CINXE.COM

<!DOCTYPE html> <html dir="ltr" lang="en-US" prefix="og: https://ogp.me/ns#"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <link rel="profile" href="https://gmpg.org/xfn/11"> <title>Wavelength and Magnitude Conversions - SDSS</title>  <meta name="description" content="This page gives information about how to convert between the wavelength and magnitude conventions used by the SDSS and other systems. Conversion between vacuum and air wavelengths The SDSS data describing spectral line wavelengths use vacuum wavelengths. However, the wavelengths of atomic transitions are usually quoted at standard temperature and pressure (S.T.P.); this is how" /> <meta name="robots" content="max-image-preview:large" /> <link rel="canonical" href="https://www.sdss.org/dr18/tutorials/conversions/" /> <meta name="generator" content="All in One SEO (AIOSEO) 4.6.7.1" /> <meta property="og:locale" content="en_US" /> <meta property="og:site_name" content="SDSS - Mapping the Universe" /> <meta property="og:type" content="article" /> <meta property="og:title" content="Wavelength and Magnitude Conversions - SDSS" /> <meta property="og:description" content="This page gives information about how to convert between the wavelength and magnitude conventions used by the SDSS and other systems. Conversion between vacuum and air wavelengths The SDSS data describing spectral line wavelengths use vacuum wavelengths. However, the wavelengths of atomic transitions are usually quoted at standard temperature and pressure (S.T.P.); this is how" /> <meta property="og:url" content="https://www.sdss.org/dr18/tutorials/conversions/" /> <meta property="og:image" content="https://www.sdss.org/wp-content/uploads/2022/09/sdss-new-logo-72dpi.png" /> <meta property="og:image:secure_url" content="https://www.sdss.org/wp-content/uploads/2022/09/sdss-new-logo-72dpi.png" /> <meta property="article:published_time" content="2023-05-24T15:39:28+00:00" /> <meta property="article:modified_time" content="2023-07-26T15:38:37+00:00" /> <meta name="twitter:card" content="summary_large_image" /> <meta name="twitter:title" content="Wavelength and Magnitude Conversions - SDSS" /> <meta name="twitter:description" content="This page gives information about how to convert between the wavelength and magnitude conventions used by the SDSS and other systems. Conversion between vacuum and air wavelengths The SDSS data describing spectral line wavelengths use vacuum wavelengths. However, the wavelengths of atomic transitions are usually quoted at standard temperature and pressure (S.T.P.); this is how" /> <meta name="twitter:image" content="https://www.sdss.org/wp-content/uploads/2022/09/sdss-new-logo-72dpi.png" /> <script type="application/ld+json" class="aioseo-schema"> {"@context":"https:\/\/schema.org","@graph":[{"@type":"BreadcrumbList","@id":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/#breadcrumblist","itemListElement":[{"@type":"ListItem","@id":"https:\/\/www.sdss.org\/#listItem","position":1,"name":"Home","item":"https:\/\/www.sdss.org\/","nextItem":"https:\/\/www.sdss.org\/dr18\/#listItem"},{"@type":"ListItem","@id":"https:\/\/www.sdss.org\/dr18\/#listItem","position":2,"name":"Data Release 18","item":"https:\/\/www.sdss.org\/dr18\/","nextItem":"https:\/\/www.sdss.org\/dr18\/tutorials\/#listItem","previousItem":"https:\/\/www.sdss.org\/#listItem"},{"@type":"ListItem","@id":"https:\/\/www.sdss.org\/dr18\/tutorials\/#listItem","position":3,"name":"Tutorials Overview","item":"https:\/\/www.sdss.org\/dr18\/tutorials\/","nextItem":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/#listItem","previousItem":"https:\/\/www.sdss.org\/dr18\/#listItem"},{"@type":"ListItem","@id":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/#listItem","position":4,"name":"Wavelength and Magnitude Conversions","previousItem":"https:\/\/www.sdss.org\/dr18\/tutorials\/#listItem"}]},{"@type":"Organization","@id":"https:\/\/www.sdss.org\/#organization","name":"SDSS","description":"Mapping the Universe","url":"https:\/\/www.sdss.org\/","logo":{"@type":"ImageObject","url":"\/wp-content\/uploads\/2022\/09\/sdss-new-logo-72dpi.png","@id":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/#organizationLogo"},"image":{"@id":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/#organizationLogo"},"sameAs":["https:\/\/en.wikipedia.org\/wiki\/Sloan_Digital_Sky_Survey"]},{"@type":"WebPage","@id":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/#webpage","url":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/","name":"Wavelength and Magnitude Conversions - SDSS","description":"This page gives information about how to convert between the wavelength and magnitude conventions used by the SDSS and other systems. Conversion between vacuum and air wavelengths The SDSS data describing spectral line wavelengths use vacuum wavelengths. However, the wavelengths of atomic transitions are usually quoted at standard temperature and pressure (S.T.P.); this is how","inLanguage":"en-US","isPartOf":{"@id":"https:\/\/www.sdss.org\/#website"},"breadcrumb":{"@id":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/#breadcrumblist"},"datePublished":"2023-05-24T15:39:28+00:00","dateModified":"2023-07-26T15:38:37+00:00"},{"@type":"WebSite","@id":"https:\/\/www.sdss.org\/#website","url":"https:\/\/www.sdss.org\/","name":"SDSS","description":"Mapping the Universe","inLanguage":"en-US","publisher":{"@id":"https:\/\/www.sdss.org\/#organization"}}]} </script>  <link rel='dns-prefetch' href='//www.sdss.org' /> <link rel="alternate" type="application/rss+xml" title="SDSS » Feed" href="https://www.sdss.org/feed/" /> <link rel="alternate" type="application/rss+xml" title="SDSS » Comments Feed" href="https://www.sdss.org/comments/feed/" />  <script src="//www.googletagmanager.com/gtag/js?id=G-5BJ0FDW1X0" data-cfasync="false" data-wpfc-render="false" async></script> <script data-cfasync="false" data-wpfc-render="false"> var mi_version = '8.28.0'; var mi_track_user = true; var mi_no_track_reason = ''; var MonsterInsightsDefaultLocations = {"page_location":"https:\/\/www.sdss.org\/dr18\/tutorials\/conversions\/"}; if ( typeof MonsterInsightsPrivacyGuardFilter === 'function' ) { var MonsterInsightsLocations = (typeof MonsterInsightsExcludeQuery === 'object') ? MonsterInsightsPrivacyGuardFilter( MonsterInsightsExcludeQuery ) : MonsterInsightsPrivacyGuardFilter( MonsterInsightsDefaultLocations ); } else { var MonsterInsightsLocations = (typeof MonsterInsightsExcludeQuery === 'object') ? MonsterInsightsExcludeQuery : MonsterInsightsDefaultLocations; } var disableStrs = [ 'ga-disable-G-5BJ0FDW1X0', ]; /* Function