakich2000" class="citation book cs1">Bakich, Michael E. (2000). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/cambridgeplaneta00baki"><i>The Cambridge Planetary Handbook</i></a></span>. Cambridge University Press. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-521-63280-3" title="Special:BookSources/0-521-63280-3"><bdi>0-521-63280-3</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+Cambridge+Planetary+Handbook&rft.pub=Cambridge+University+Press&rft.date=2000&rft.isbn=0-521-63280-3&rft.aulast=Bakich&rft.aufirst=Michael+E.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fcambridgeplaneta00baki&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFIERS2013" class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.iers.org/IERS/EN/Service/Glossary/era.html?nn=14894">"Earth Rotation Angle"</a>. <i>International Earth Rotation and Reference System Service</i>. 2013<span class="reference-accessdate">. Retrieved <span class="nowrap">20 March</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=International+Earth+Rotation+and+Reference+System+Service&rft.atitle=Earth+Rotation+Angle&rft.date=2013&rft_id=https%3A%2F%2Fwww.iers.org%2FIERS%2FEN%2FService%2FGlossary%2Fera.html%3Fnn%3D14894&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFES11961" class="citation book cs1"><i>Explanatory Supplement to the Ephemeris</i>. London: Her Majesty's Stationery Office. 1961.</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+Ephemeris&rft.place=London&rft.pub=Her+Majesty%27s+Stationery+Office&rft.date=1961&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFNISTn.d." class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/time-frequency-z/time-and-frequency-z-s-so">"Time and Frequency from A to Z, S to So"</a>. <i><a href="/wiki/National_Institute_of_Standards_and_Technology" title="National Institute of Standards and Technology">National Institute of Standards and Technology</a></i>. 12 May 2010.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=National+Institute+of+Standards+and+Technology&rft.atitle=Time+and+Frequency+from+A+to+Z%2C+S+to+So&rft.date=2010-05-12&rft_id=https%3A%2F%2Fwww.nist.gov%2Fpml%2Ftime-and-frequency-division%2Fpopular-links%2Ftime-frequency-z%2Ftime-and-frequency-z-s-so&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFUrbanSeidelmann2013" class="citation book cs1">Urban, Sean E.; Seidelmann, P. Kenneth, eds. (2013). <i>Explanatory Supplement to the Astronomical Almanac</i> (3rd ed.). Mill Valley, CA: University Science Books. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-891389-85-6" title="Special:BookSources/978-1-891389-85-6"><bdi>978-1-891389-85-6</bdi></a>.</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+Almanac&rft.place=Mill+Valley%2C+CA&rft.edition=3rd&rft.pub=University+Science+Books&rft.date=2013&rft.isbn=978-1-891389-85-6&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASidereal+time" class="Z3988"></span></li></ul> <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=Sidereal_time&action=edit&section=11" 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/Special:Search/sidereal_time" class="extiw" title="wiktionary:Special:Search/sidereal time">sidereal time</a></b></i> in Wiktionary, the free dictionary.</div></div> </div> <ul><li><a rel="nofollow" class="external text" href="https://aa.usno.navy.mil/data/siderealtime">Web-based Sidereal time calculator</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 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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 class="mw-selflink selflink">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 class="mw-selflink selflink">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 href="/wiki/Second" title="Second">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> <style data-mw-deduplicate="TemplateStyles:r1130092004">.mw-parser-output .portal-bar{font-size:88%;font-weight:bold;display:flex;justify-content:center;align-items:baseline}.mw-parser-output .portal-bar-bordered{padding:0 2em;background-color:#fdfdfd;border:1px solid #a2a9b1;clear:both;margin:1em auto 0}.mw-parser-output .portal-bar-related{font-size:100%;justify-content:flex-start}.mw-parser-output .portal-bar-unbordered{padding:0 1.7em;margin-left:0}.mw-parser-output .portal-bar-header{margin:0 1em 0 0.5em;flex:0 0 auto;min-height:24px}.mw-parser-output .portal-bar-content{display:flex;flex-flow:row 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