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Available in 39 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-39" 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">39 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/%D9%86%D8%B8%D8%A7%D9%85_%D8%A7%D9%84%D8%A5%D8%AD%D8%AF%D8%A7%D8%AB%D9%8A%D8%A7%D8%AA_%D8%A7%D9%84%D8%A3%D9%81%D9%82%D9%8A%D8%A9" title="نظام الإحداثيات الأفقية – Arabic" lang="ar" hreflang="ar" data-title="نظام الإحداثيات الأفقية" 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/Coordenaes_horizontales" title="Coordenaes horizontales – Asturian" lang="ast" hreflang="ast" data-title="Coordenaes horizontales" data-language-autonym="Asturianu" data-language-local-name="Asturian" class="interlanguage-link-target"><span>Asturianu</span></a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/%D0%93%D0%B0%D1%80%D1%8B%D0%B7%D0%B0%D0%BD%D1%82%D0%B0%D0%BB%D1%8C%D0%BD%D0%B0%D1%8F_%D1%81%D1%96%D1%81%D1%82%D1%8D%D0%BC%D0%B0_%D0%BA%D0%B0%D0%B0%D1%80%D0%B4%D1%8B%D0%BD%D0%B0%D1%82" title="Гарызантальная сістэма каардынат – Belarusian" lang="be" hreflang="be" data-title="Гарызантальная сістэма каардынат" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target"><span>Беларуская</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Coordenades_horitzontals" title="Coordenades horitzontals – Catalan" lang="ca" hreflang="ca" data-title="Coordenades horitzontals" 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/Obzorn%C3%ADkov%C3%A9_sou%C5%99adnice" title="Obzorníkové souřadnice – Czech" lang="cs" hreflang="cs" data-title="Obzorníkové souřadnice" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de badge-Q70894304 mw-list-item" title=""><a href="https://de.wikipedia.org/wiki/Horizontales_Koordinatensystem" title="Horizontales Koordinatensystem – German" lang="de" hreflang="de" data-title="Horizontales Koordinatensystem" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Horisondilised_koordinaadid" title="Horisondilised koordinaadid – Estonian" lang="et" hreflang="et" data-title="Horisondilised koordinaadid" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%9F%CF%81%CE%B9%CE%B6%CF%8C%CE%BD%CF%84%CE%B9%CE%B5%CF%82_%CF%83%CF%85%CE%BD%CF%84%CE%B5%CF%84%CE%B1%CE%B3%CE%BC%CE%AD%CE%BD%CE%B5%CF%82" title="Οριζόντιες συντεταγμένες – Greek" lang="el" hreflang="el" data-title="Οριζόντιες συντεταγμένες" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Coordenadas_horizontales" title="Coordenadas horizontales – Spanish" lang="es" hreflang="es" data-title="Coordenadas horizontales" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Koordenatu_horizontalen_sistema" title="Koordenatu horizontalen sistema – Basque" lang="eu" hreflang="eu" data-title="Koordenatu horizontalen sistema" 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%AF%D8%B3%D8%AA%DA%AF%D8%A7%D9%87_%D9%85%D8%AE%D8%AA%D8%B5%D8%A7%D8%AA_%D8%A7%D9%81%D9%82%DB%8C" title="دستگاه مختصات افقی – Persian" lang="fa" hreflang="fa" data-title="دستگاه مختصات افقی" 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/Syst%C3%A8me_de_coordonn%C3%A9es_horizontales" title="Système de coordonnées horizontales – French" lang="fr" hreflang="fr" data-title="Système de coordonnées horizontales" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%A7%80%ED%8F%89%EC%A2%8C%ED%91%9C%EA%B3%84" title="지평좌표계 – Korean" lang="ko" hreflang="ko" data-title="지평좌표계" 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%95%E0%A5%8D%E0%A4%B7%E0%A5%88%E0%A4%A4%E0%A4%BF%E0%A4%9C_%E0%A4%A8%E0%A4%BF%E0%A4%B0%E0%A5%8D%E0%A4%A6%E0%A5%87%E0%A4%B6%E0%A4%BE%E0%A4%82%E0%A4%95_%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%A3%E0%A4%BE%E0%A4%B2%E0%A5%80" title="क्षैतिज निर्देशांक प्रणाली – Hindi" lang="hi" hreflang="hi" data-title="क्षैतिज निर्देशांक प्रणाली" 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/Horizontski_koordinatni_sustav" title="Horizontski koordinatni sustav – Croatian" lang="hr" hreflang="hr" data-title="Horizontski koordinatni sustav" 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/Usoro_nhazi_d%E1%BB%8B_lar%E1%BB%8B%E1%BB%8B" title="Usoro nhazi dị larịị – Igbo" lang="ig" hreflang="ig" data-title="Usoro nhazi dị