to detect opted out users */ function __gtagTrackerIsOptedOut() { for (var index = 0; index < disableStrs.length; index++) { if (document.cookie.indexOf(disableStrs[index] + '=true') > -1) { return true; } } return false; } /* Disable tracking if the opt-out cookie exists. */ if (__gtagTrackerIsOptedOut()) { for (var index = 0; index < disableStrs.length; index++) { window[disableStrs[index]] = true; } } /* Opt-out function */ function __gtagTrackerOptout() { for (var index = 0; index < disableStrs.length; index++) { document.cookie = disableStrs[index] + '=true; expires=Thu, 31 Dec 2099 23:59:59 UTC; path=/'; window[disableStrs[index]] = true; } } if ('undefined' === typeof gaOptout) { function gaOptout() { __gtagTrackerOptout(); } } window.dataLayer = window.dataLayer || []; window.MonsterInsightsDualTracker = { helpers: {}, trackers: {}, }; if (mi_track_user) { function __gtagDataLayer() { dataLayer.push(arguments); } function __gtagTracker(type, name, parameters) { if (!parameters) { parameters = {}; } if (parameters.send_to) { __gtagDataLayer.apply(null, arguments); return; } if (type === 'event') { parameters.send_to = monsterinsights_frontend.v4_id; var hookName = name; if (typeof parameters['event_category'] !== 'undefined') { hookName = parameters['event_category'] + ':' + name; } if (typeof MonsterInsightsDualTracker.trackers[hookName] !== 'undefined') { MonsterInsightsDualTracker.trackers[hookName](parameters); } else { __gtagDataLayer('event', name, parameters); } } else { __gtagDataLayer.apply(null, arguments); } } __gtagTracker('js', new Date()); __gtagTracker('set', { 'developer_id.dZGIzZG': true, }); if ( MonsterInsightsLocations.page_location ) { __gtagTracker('set', MonsterInsightsLocations); } __gtagTracker('config', 'G-5BJ0FDW1X0', {"forceSSL":"true","link_attribution":"true"} ); window.gtag = __gtagTracker; (function () { /* https://developers.google.com/analytics/devguides/collection/analyticsjs/ */ /* ga and __gaTracker compatibility shim. */ var noopfn = function () { return null; }; var newtracker = function () { return new Tracker(); }; var Tracker = function () { return null; }; var p = Tracker.prototype; p.get = noopfn; p.set = noopfn; p.send = function () { var args = Array.prototype.slice.call(arguments); args.unshift('send'); __gaTracker.apply(null, args); }; var __gaTracker = function () { var len = arguments.length; if (len === 0) { return; } var f = arguments[len - 1]; if (typeof f !== 'object' || f === null || typeof f.hitCallback !== 'function') { if ('send' === arguments[0]) { var hitConverted, hitObject = false, action; if ('event' === arguments[1]) { if ('undefined' !== typeof arguments[3]) { hitObject = { 'eventAction': arguments[3], 'eventCategory': arguments[2], 'eventLabel': arguments[4], 'value': arguments[5] ? arguments[5] : 1, } } } if ('pageview' === arguments[1]) { if ('undefined' !== typeof arguments[2]) { hitObject = { 'eventAction': 'page_view', 'page_path': arguments[2], } } } if (typeof arguments[2] === 'object') { hitObject = arguments[2]; } if (typeof arguments[5] === 'object') { Object.assign(hitObject, arguments[5]); } if ('undefined' !== typeof arguments[1].hitType) { hitObject = arguments[1]; if ('pageview' === hitObject.hitType) { hitObject.eventAction = 'page_view'; } } if (hitObject) { action = 'timing' === arguments[1].hitType ? 'timing_complete' : hitObject.eventAction; hitConverted = mapArgs(hitObject); __gtagTracker('event', action, hitConverted); } } return; } function mapArgs(args) { var arg, hit = {}; var gaMap = { 'eventCategory': 'event_category', 'eventAction': 'event_action', 'eventLabel': 'event_label', 'eventValue': 'event_value', 'nonInteraction': 'non_interaction', 'timingCategory': 'event_category', 'timingVar': 'name', 'timingValue': 'value', 'timingLabel': 'event_label', 'page': 'page_path', 'location': 'page_location', 'title': 'page_title', 'referrer' : 'page_referrer', }; for (arg in args) { if (!(!args.hasOwnProperty(arg) || !gaMap.hasOwnProperty(arg))) { hit[gaMap[arg]] = args[arg]; } else { hit[arg] = args[arg]; } } return hit; } try { f.hitCallback(); } catch (ex) { } }; __gaTracker.create = newtracker; __gaTracker.getByName = newtracker; __gaTracker.getAll = function () { return []; }; __gaTracker.remove = noopfn; __gaTracker.loaded = true; window['__gaTracker'] = __gaTracker; })(); } else { console.log(""); (function () { function __gtagTracker() { return null; } window['__gtagTracker'] = __gtagTracker; window['gtag'] = __gtagTracker; })(); } </script>  <script> window._wpemojiSettings = {"baseUrl":"https:\/\/s.w.org\/images\/core\/emoji\/15.0.3\/72x72\/","ext":".png","svgUrl":"https:\/\/s.w.org\/images\/core\/emoji\/15.0.3\/svg\/","svgExt":".svg","source":{"concatemoji":"https:\/\/www.sdss.org\/wp-includes\/js\/wp-emoji-release.min.js?ver=6.6"}}; /*! This file is auto-generated */ !function(i,n){var o,s,e;function c(e){try{var t={supportTests:e,timestamp:(new Date).valueOf()};sessionStorage.setItem(o,JSON.stringify(t))}catch(e){}}function p(e,t,n){e.clearRect(0,0,e.canvas.width,e.canvas.height),e.fillText(t,0,0);var t=new Uint32Array(e.getImageData(0,0,e.canvas.width,e.canvas.height).data),r=(e.clearRect(0,0,e.canvas.width,e.canvas.height),e.fillText(n,0,0),new Uint32Array(e.getImageData(0,0,e.canvas.width,e.canvas.height).data));return t.every(function(e,t){return e===r[t]})}function u(e,t,n){switch(t){case"flag":return n(e,"\ud83c\udff3\ufe0f\u200d\u26a7\ufe0f","\ud83c\udff3\ufe0f\u200b\u26a7\ufe0f")?!1:!n(e,"\ud83c\uddfa\ud83c\uddf3","\ud83c\uddfa\u200b\ud83c\uddf3")&&!n(e,"\ud83c\udff4\udb40\udc67\udb40\udc62\udb40\udc65\udb40\udc6e\udb40\udc67\udb40\udc7f","\ud83c\udff4\u200b\udb40\udc67\u200b\udb40\udc62\u200b\udb40\udc65\u200b\udb40\udc6e\u200b\udb40\udc67\u200b\udb40\udc7f");case"emoji":return!n(e,"\ud83d\udc26\u200d\u2b1b","\ud83d\udc26\u200b\u2b1b")}return!1}function f(e,t,n){var r="undefined"!=typeof WorkerGlobalScope&&self instanceof WorkerGlobalScope?new OffscreenCanvas(300,150):i.createElement("canvas"),a=r.getContext("2d",{willReadFrequently:!0}),o=(a.textBaseline="top",a.font="600 32px Arial",{});return e.forEach(function(e){o[e]=t(a,e,n)}),o}function t(e){var t=i.createElement("script");t.src=e,t.defer=!0,i.head.appendChild(t)}"undefined"!=typeof Promise&&(o="wpEmojiSettingsSupports",s=["flag","emoji"],n.supports={everything:!0,everythingExceptFlag:!0},e=new Promise(function(e){i.addEventListener("DOMContentLoaded",e,{once:!0})}),new Promise(function(t){var n=function(){try{var e=JSON.parse(sessionStorage.getItem(o));if("object"==typeof e&&"number"==typeof e.timestamp&&(new Date).valueOf()<e.timestamp+604800&&"object"==typeof e.supportTests)return e.supportTests}catch(e){}return null}();if(!n){if("undefined"!