larịị" data-language-autonym="Igbo" data-language-local-name="Igbo" class="interlanguage-link-target"><span>Igbo</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Sistema_di_coordinate_orizzontali" title="Sistema di coordinate orizzontali – Italian" lang="it" hreflang="it" data-title="Sistema di coordinate orizzontali" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Horizontin%C4%97_koordina%C4%8Di%C5%B3_sistema" title="Horizontinė koordinačių sistema – Lithuanian" lang="lt" hreflang="lt" data-title="Horizontinė koordinačių sistema" 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/Horizont%C3%A1lis_koordin%C3%A1ta-rendszer" title="Horizontális koordináta-rendszer – Hungarian" lang="hu" hreflang="hu" data-title="Horizontális koordináta-rendszer" 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%A5%D0%BE%D1%80%D0%B8%D0%B7%D0%BE%D0%BD%D1%82%D1%81%D0%BA%D0%B8_%D0%BA%D0%BE%D0%BE%D1%80%D0%B4%D0%B8%D0%BD%D0%B0%D1%82%D0%B5%D0%BD_%D1%81%D0%B8%D1%81%D1%82%D0%B5%D0%BC" title="Хоризонтски координатен систем – Macedonian" lang="mk" hreflang="mk" data-title="Хоризонтски координатен систем" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Sistem_koordinat_mengufuk" title="Sistem koordinat mengufuk – Malay" lang="ms" hreflang="ms" data-title="Sistem koordinat mengufuk" 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-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E5%9C%B0%E5%B9%B3%E5%BA%A7%E6%A8%99" title="地平座標 – Japanese" lang="ja" hreflang="ja" data-title="地平座標" 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/Horisontalkoordinater" title="Horisontalkoordinater – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Horisontalkoordinater" 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-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Uk%C5%82ad_wsp%C3%B3%C5%82rz%C4%99dnych_horyzontalnych" title="Układ współrzędnych horyzontalnych – Polish" lang="pl" hreflang="pl" data-title="Układ współrzędnych horyzontalnych" 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/Sistema_horizontal_de_coordenadas" title="Sistema horizontal de coordenadas – Portuguese" lang="pt" hreflang="pt" data-title="Sistema horizontal de coordenadas" 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/Coordonate_astronomice_orizontale" title="Coordonate astronomice orizontale – Romanian" lang="ro" hreflang="ro" data-title="Coordonate astronomice orizontale" 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%93%D0%BE%D1%80%D0%B8%D0%B7%D0%BE%D0%BD%D1%82%D0%B0%D0%BB%D1%8C%D0%BD%D0%B0%D1%8F_%D1%81%D0%B8%D1%81%D1%82%D0%B5%D0%BC%D0%B0_%D0%BA%D0%BE%D0%BE%D1%80%D0%B4%D0%B8%D0%BD%D0%B0%D1%82" title="Горизонтальная система координат – Russian" lang="ru" hreflang="ru" data-title="Горизонтальная система координат" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Horizont%C3%A1lne_s%C3%BAradnice" title="Horizontálne súradnice – Slovak" lang="sk" hreflang="sk" data-title="Horizontálne súradnice" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Horizontni_koordinatni_sistem" title="Horizontni koordinatni sistem – Slovenian" lang="sl" hreflang="sl" data-title="Horizontni koordinatni sistem" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%A5%D0%BE%D1%80%D0%B8%D0%B7%D0%BE%D0%BD%D1%82%D1%81%D0%BA%D0%B8_%D0%BA%D0%BE%D0%BE%D1%80%D0%B4%D0%B8%D0%BD%D0%B0%D1%82%D0%BD%D0%B8_%D1%81%D0%B8%D1%81%D1%82%D0%B5%D0%BC" title="Хоризонтски координатни систем – Serbian" lang="sr" hreflang="sr" data-title="Хоризонтски координатни систем" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/Horizontski_koordinatni_sistem" title="Horizontski koordinatni sistem – Serbo-Croatian" lang="sh" hreflang="sh" data-title="Horizontski koordinatni sistem" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Horisonttij%C3%A4rjestelm%C3%A4" title="Horisonttijärjestelmä – Finnish" lang="fi" hreflang="fi" data-title="Horisonttijärjestelmä" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Horisontellt_koordinatsystem" title="Horisontellt koordinatsystem – Swedish" lang="sv" hreflang="sv" data-title="Horisontellt koordinatsystem" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-tl mw-list-item"><a href="https://tl.wikipedia.org/wiki/Sistemang_pahalang_ng_mga_koordinado" title="Sistemang pahalang ng mga koordinado – Tagalog" lang="tl" hreflang="tl" data-title="Sistemang pahalang ng mga koordinado" data-language-autonym="Tagalog" data-language-local-name="Tagalog" class="interlanguage-link-target"><span>Tagalog</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%A3%E0%B8%B0%E0%B8%9A%E0%B8%9A%E0%B8%9E%E0%B8%B4%E0%B8%81%E0%B8%B1%E0%B8%94%E0%B8%82%E0%B8%AD%E0%B8%9A%E0%B8%9F%E0%B9%89%E0%B8%B2" title="ระบบพิกัดขอบฟ้า – Thai" lang="th" hreflang="th" data-title="ระบบพิกัดขอบฟ้า" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%93%D0%BE%D1%80%D0%B8%D0%B7%D0%BE%D0%BD%D1%82%D0%B0%D0%BB%D1%8C%D0%BD%D0%B0_%D1%81%D0%B8%D1%81%D1%82%D0%B5%D0%BC%D0%B0_%D0%BA%D0%BE%D0%BE%D1%80%D0%B4%D0%B8%D0%BD%D0%B0%D1%82" title="Горизонтальна система координат – Ukrainian" lang="uk" hreflang="uk" data-title="Горизонтальна система координат" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-ur mw-list-item"><a href="https://ur.wikipedia.org/wiki/%D8%A7%D9%81%D9%82%DB%8C_%D9%85%D8%AA%D9%86%D8%A7%D8%B3%D9%82_%D9%86%D8%B8%D8%A7%D9%85" title="افقی متناسق نظام – Urdu" lang="ur" hreflang="ur" data-title="افقی متناسق نظام" data-language-autonym="اردو" data-language-local-name="Urdu" class="interlanguage-link-target"><span>اردو</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/H%E1%BB%87_t%E1%BB%8Da_%C4%91%E1%BB%99_ch%C3%A2n_tr%E1%BB%9Di" title="Hệ tọa độ chân trời – Vietnamese" lang="vi" hreflang="vi" data-title="Hệ tọa độ chân trời" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E5%9C%B0%E5%B9%B3%E5%9D%90%E6%A8%99%E7%B3%BB" title="地平坐標系 – Chinese" lang="zh" hreflang="zh" data-title="地平坐標系" data-language-autonym="中文" data-language-local-name="Chinese" 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data-event-name="pinnable-header.vector-appearance.unpin">hide</button> </div> </div> </div> </nav> </div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Type of celestial coordinate system</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">Not to be confused with <a href="/wiki/Horizontal_position_representation" title="Horizontal position representation">Horizontal position representation</a>.</div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Azimuth-Altitude_schematic.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Azimuth-Altitude_schematic.svg/350px-Azimuth-Altitude_schematic.svg.png" decoding="async" width="350" height="337" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Azimuth-Altitude_schematic.svg/525px-Azimuth-Altitude_schematic.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Azimuth-Altitude_schematic.svg/700px-Azimuth-Altitude_schematic.svg.png 2x" data-file-width="436" data-file-height="420" /></a><figcaption>Horizontal coordinates use a <a href="/wiki/Celestial_sphere" title="Celestial sphere">celestial sphere</a> centered on the observer. <a href="/wiki/Azimuth" title="Azimuth">Azimuth</a> is measured <a href="/wiki/East" title="East">eastward</a> from the <a href="/wiki/True_north" title="True north">north</a> point (sometimes from the <a href="/wiki/South" title="South">south</a> point) of the <a href="/wiki/Horizon" title="Horizon">horizon</a>; altitude is the angle above the horizon.</figcaption></figure> <p>The <b>horizontal coordinate system</b> is a <a href="/wiki/Celestial_coordinate_system" class="mw-redirect" title="Celestial coordinate system">celestial coordinate system</a> that uses the observer's local <a href="/wiki/Horizon" title="Horizon">horizon</a> as the <a href="/wiki/Fundamental_plane_(spherical_coordinates)" title="Fundamental plane (spherical coordinates)">fundamental plane</a> to define two angles of a <a href="/wiki/Spherical_coordinate_system" title="Spherical coordinate system">spherical coordinate system</a>: <b>altitude</b> and <i><a href="/wiki/Azimuth" title="Azimuth">azimuth</a></i>. Therefore, the horizontal coordinate system is sometimes called the <b>az/el system</b>,<sup id="cite_ref-Keck-Az-El_1-0" class="reference"><a href="#cite_note-Keck-Az-El-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> the <b>alt/az system</b>, or the <b>alt-azimuth system</b>, among others. In an <a href="/wiki/Altazimuth_mount" title="Altazimuth mount">altazimuth mount</a> of a <a href="/wiki/Telescope" title="Telescope">telescope</a>, the instrument's two axes follow altitude and azimuth.