=typeof Worker&&"undefined"!=typeof OffscreenCanvas&&"undefined"!=typeof URL&&URL.createObjectURL&&"undefined"!=typeof Blob)try{var e="postMessage("+f.toString()+"("+[JSON.stringify(s),u.toString(),p.toString()].join(",")+"));",r=new Blob([e],{type:"text/javascript"}),a=new Worker(URL.createObjectURL(r),{name:"wpTestEmojiSupports"});return void(a.onmessage=function(e){c(n=e.data),a.terminate(),t(n)})}catch(e){}c(n=f(s,u,p))}t(n)}).then(function(e){for(var t in e)n.supports[t]=e[t],n.supports.everything=n.supports.everything&&n.supports[t],"flag"!==t&&(n.supports.everythingExceptFlag=n.supports.everythingExceptFlag&&n.supports[t]);n.supports.everythingExceptFlag=n.supports.everythingExceptFlag&&!n.supports.flag,n.DOMReady=!1,n.readyCallback=function(){n.DOMReady=!0}}).then(function(){return e}).then(function(){var e;n.supports.everything||(n.readyCallback(),(e=n.source||{}).concatemoji?t(e.concatemoji):e.wpemoji&&e.twemoji&&(t(e.twemoji),t(e.wpemoji)))}))}((window,document),window._wpemojiSettings); </script> <link rel='stylesheet' id='wp-quicklatex-format-css' href='https://www.sdss.org/wp-content/plugins/wp-quicklatex/css/quicklatex-format.css?ver=6.6' media='all' /> <style id='wp-emoji-styles-inline-css'> img.wp-smiley, img.emoji { display: inline !important; border: none !important; box-shadow: none !important; height: 1em !important; width: 1em !important; margin: 0 0.07em !important; vertical-align: -0.1em !important; background: none !important; padding: 0 !important; } </style> <link rel='stylesheet' id='wp-block-library-css' href='https://www.sdss.org/wp-includes/css/dist/block-library/style.min.css?ver=6.6' media='all' /> <style id='pdfemb-pdf-embedder-viewer-style-inline-css'> .wp-block-pdfemb-pdf-embedder-viewer{max-width:none} </style> <style id='classic-theme-styles-inline-css'> /*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} </style> <style id='global-styles-inline-css'> :root{--wp--preset--aspect-ratio--square: 1;--wp--preset--aspect-ratio--4-3: 4/3;--wp--preset--aspect-ratio--3-4: 3/4;--wp--preset--aspect-ratio--3-2: 3/2;--wp--preset--aspect-ratio--2-3: 2/3;--wp--preset--aspect-ratio--16-9: 16/9;--wp--preset--aspect-ratio--9-16: 9/16;--wp--preset--color--black: #000000;--wp--preset--color--cyan-bluish-gray: #abb8c3;--wp--preset--color--white: #ffffff;--wp--preset--color--pale-pink: #f78da7;--wp--preset--color--vivid-red: #cf2e2e;--wp--preset--color--luminous-vivid-orange: #ff6900;--wp--preset--color--luminous-vivid-amber: #fcb900;--wp--preset--color--light-green-cyan: #7bdcb5;--wp--preset--color--vivid-green-cyan: #00d084;--wp--preset--color--pale-cyan-blue: #8ed1fc;--wp--preset--color--vivid-cyan-blue: #0693e3;--wp--preset--color--vivid-purple: #9b51e0;--wp--preset--gradient--vivid-cyan-blue-to-vivid-purple: linear-gradient(135deg,rgba(6,147,227,1) 0%,rgb(155,81,224) 100%);--wp--preset--gradient--light-green-cyan-to-vivid-green-cyan: linear-gradient(135deg,rgb(122,220,180) 0%,rgb(0,208,130) 100%);--wp--preset--gradient--luminous-vivid-amber-to-luminous-vivid-orange: linear-gradient(135deg,rgba(252,185,0,1) 0%,rgba(255,105,0,1) 100%);--wp--preset--gradient--luminous-vivid-orange-to-vivid-red: linear-gradient(135deg,rgba(255,105,0,1) 0%,rgb(207,46,46) 100%);--wp--preset--gradient--very-light-gray-to-cyan-bluish-gray: linear-gradient(135deg,rgb(238,238,238) 0%,rgb(169,184,195) 100%);--wp--preset--gradient--cool-to-warm-spectrum: linear-gradient(135deg,rgb(74,234,220) 0%,rgb(151,120,209) 20%,rgb(207,42,186) 40%,rgb(238,44,130) 60%,rgb(251,105,98) 80%,rgb(254,248,76) 100%);--wp--preset--gradient--blush-light-purple: linear-gradient(135deg,rgb(255,206,236) 0%,rgb(152,150,240) 100%);--wp--preset--gradient--blush-bordeaux: linear-gradient(135deg,rgb(254,205,165) 0%,rgb(254,45,45) 50%,rgb(107,0,62) 100%);--wp--preset--gradient--luminous-dusk: linear-gradient(135deg,rgb(255,203,112) 0%,rgb(199,81,192) 50%,rgb(65,88,208) 100%);--wp--preset--gradient--pale-ocean: linear-gradient(135deg,rgb(255,245,203) 0%,rgb(182,227,212) 50%,rgb(51,167,181) 100%);--wp--preset--gradient--electric-grass: linear-gradient(135deg,rgb(202,248,128) 0%,rgb(113,206,126) 100%);--wp--preset--gradient--midnight: linear-gradient(135deg,rgb(2,3,129) 0%,rgb(40,116,252) 100%);--wp--preset--font-size--small: 13px;--wp--preset--font-size--medium: 20px;--wp--preset--font-size--large: 36px;--wp--preset--font-size--x-large: 42px;--wp--preset--spacing--20: 0.44rem;--wp--preset--spacing--30: 0.67rem;--wp--preset--spacing--40: 1rem;--wp--preset--spacing--50: 1.5rem;--wp--preset--spacing--60: 2.25rem;--wp--preset--spacing--70: 3.38rem;--wp--preset--spacing--80: 5.06rem;--wp--preset--shadow--natural: 6px 6px 9px rgba(0, 0, 0, 0.2);--wp--preset--shadow--deep: 12px 12px 50px rgba(0, 0, 0, 0.4);--wp--preset--shadow--sharp: 6px 6px 0px rgba(0, 0, 0, 0.2);--wp--preset--shadow--outlined: 6px 6px 0px -3px rgba(255, 255, 255, 1), 6px 6px rgba(0, 0, 0, 1);--wp--preset--shadow--crisp: 6px 6px 0px rgba(0, 0, 0, 1);}:where(.is-layout-flex){gap: 0.5em;}:where(.is-layout-grid){gap: 0.5em;}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}:where(.wp-block-columns.is-layout-flex){gap: 2em;}:where(.wp-block-columns.is-layout-grid){gap: 2em;}:where(.wp-block-post-template.is-layout-flex){gap: 1.25em;}:where(.wp-block-post-template.is-layout-grid){gap: 1.25em;}.has-black-color{color: var(--wp--preset--color--black) !important;}.has-cyan-bluish-gray-color{color: var(--wp--preset--color--cyan-bluish-gray) !important;}.has-white-color{color: var(--wp--preset--color--white) !important;}.has-pale-pink-color{color: var(--wp--preset--color--pale-pink) !important;}.has-vivid-red-color{color: var(--wp--preset--color--vivid-red) !important;}.has-luminous-vivid-orange-color{color: var(--wp--preset--color--luminous-vivid-orange) !important;}.has-luminous-vivid-amber-color{color: var(--wp--preset--color--luminous-vivid-amber) !important;}.has-light-green-cyan-color{color: var(--wp--preset--color--light-green-cyan) !important;}.has-vivid-green-cyan-color{color: var(--wp--preset--color--vivid-green-cyan) !important;}.has-pale-cyan-blue-color{color: var(--wp--preset--color--pale-cyan-blue) !important;}.has-vivid-cyan-blue-color{color: var(--wp--preset--color--vivid-cyan-blue) !important;}.has-vivid-purple-color{color: var(--wp--preset--color--vivid-purple) !important;}.has-black-background-color{background-color: var(--wp--preset--color--black) !important;}.has-cyan-bluish-gray-background-color{background-color: var(--wp--preset--color--cyan-bluish-gray) !important;}.has-white-background-color{background-color: var(--wp--preset--color--white) !important;}.has-pale-pink-background-color{background-color: var(--wp--preset--color--pale-pink) !important;}.has-vivid-red-background-color{background-color: var(--wp--preset--color--vivid-red) !important;}.has-luminous-vivid-orange-background-color{background-color: var(--wp--preset--color--luminous-vivid-orange) !important;}.has-luminous-vivid-amber-background-color{background-color: var(--wp--preset--color--luminous-vivid-amber) !important;}.has-light-green-cyan-background-color{background-color: var(--wp--preset--color--light-green-cyan) !important;}.has-vivid-green-cyan-background-color{background-color: var(--wp--preset--color--vivid-green-cyan) !important;}.has-pale-cyan-blue-background-color{background-color: var(--wp--preset--color--pale-cyan-blue) !important;}.has-vivid-cyan-blue-background-color{background-color: var(--wp--preset--color--vivid-cyan-blue) !important;}.has-vivid-purple-background-color{background-color: var(--wp--preset--color--vivid-purple) !important;}.has-black-border-color{border-color: var(--wp--preset--color--black) !important;}.has-cyan-bluish-gray-border-color{border-color: var(--wp--preset--color--cyan-bluish-gray) !important;}.has-white-border-color{border-color: var(--wp--preset--color--white) !important;}.has-pale-pink-border-color{border-color: var(--wp--preset--color--pale-pink) !important;}.has-vivid-red-border-color{border-color: var(--wp--preset--color--vivid-red) !important;}.has-luminous-vivid-orange-border-color{border-color: var(--wp--preset--color--luminous-vivid-orange) !important;}.has-luminous-vivid-amber-border-color{border-color: var(--wp--preset--color--luminous-vivid-amber) !important;}.has-light-green-cyan-border-color{border-color: var(--wp--preset--color--light-green-cyan) !important;}.has-vivid-green-cyan-border-color{border-color: var(--wp--preset--color--vivid-green-cyan) !important;}.has-pale-cyan-blue-border-color{border-color: var(--wp--preset--color--pale-cyan-blue) !important;}.has-vivid-cyan-blue-border-color{border-color: var(--wp--preset--color--vivid-cyan-blue) !important;}.has-vivid-purple-border-color{border-color: var(--wp--preset--color--vivid-purple) !important;}.has-vivid-cyan-blue-to-vivid-purple-gradient-background{background: var(--wp--preset--gradient--vivid-cyan-blue-to-vivid-purple) !important;}.has-light-green-cyan-to-vivid-green-cyan-gradient-background{background: var(--wp--preset--gradient--light-green-cyan-to-vivid-green-cyan) !important;}.has-luminous-vivid-amber-to-luminous-vivid-orange-gradient-background{background: var(--wp--preset--gradient--luminous-vivid-amber-to-luminous-vivid-orange) !important;}.has-luminous-vivid-orange-to-vivid-red-gradient-background{background: var(--wp--preset--gradient--luminous-vivid-orange-to-vivid-red) !important;}.has-very-light-gray-to-cyan-bluish-gray-gradient-background{background: var(--wp--preset--gradient--very-light-gray-to-cyan-bluish-gray) !important;}.has-cool-to-warm-spectrum-gradient-background{background: var(--wp--preset--gradient--cool-to-warm-spectrum) !important;}.has-blush-light-purple-gradient-background{background: var(--wp--preset--gradient--blush-light-purple) !important;}.has-blush-bordeaux-gradient-background{background: var(--wp--preset--gradient--blush-bordeaux) !important;}.has-luminous-dusk-gradient-background{background: var(--wp--preset--gradient--luminous-dusk) !important;}.has-pale-ocean-gradient-background{background: var(--wp--preset--gradient--pale-ocean) !important;}.has-electric-grass-gradient-background{background: var(--wp--preset--gradient--electric-grass) !important;}.has-midnight-gradient-background{background: var(--wp--preset--gradient--midnight) !important;}.has-small-font-size{font-size: var(--wp--preset--font-size--small) !important;}.has-medium-font-size{font-size: var(--wp--preset--font-size--medium) !important;}.has-large-font-size{font-size: var(--wp--preset--font-size--large) !important;}.has-x-large-font-size{font-size: var(--wp--preset--font-size--x-large) !important;} :where(.wp-block-post-template.is-layout-flex){gap: 1.25em;}:where(.wp-block-post-template.is-layout-grid){gap: 1.25em;} :where(.wp-block-columns.is-layout-flex){gap: 2em;}:where(.wp-block-columns.is-layout-grid){gap: 2em;} :root :where(.wp-block-pullquote){font-size: 1.5em;line-height: 1.6;} </style> <link rel='stylesheet' id='pb-accordion-blocks-style-css' href='https://www.sdss.org/wp-content/plugins/accordion-blocks/build/index.css?ver=1.5.0' media='all' /> <style id='darkmodetg-inline-css'> html{opacity:1}html.dmtg-fade{opacity:0;background:#000000}.darkmode--activated embed,.darkmode--activated iframe,.darkmode--activated img,.darkmode--activated video{filter:invert(100%)}.darkmode--activated embed:fullscreen,.darkmode--activated iframe:fullscreen,.darkmode--activated video:fullscreen{filter:invert(0%)}.darkmode--activated [style*="background-image: url"],.darkmode--activated [style*="background-image:url"]{filter:invert(100%)}.darkmode--activated .wp-block-cover[style*="background-image: url"] .wp-block-cover[style*="background-image: url"],.darkmode--activated .wp-block-cover[style*="background-image: url"] .wp-block-cover[style*="background-image:url"],.darkmode--activated .wp-block-cover[style*="background-image: url"] embed,.darkmode--activated .wp-block-cover[style*="background-image: url"] figure[class*=wp-duotone-],.darkmode--activated .wp-block-cover[style*="background-image: url"] iframe,.darkmode--activated .wp-block-cover[style*="background-image: url"] img,.darkmode--activated .wp-block-cover[style*="background-image: url"] video,.darkmode--activated .wp-block-cover[style*="background-image:url"] .wp-block-cover[style*="background-image: url"],.darkmode--activated .wp-block-cover[style*="background-image:url"] .wp-block-cover[style*="background-image:url"],.darkmode--activated .wp-block-cover[style*="background-image:url"] embed,.darkmode--activated .wp-block-cover[style*="background-image:url"] figure[class*=wp-duotone-],.darkmode--activated .wp-block-cover[style*="background-image:url"] iframe,.darkmode--activated .wp-block-cover[style*="background-image:url"] img,.darkmode--activated .wp-block-cover[style*="background-image:url"] video{filter:invert(0)}.darkmode--activated figure[class*=wp-duotone-]{filter:invert(1)}body.custom-background.darkmode--activated .darkmode-background{background:#fff;mix-blend-mode:difference}.darkmode--activated .stssm-social-icons{filter:invert(100%)}.darkmode--activated .dmt-filter-1{filter:invert(1)!important}.darkmode--activated .dmt-filter-0{filter:invert(0)!important} </style> <link rel='stylesheet' id='galaxis-style-css' href='https://www.sdss.org/wp-content/themes/galaxis/style.min.css?ver=1.8.3' media='all' /> <link rel='stylesheet' id='child-style-css' href='https://www.sdss.org/wp-content/themes/sdss_org_wp_theme/style.css?ver=1.1.2' media='all' /> <link rel='stylesheet' id='galaxis-fonts-css' href='https://www.sdss.org/wp-content/fonts/f6df4f4615a3a6dc50eed7bcc81f60ac.css' media='all' /> <script src="https://www.sdss.org/wp-content/plugins/google-analytics-for-wordpress/assets/js/frontend-gtag.min.js?ver=8.28.0" id="monsterinsights-frontend-script-js"></script> <script data-cfasync="false" data-wpfc-render="false" id='monsterinsights-frontend-script-js-extra'>var monsterinsights_frontend = {"js_events_tracking":"true","download_extensions":"doc,pdf,ppt,zip,xls,docx,pptx,xlsx","inbound_paths":"[{\"path\":\"\\\/go\\\/\",\"label\":\"affiliate\"},{\"path\":\"\\\/recommend\\\/\",\"label\":\"affiliate\"}]","home_url":"https:\/\/www.sdss.org","hash_tracking":"false","v4_id":"G-5BJ0FDW1X0"};</script> <script src="https://www.sdss.org/wp-includes/js/jquery/jquery.min.js?ver=3.7.1" id="jquery-core-js"></script> <script src="https://www.sdss.org/wp-includes/js/jquery/jquery-migrate.min.js?ver=3.4.1" id="jquery-migrate-js"></script> <script id="darkmodetg-fade-js-after"> ("true"===window.localStorage.darkmode)&&document.documentElement.classList.add("dmtg-fade"); </script> <script src="https://www.sdss.org/wp-content/plugins/wp-quicklatex/js/wp-quicklatex-frontend.js?ver=1.0" id="wp-quicklatex-frontend-js"></script> <link rel="https://api.w.org/" href="https://www.sdss.org/wp-json/" /><link rel="alternate" title="JSON" type="application/json" href="https://www.sdss.org/wp-json/wp/v2/pages/3115" /><link rel="EditURI" type="application/rsd+xml" title="RSD" href="https://www.sdss.org/xmlrpc.php?rsd" /> <meta name="generator" content="WordPress 6.6" /> <link rel='shortlink' href='https://www.sdss.org/?p=3115' /> <link rel="alternate" title="oEmbed (JSON)" type="application/json+oembed" href="https://www.sdss.org/wp-json/oembed/1.0/embed?url=https%3A%2F%2Fwww.sdss.org%2Fdr18%2Ftutorials%2Fconversions%2F" /> <link rel="alternate" title="oEmbed (XML)" type="text/xml+oembed" href="https://www.sdss.org/wp-json/oembed/1.0/embed?url=https%3A%2F%2Fwww.sdss.org%2Fdr18%2Ftutorials%2Fconversions%2F&format=xml" /> <style type="text/css">.broken_link, a.broken_link { text-decoration: line-through; }</style><style id="custom-background-css"> body.custom-background { background-color: #867dba; } </style> <link rel="icon" href="https://www.sdss.org/wp-content/uploads/2022/04/cropped-cropped-site_icon_SDSSV-32x32.png" sizes="32x32" /> <link rel="icon" href="https://www.sdss.org/wp-content/uploads/2022/04/cropped-cropped-site_icon_SDSSV-192x192.png" sizes="192x192" /> <link rel="apple-touch-icon" href="https://www.sdss.org/wp-content/uploads/2022/04/cropped-cropped-site_icon_SDSSV-180x180.png" /> <meta name="msapplication-TileImage" content="https://www.sdss.org/wp-content/uploads/2022/04/cropped-cropped-site_icon_SDSSV-270x270.png" /> <script src="https://kit.fontawesome.com/35ce0f3af3.js" crossorigin="anonymous"></script> <script type="text/javascript" src="/wp-content/plugins/sdss_wp_shortcodes/authorhider.js"></script> <script type="text/javascript" src="/wp-content/plugins/sdss_wp_shortcodes/vacsearch.js"></script> </head> <body class="page-template page-template-page-templates page-template-template-right-sidebar page-template-page-templatestemplate-right-sidebar-php page page-id-3115 page-child parent-pageid-519 custom-background wp-custom-logo wp-embed-responsive"> <div id="page" class="site"> <a class="skip-link screen-reader-text" href="#content">Skip to content</a> <header id="header" class="site-header"> <div class="site-topbar"> <div class="site-topbar__wrap wrapper"> <div class="site-topbar-text site-topbar__left"> <a href="/dr18/">Data Release 18</a> is here! </div> </div> </div> <div class="site-menu-content site-menu-content--sticky"> <div class="site-menu-content__wrap wrapper"> <div class="site-branding gx-no-branding-text"> <a href="https://www.sdss.org/" class="custom-logo-link" rel="home"><img width="252" height="117" src="https://www.sdss.org/wp-content/uploads/2022/09/sdss-new-logo-72dpi.png" class="custom-logo" alt="SDSS" decoding="async" /></a> </div> <nav id="site-navigation" class="main-navigation"> <button type="button" class="menu-button menu-toggle" aria-controls="primary-menu" aria-expanded="false"> <span class="screen-reader-text">Primary Menu</span> <span class="main-navigation__icon"> <span class="main-navigation__icon__middle"></span> </span> </button> <div class="primary-menu-container"><ul id="primary-menu" class="menu"><li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-152" class="menu-item menu-item-type-post_type menu-item-object-page current-page-ancestor menu-item-152 nav-item"><a title="Data" href="https://www.sdss.org/dr18/">Data</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-153" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-has-children menu-item-153 nav-item"><a title="Mappers" href="https://www.sdss.org/mappers/" aria-expanded="false" id="menu-item-dropdown-153">Mappers</a><button type="button" class="menu-button menu-arrow-button"><span class="screen-reader-text menu-arrow-button-show">Expand Mappers submenu</span><span aria-hidden="true" class="screen-reader-text menu-arrow-button-hide">Collapse Mappers submenu</span><i class="sub-menu-arrow" aria-hidden="true"><svg class="svg-icon" width="20" height="20" aria-hidden="true" role="img" focusable="false" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M10 6L8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></i></button> <ul class="sub-menu"> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-887" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-887 nav-item"><a title="About Milky Way Mapper" href="https://www.sdss.org/dr18/mwm/about/">About Milky Way Mapper</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-885" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-885 nav-item"><a title="About Local Volume Mapper" href="https://www.sdss.org/dr18/lvm/about/">About Local Volume Mapper</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-884" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-884 nav-item"><a title="About Black Hole Mapper" href="https://www.sdss.org/dr18/bhm/about/">About Black Hole Mapper</a></li> </ul> </li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-157" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-157 nav-item"><a title="Instruments" href="https://www.sdss.org/instruments/">Instruments</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-158" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-158 nav-item"><a title="Collaboration" href="https://www.sdss.org/collaboration/">Collaboration</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-159" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-has-children menu-item-159 nav-item"><a title="Science" href="https://www.sdss.org/science/" aria-expanded="false" id="menu-item-dropdown-159">Science</a><button type="button" class="menu-button menu-arrow-button"><span class="screen-reader-text menu-arrow-button-show">Expand Science submenu</span><span aria-hidden="true" class="screen-reader-text menu-arrow-button-hide">Collapse Science submenu</span><i class="sub-menu-arrow" aria-hidden="true"><svg class="svg-icon" width="20" height="20" aria-hidden="true" role="img" focusable="false" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M10 6L8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></i></button> <ul class="sub-menu"> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-162" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-162 nav-item"><a title="Results" href="https://www.sdss.org/science/">Results</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-3024" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-3024 nav-item"><a title="News" href="https://www.sdss.org/news/">News</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-160" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-160 nav-item"><a title="Publications" href="https://www.sdss.org/science/publications/">Publications</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-3030" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-3030 nav-item"><a title="Science Blog" href="https://www.sdss.org/blog/">Science Blog</a></li> </ul> </li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-161" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-161 nav-item"><a title="Education" href="https://www.sdss.org/education/">Education</a></li> <li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement" id="menu-item-538" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-538 nav-item"><a title="Contact" href="https://www.sdss.org/contact-us/">Contact</a></li> </ul></div> </nav> </div> </div> <nav id="secondary-navigation" class="wrapper"> <div class="secondary-menu-container"> <ul id="menu-data-release-19" class="secondary-menu"> <li id="menu-item-4010" class="menu-item menu-item-type-custom menu-item-object-custom current-menu-item menu-item-4010"> <a href="/dr18/" aria-current="page"><strong>DR18</strong></a> </li> <li id="menu-item-550" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-550"> <a href="/dr18/data_access/">Data Access</a> </li> <li id="menu-item-543" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-543"> <a href="/dr18/bhm/">BHM</a> </li> <li id="menu-item-541" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-541"> <a href="/dr18/mwm/">MWM</a> </li> <li id="menu-item-2403" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-2403"> <a href="/dr18/lvm/about/">LVM</a> </li> <li id="menu-item-548" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-548"> <a href="/dr18/imaging/">Imaging</a> </li> <li id="menu-item-549" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-549"> <a href="/dr18/completed_surveys/"><span class="tooltip"><span class="anchortext">Completed Surveys</span><div class="tooltiptext" id="completed">APOGEE, (e)BOSS,<br>MaNGA, SDSS-I/-II</div></span></a> </li> <li id="menu-item-544" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-544"> <a href="/dr18/targeting/">Targeting</a> </li> <li id="menu-item-545" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-545"> <a href="/dr18/software/">Software</a> </li> <li id="menu-item-547" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-547"> <a href="/dr18/tutorials/">Tutorials</a> </li> <li id="menu-item-546" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-546"> <a href="/dr18/help/">Help</a> </li> </ul> </div> </nav> <div id='breadsearch' class='wrapper'> <div class='gx-card-content'> <div class='crumbs'><ul><li><a href='https://www.sdss.org/dr18/'>DR18</a></li><li><a href='https://www.sdss.org/dr18/tutorials/'>Tutorials</a></li><li><strong>Conversions</strong></li></ul></div> <div class='searcher'><section id="block-3" class="widget widget_block widget_search"><form role="search" method="get" action="https://www.sdss.org/" class="wp-block-search__button-inside wp-block-search__icon-button wp-block-search" ><label class="wp-block-search__label screen-reader-text" for="wp-block-search__input-1" >Search</label><div class="wp-block-search__inside-wrapper " ><input class="wp-block-search__input" id="wp-block-search__input-1" placeholder="Search..." value="" type="search" name="s" required /><button aria-label="Search" class="wp-block-search__button has-icon wp-element-button" type="submit" ><svg class="search-icon" viewBox="0 0 24 24" width="24" height="24"> <path d="M13 5c-3.3 0-6 2.7-6 6 0 1.4.5 2.7 1.3 3.7l-3.8 3.8 1.1 1.1 3.8-3.8c1 .8 2.3 1.3 3.7 1.3 3.3 0 6-2.7 6-6S16.3 5 13 5zm0 10.5c-2.5 0-4.5-2-4.5-4.5s2-4.5 4.5-4.5 4.5 2 4.5 4.5-2 4.5-4.5 4.5z"></path> </svg></button></div></form></aside></div> </div> </div> </header> <div id="content" class="site-content"> <div class="wrapper u-t-margin"> <div class="columns columns--gutters"> <div id="primary" class="content-area columns__md-8 u-b-margin"> <main id="main" class="site-main"> <article id="post-3115" class="gx-card post-3115 page type-page status-publish hentry"> <div class="gx-card-content"> <header class="entry-header"> <h1 class="entry-title">Wavelength and Magnitude Conversions</h1> </header> <div class="entry-content"> <div class='toc toc-right'><div class="wp-block-pb-accordion-item c-accordion__item js-accordion-item no-js toc-label" data-initially-open="1" data-click-to-close="true" data-auto-close="true" data-scroll="false" data-scroll-offset="0" id="div-id-43251515-77f0-42bb-920e-6a42b86a0f87"><div id="at-43251515-77f0-42bb-920e-6a42b86a0f87" class="c-accordion__title js-accordion-controller toc-label-accordion" role="button">On this page</div><div id="ac-43251515-77f0-42bb-920e-6a42b86a0f87" class="c-accordion__content"><ul><li class='forh2' ><a href='#vacuum'>Conversion between vacuum and air wavelengths</a></li><li class='forh2' ><a href='#SDSStoAB'>Conversion from SDSS <em>ugriz</em> magnitudes to AB <em>ugriz</em> magnitudes</a></li></ul></div></div></div> <p>This page gives information about how to convert between the wavelength and magnitude conventions used by the SDSS and other systems.