<sup id="cite_ref-Britannica-horizon-system_2-0" class="reference"><a href="#cite_note-Britannica-horizon-system-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Definition">Definition</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Horizontal_coordinate_system&action=edit&section=1" title="Edit section: Definition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>This <a href="/wiki/Celestial_coordinate_system" class="mw-redirect" title="Celestial coordinate system">celestial coordinate system</a> divides the <a href="/wiki/Sky" title="Sky">sky</a> into two <a href="/wiki/Sphere#Hemisphere" title="Sphere">hemispheres</a>: The upper hemisphere, where objects are above the <a href="/wiki/Horizon" title="Horizon">horizon</a> and are visible, and the lower hemisphere, where objects are below the horizon and cannot be seen, since the Earth obstructs views of them.<sup id="cite_ref-geometric_horizon_footnote_3-0" class="reference"><a href="#cite_note-geometric_horizon_footnote-3"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Great_circle" title="Great circle">great circle</a> separating the hemispheres is called the <b>celestial horizon</b>, which is defined as the great circle on the celestial sphere whose plane is normal to the local gravity vector.<sup id="cite_ref-Clarke-Roy-2003_4-0" class="reference"><a href="#cite_note-Clarke-Roy-2003-4"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-geometric_horizon_footnote_3-1" class="reference"><a href="#cite_note-geometric_horizon_footnote-3"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> In practice, the horizon can be defined as the plane <a href="/wiki/Tangent" title="Tangent">tangent</a> to a quiet, liquid surface, such as a pool of <a href="/wiki/Mercury_(element)" title="Mercury (element)">mercury</a>.<sup id="cite_ref-Young-Kattawar-Parviainen-1997_5-0" class="reference"><a href="#cite_note-Young-Kattawar-Parviainen-1997-5"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> The pole of the upper hemisphere is called the <a href="/wiki/Zenith" title="Zenith">zenith</a>. The pole of the lower hemisphere is called the <a href="/wiki/Nadir" title="Nadir">nadir</a>.<sup id="cite_ref-Schombert-Earth-co-ords_6-0" class="reference"><a href="#cite_note-Schombert-Earth-co-ords-6"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p><p>The following are two independent horizontal <a href="/wiki/Angular_coordinate" class="mw-redirect" title="Angular coordinate">angular coordinates</a>: </p> <ul><li>Altitude (alt.), sometimes referred to as <a href="/wiki/Elevation_angle" class="mw-redirect" title="Elevation angle">elevation</a> (el.) or <style data-mw-deduplicate="TemplateStyles:r1238216509">.mw-parser-output .vanchor>:target~.vanchor-text{background-color:#b1d2ff}@media screen{html.skin-theme-clientpref-night .mw-parser-output .vanchor>:target~.vanchor-text{background-color:#0f4dc9}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .vanchor>:target~.vanchor-text{background-color:#0f4dc9}}</style><span class="vanchor"><span id="apparent_height"></span><span class="vanchor-text">apparent height</span></span>, is the angle between the object and the observer's local horizon. For visible objects, it is an angle between 0° and 90°.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>b<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Azimuth" title="Azimuth">Azimuth</a> (az.) is the angle of the object around the horizon, usually measured from <a href="/wiki/True_north" title="True north">true north</a> and increasing eastward. Exceptions are, for example, <a href="/wiki/European_Southern_Observatory" title="European Southern Observatory">ESO</a>'s <a href="/wiki/FITS" title="FITS">FITS</a> convention where it is measured from the south and increasing westward, or the <a href="/wiki/FITS" title="FITS">FITS</a> convention of the <a href="/wiki/Sloan_Digital_Sky_Survey" title="Sloan Digital Sky Survey">Sloan Digital Sky Survey</a> where it is measured from the south and increasing eastward.</li></ul> <p>A horizontal coordinate system should not be confused with a <i><a href="/wiki/Topocentric_coordinate_system" class="mw-redirect" title="Topocentric coordinate system">topocentric coordinate system</a></i>. Horizontal coordinates define the observer's orientation, but not location of the origin, while topocentric coordinates define the origin location, on the Earth's surface, in contrast to a <a href="/wiki/Geocentric_Celestial_Reference_System" class="mw-redirect" title="Geocentric Celestial Reference System">geocentric celestial system</a>. </p> <div class="mw-heading mw-heading2"><h2 id="General_features">General features</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Horizontal_coordinate_system&action=edit&section=2" title="Edit section: General features"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The horizontal coordinate system is fixed to a location on Earth, not the stars. Therefore, the altitude and azimuth of an object in the sky changes with time, as the object appears to drift across the sky with <a href="/wiki/Earth%27s_rotation" title="Earth's rotation">Earth's rotation</a>. In addition, since the horizontal system is defined by the observer's local horizon,<sup id="cite_ref-geometric_horizon_footnote_3-2" class="reference"><a href="#cite_note-geometric_horizon_footnote-3"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> the same object viewed from different locations on Earth at the same time will have different values of altitude and azimuth. </p><p>The <a href="/wiki/Cardinal_direction" title="Cardinal direction">cardinal points</a> on the horizon have specific values of azimuth that are helpful references. </p> <table class="wikitable" style="text-align:center"> <caption>Azimuth values for the cardinal directions </caption> <tbody><tr> <th scope="col">Cardinal point </th> <th scope="col">Azimuth </th></tr> <tr> <th scope="row">North </th> <td>0° </td></tr> <tr> <th scope="row">East </th> <td>90° </td></tr> <tr> <th scope="row">South </th> <td>180° </td></tr> <tr> <th scope="row">West </th> <td>270° </td></tr></tbody></table> <p>Horizontal coordinates are very useful for determining the rise and set times of an object in the sky. When an object's altitude is 0°, it is on the horizon.<sup id="cite_ref-geometric_horizon_footnote_3-3" class="reference"><a href="#cite_note-geometric_horizon_footnote-3"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> If at that moment its altitude is increasing, it is rising, but if its altitude is decreasing, it is setting. However, all objects on the <a href="/wiki/Celestial_sphere" title="Celestial sphere">celestial sphere</a> are subject to <a href="/wiki/Diurnal_motion" title="Diurnal motion">diurnal motion</a>, which always appears to be westward. </p><p>A northern observer can determine whether altitude is increasing or decreasing by instead considering the azimuth of the celestial object: </p> <ul><li>If the azimuth is between 0° and 180° (north–east–south), the object is rising.</li> <li>If the azimuth is between 180° and 360° (south–west–north), the object is setting.</li></ul> <p>There are the following special cases:<sup id="cite_ref-geometric_horizon_footnote_3-4" class="reference"><a href="#cite_note-geometric_horizon_footnote-3"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> </p> <ul><li>All directions are south when viewed from the <a href="/wiki/North_Pole" title="North Pole">North Pole</a>, and all directions are north when viewed from the <a href="/wiki/South_Pole" title="South Pole">South Pole</a>, so the azimuth is undefined in both locations. When viewed from either pole, a star (or any object with fixed <a href="/wiki/Equatorial_coordinates" class="mw-redirect" title="Equatorial coordinates">equatorial coordinates</a>) has constant altitude and thus <a href="/wiki/Circumpolar_star" title="Circumpolar star">never rises or sets</a>. The <a href="/wiki/Sun" title="Sun">Sun</a>, <a href="/wiki/Moon" title="Moon">Moon</a>, and <a href="/wiki/Planets" class="mw-redirect" title="Planets">planets</a> can rise or set over the span of a year when viewed from the poles because their <a href="/wiki/Declination" title="Declination">declinations</a> are constantly changing.</li> <li>When viewed from the <a href="/wiki/Equator" title="Equator">equator</a>, objects on the celestial poles stay at fixed points, perched on the horizon.