</p> <h2 class="wp-block-heading" id="vacuum">Conversion between vacuum and air wavelengths</h2> <p>The SDSS data describing spectral line wavelengths use vacuum wavelengths. However, the wavelengths of atomic transitions are usually quoted at standard temperature and pressure (S.T.P.); this is how the <a rel="noreferrer noopener" href="https://hbcp.chemnetbase.com/faces/contents/ContentsSearch.xhtml;jsessionid=EE07131D6EF4D3D058D21CEE2DDE22A0" target="_blank">CRC Handbook of Chemistry and Physics</a> lists them for any transitions redward of 2000 脜ngstr枚ms.</p> <p>Thus, recognizing spectral lines associated with atomic transitions may require converting the SDSS data to the equivalent values at S.T.P.</p> <p>Since Data Release 9 (DR9) in 2012, the SDSS has used the following equation, based on the formulas given in <a href="https://ui.adsabs.harvard.edu/abs/1996ApOpt..35.1566C/abstract" target="_blank" rel="noreferrer noopener">Ciddor (1996)</a>, to convert from vacuum (VAC) wavelengths in 脜ngstr枚ms to air (AIR) wavelengths:</p> <pre class="wp-block-code"><code>AIR = VAC / ( 1.0 + 5.792105E-2/(238.0185 - (1E4/VAC)^2) + 1.67917E-3/( 57.362 - (1E4/VAC)^2))</code></pre> <h3 class="wp-block-heading" id="transitiontable">Air and Vacuum Wavelength of some Common Transitions</h3> <figure class="wp-block-table"><table><tbody><tr><td><strong>Line</strong></td><td><strong>Air</strong></td><td><strong>Vacuum</strong></td></tr><tr><td>H-beta</td><td>4861.325</td><td>4862.683</td></tr><tr><td>[O III]</td><td>4958.911</td><td>4960.295</td></tr><tr><td>[O III]</td><td>5006.843</td><td>5008.239</td></tr><tr><td>[N II]</td><td>6548.05</td><td>6549.86</td></tr><tr><td>H-alpha</td><td>6562.801</td><td>6564.614</td></tr><tr><td>[N II]</td><td>6583.45</td><td>6585.27</td></tr><tr><td>[S II]</td><td>6716.44</td><td>6718.29</td></tr><tr><td>[S II]</td><td>6730.82</td><td>6732.68</td></tr></tbody></table></figure> <p>Note also that the wavelengths are shifted such that measured velocities will be relative to the solar system barycentric at the mid-point of each exposure (using TAI-BEG + 0.5 * EXPTIME from the header).</p> <h2 class="wp-block-heading" id="SDSStoAB">Conversion from SDSS <em>ugriz</em> magnitudes to AB <em>ugriz</em> magnitudes</h2> <p>The SDSS photometry is intended to be on the AB system <a target="_blank" href="http://ui.adsabs.harvard.edu/abs/1983ApJ...266..713O" rel="noreferrer noopener">(Oke & Gunn 1983)</a>, by which a magnitude 0 object should have the same counts as a source of F<sub>谓</sub> = 3631 Jy. However, this is known not to be exactly true, such that the photometric zeropoints are slightly off the AB standard. We continue to work to pin down these shifts. Our present estimate, based on comparison to the STIS standards of <a target="_blank" href="http://ui.adsabs.harvard.edu/abs/2001AJ....122.2118B" rel="noreferrer noopener">Bohlin, Dickinson, & Calzetti (2001)</a> and confirmed by SDSS photometry and spectroscopy of fainter hot white dwarfs, is that the <var>u</var> band zeropoint is in error by 0.04 mag, <var>u</var><sub>AB</sub> = <var>u</var><sub>SDSS</sub> – 0.04 mag, and that <var>g, r</var>, and <var>i</var> are close to AB. The <var>z</var> band zeropoint is not as certain at this time, but there is mild evidence that it may be shifted by about 0.02 mag in the sense <var>z</var><sub>AB</sub> = <var>z</var><sub>SDSS</sub> + 0.02 mag.</p> <p>The large shift in the <var>u</var> band was expected because the adopted magnitude of the SDSS standard BD+17 in <a target="_blank" href="http://adsabs.harvard.edu/abs/1996AJ....111.1748F" rel="noreferrer noopener">Fukugita et al. (1996)</a> was computed at zero airmass, thereby making the assumed <var>u</var> response bluer than that of the USNO system response.</p> <p>These statements are certainly not precise to better than 0.01 mag; in addition, they depend on the system response of the SDSS 2.5-meter, which was measured by <a target="_blank" href="http://ui.adsabs.harvard.edu/abs/2010AJ....139.1628D" rel="noreferrer noopener">Doi et al. (2010)</a> and found to differ somewhat from the curves used to estimate the offsets just mentioned, and to probably be a function of time. They estimate the <em>u-g</em> change due to these differences to be at the 0.01 to 0.02 mag level.</p> <p>Note that our <em>relative</em> photometry across the sky is quite a bit better than these numbers would imply; repeat observations and simulations of the ubercal pipeline show that our calibrations are about 1% in <var>gri</var> and about 2% in <var>u</var> and <var>z</var>.</p> </div> </div> </article> </main> </div> <div class="columns__md-4"> <div class="sidebar__inner"> <aside id="secondary" class="widget-area sidebar-1 h-center-upto-md" aria-label="Sidebar"> <section id="nav_menu-40" class="widget gx-card-content u-b-margin widget_nav_menu"><h3 class="widget-title">Tutorials</h3><nav class="menu-tutorials-container" aria-label="Tutorials"><ul id="menu-tutorials" class="menu"><li id="menu-item-1329" class="menu-item menu-item-type-post_type menu-item-object-page current-page-ancestor current-page-parent menu-item-1329"><a href="https://www.sdss.org/dr18/tutorials/">Tutorials Overview</a></li> <li id="menu-item-1421" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-1421"><a href="https://www.sdss.org/dr18/tutorials/par/">Parameter Files</a></li> <li id="menu-item-1420" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-1420"><a href="https://www.sdss.org/dr18/tutorials/fitsfiles/">FITS Files</a></li> <li id="menu-item-1330" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-1330"><a href="https://www.sdss.org/dr18/tutorials/using_bitmasks/">Using Bitmasks</a></li> <li id="menu-item-3123" class="menu-item menu-item-type-post_type menu-item-object-page current-menu-item page_item page-item-3115 current_page_item menu-item-3123"><a href="https://www.sdss.org/dr18/tutorials/conversions/" aria-current="page">Wavelength and Magnitude Conversions</a></li> </ul></nav></aside>   </aside> </div> </div> </div> </div> </div> <footer id="footer" class="site-footer"> <div class="gx-footer-block-area"> <div class="wrapper"> <div class="entry-content"> <div class='toc toc-right'><div class="wp-block-pb-accordion-item c-accordion__item js-accordion-item no-js toc-label" data-initially-open="1" data-click-to-close="true" data-auto-close="true" data-scroll="false" data-scroll-offset="0" id="div-id-6bc8f8df-4f39-4960-a5c6-b7759ea40da2"><div id="at-6bc8f8df-4f39-4960-a5c6-b7759ea40da2" class="c-accordion__title js-accordion-controller toc-label-accordion" role="button">On this page</div><div id="ac-6bc8f8df-4f39-4960-a5c6-b7759ea40da2" class="c-accordion__content"><ul></ul></div></div></div> <div class="wp-block-columns is-layout-flex wp-container-core-columns-is-layout-1 wp-block-columns-is-layout-flex"> <div class="wp-block-column footmenu is-layout-flow wp-block-column-is-layout-flow"> <h3 class="wp-block-heading footmenu-label">Explore</h3> <p><a href="/dr18/" data-type="page" data-id="36">Data Release 18</a></p> <p><a href="/dr18/data_access/" data-type="page" data-id="38">Data Access</a></p> <p><a href="/dr18/tutorials/" data-type="page" data-id="519">Tutorials</a></p> <p><a href="/dr18/data_access/value-added-catalogs/" data-type="page" data-id="505">Value Added Catalogs</a></p> </div> <div class="wp-block-column footmenu is-layout-flow wp-block-column-is-layout-flow"> <h3 class="wp-block-heading footmenu-label">Learn</h3> <p><a href="/mappers/" data-type="page" data-id="68">Mappers</a></p> <p><a href="/instruments/" data-type="page" data-id="77">Instruments</a></p> <p><a href="/education/" data-type="page" data-id="91">Education</a></p> <p><a href="/science/" data-type="page" data-id="87">Science</a></p> </div> <div class="wp-block-column footmenu is-layout-flow wp-block-column-is-layout-flow"> <h3 class="wp-block-heading footmenu-label">Connect</h3> <p><a href="/contact-us/" data-type="page" data-id="32">Contact Us</a></p> <p><a href="mailto:helpdesk@sdss.org" target="_blank" rel="noreferrer noopener">Email Helpdesk</a></p> <p><a href="https://www.facebook.com/SDSSurveys/" target="_blank" rel="noreferrer noopener" class="broken_link">Facebook</a></p> <p><a href="/people/" title="">SDSS People</a></p> </div> <div class="wp-block-column footlogos is-layout-flow wp-block-column-is-layout-flow"> <p class="has-text-align-center">SDSS is supported by:</p> <div class="wp-block-image img-responsive"> <figure class="aligncenter size-large"><a href="https://www.sloan.org" target="_blank" rel="noreferrer noopener"><img loading="lazy" decoding="async" width="1024" height="200" src="/wp-content/uploads/2022/06/Logo-2B-SMALL-Gold-Blue-1024x200.png" alt="Alfred P. Sloan Foundation logo" class="wp-image-428" srcset="https://www.sdss.org/wp-content/uploads/2022/06/Logo-2B-SMALL-Gold-Blue-1024x200.png 1024w, https://www.sdss.org/wp-content/uploads/2022/06/Logo-2B-SMALL-Gold-Blue-300x59.png 300w, https://www.sdss.org/wp-content/uploads/2022/06/Logo-2B-SMALL-Gold-Blue-768x150.png 768w, https://www.sdss.org/wp-content/uploads/2022/06/Logo-2B-SMALL-Gold-Blue-1536x300.png 1536w, https://www.sdss.org/wp-content/uploads/2022/06/Logo-2B-SMALL-Gold-Blue.png 1687w" sizes="(max-width: 1024px) 100vw, 1024px" /></a></figure></div> <div class="wp-block-image img-responsive"> <figure class="aligncenter size-large"><a href="https://www.hsfoundation.org" target="_blank" rel="noreferrer noopener"><img loading="lazy" decoding="async" width="1024" height="194" src="/wp-content/uploads/2022/06/HSF_logo_horiz_RGB_760px-1024x194.png" alt="Heising-Simons Foundation logo" class="wp-image-429" srcset="https://www.sdss.org/wp-content/uploads/2022/06/HSF_logo_horiz_RGB_760px-1024x194.png 1024w, https://www.sdss.org/wp-content/uploads/2022/06/HSF_logo_horiz_RGB_760px-300x57.png 300w, https://www.sdss.org/wp-content/uploads/2022/06/HSF_logo_horiz_RGB_760px-768x146.png 768w, https://www.sdss.org/wp-content/uploads/2022/06/HSF_logo_horiz_RGB_760px-1536x291.png 1536w, https://www.sdss.org/wp-content/uploads/2022/06/HSF_logo_horiz_RGB_760px-2048x389.png 2048w" sizes="(max-width: 1024px) 100vw, 1024px" /></a></figure></div> <div class="wp-block-image img-responsive"> <figure class="aligncenter size-thumbnail"><a href="https://www.nsf.gov" target="_blank" rel="noreferrer noopener"><img loading="lazy" decoding="async" width="150" height="150" src="/wp-content/uploads/2022/06/NSF_4-Color_bitmap_Logo-380px-150x150.png" alt="U.S. National Science Foundation logo" class="wp-image-431" srcset="https://www.sdss.org/wp-content/uploads/2022/06/NSF_4-Color_bitmap_Logo-380px-150x150.png 150w, https://www.sdss.org/wp-content/uploads/2022/06/NSF_4-Color_bitmap_Logo-380px-298x300.png 298w, https://www.sdss.org/wp-content/uploads/2022/06/NSF_4-Color_bitmap_Logo-380px.png 380w" sizes="(max-width: 150px) 100vw, 150px" /></a></figure></div></div> </div> </div> </div> </div> <div class="site-footer-section site-footer__text"> <div class="wrapper"> <div class="columns columns--gutters-large v-center-mdl"> <div class="columns__md-4 columns__md-4--larger"> <p class="copyright"> Copyright 2022 | Sloan Digital Sky Survey</p> </div> </div> </div> </div> </footer> <a href="#" class="back-to-top"><span class="screen-reader-text">Back to Top</span></a> </div> <style id='core-block-supports-inline-css'> .wp-container-core-columns-is-layout-1{flex-wrap:nowrap;} </style> <script src="https://www.sdss.org/wp-content/plugins/accordion-blocks/js/accordion-blocks.min.js?ver=1.5.0" id="pb-accordion-blocks-frontend-script-js"></script> <script src="https://www.sdss.org/wp-content/plugins/dark-mode-toggle/assets/js/darkmode-js.min.js?ver=1.4.5" id="darkmode-js-js"></script> <script id="darkmodetg-js-extra"> var darkmodetg = {"config":{"bottom":"32px","left":"32px","top":"unset","right":"unset","width":"44px","height":"44px","borderRadius":"44px","fontSize":"16px","time":"0s","backgroundColor":"transparent","buttonColorDark":"#333333","buttonColorLight":"#b3b3b3","buttonColorTDark":"#ffffff","buttonColorTLight":"#000000","saveInCookies":"1","fixFlick":"1","label":"🔥","autoMatchOsTheme":false,"buttonAriaLabel":"Toggle dark mode","overrideStyles":""}}; </script> <script src="https://www.sdss.org/wp-content/plugins/dark-mode-toggle/assets/js/dmtg.min.js?ver=1.4.5" id="darkmodetg-js"></script> <script src="https://www.sdss.org/wp-content/themes/galaxis/js/script.min.js?ver=1.8.3" id="galaxis-script-js"></script> <script src="https://www.sdss.org/wp-content/themes/galaxis/js/ResizeObserver.min.js?ver=1.5.1" id="resize-observer-polyfill-js"></script> <script src="https://www.sdss.org/wp-content/themes/galaxis/js/sticky-sidebar.min.js?ver=1.1.1" id="sticky-sidebar-js"></script> <script id="sticky-sidebar-js-after"> try{new StickySidebar(".site-content > .wrapper > .columns > .columns__md-4",{topSpacing:100,bottomSpacing:0,containerSelector:".site-content > .wrapper > .columns",innerWrapperSelector:".sidebar__inner",minWidth:799});}catch(e){} </script> </body> </html>