</li></ul> <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=Horizontal_coordinate_system&action=edit&section=3" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1184024115">.mw-parser-output .div-col{margin-top:0.3em;column-width:30em}.mw-parser-output .div-col-small{font-size:90%}.mw-parser-output .div-col-rules{column-rule:1px solid #aaa}.mw-parser-output .div-col dl,.mw-parser-output .div-col ol,.mw-parser-output .div-col ul{margin-top:0}.mw-parser-output .div-col li,.mw-parser-output .div-col dd{page-break-inside:avoid;break-inside:avoid-column}</style><div class="div-col" style="column-width: 25em;"> <ul><li><a href="/wiki/Azimuth" title="Azimuth">Azimuth</a></li> <li><a href="/wiki/Astronomical_coordinate_systems" title="Astronomical coordinate systems">Astronomical coordinate systems</a> <ul><li><a href="/wiki/Astronomical_coordinate_systems#Converting_coordinates" title="Astronomical coordinate systems">Astronomical coordinate systems § Converting coordinates</a></li></ul></li> <li><a href="/wiki/Geocentric_coordinates" class="mw-redirect" title="Geocentric coordinates">Geocentric coordinates</a></li> <li><a href="/wiki/Horizon" title="Horizon">Horizon</a></li> <li><a href="/wiki/Vertical_and_horizontal" title="Vertical and horizontal">Vertical and horizontal</a></li> <li><a href="/wiki/Meridian_(astronomy)" title="Meridian (astronomy)">Meridian (astronomy)</a></li> <li><a href="/wiki/Sextant" title="Sextant">Sextant</a></li> <li><a href="/wiki/Solar_declination" class="mw-redirect" title="Solar declination">Solar declination</a></li> <li><a href="/wiki/Spherical_coordinate_system" title="Spherical coordinate system">Spherical coordinate system</a></li> <li><a href="/wiki/Vertical_circle" title="Vertical circle">Vertical circle</a></li> <li><a href="/wiki/Zenith" title="Zenith">Zenith</a></li></ul> </div> <div class="mw-heading mw-heading2"><h2 id="Footnotes">Footnotes</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Horizontal_coordinate_system&action=edit&section=4" title="Edit section: Footnotes"><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 reflist-lower-alpha"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-geometric_horizon_footnote-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-geometric_horizon_footnote_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-geometric_horizon_footnote_3-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-geometric_horizon_footnote_3-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-geometric_horizon_footnote_3-3"><sup><i><b>d</b></i></sup></a> <a href="#cite_ref-geometric_horizon_footnote_3-4"><sup><i><b>e</b></i></sup></a></span> <span class="reference-text">Note that the special conditions described are strictly true only regarding the <i>geometric</i> horizon. That is, the horizon as it <i>would</i> appear for an observer on a perfectly smooth Earth without an atmosphere, for an observer at <a href="/wiki/Sea-level" class="mw-redirect" title="Sea-level">sea-level</a>. In practice, the <i>apparent</i> horizon has a slight negative altitude due to the curvature of Earth, the value of which gets more negative as the observer ascends higher above <a href="/wiki/Sea_level" title="Sea level">sea level</a>. In addition, <a href="/wiki/Atmospheric_refraction" title="Atmospheric refraction">atmospheric refraction</a> causes celestial objects very close to the horizon to appear about half a degree <a href="/wiki/Looming_and_similar_refraction_phenomena" title="Looming and similar refraction phenomena">higher</a> than they would if there were no atmosphere.</span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text">Alternatively, <a href="/wiki/Zenith_angle" class="mw-redirect" title="Zenith angle">zenith angle</a> may be used instead of altitude, as they are <a href="/wiki/Complementary_angles" class="mw-redirect" title="Complementary angles">complementary angles</a> (the sum of the altitude angle and the zenith angle is 90°).</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=Horizontal_coordinate_system&action=edit&section=5" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239543626"><div class="reflist reflist-columns references-column-width" style="column-width: 25em;"> <ol class="references"> <li id="cite_note-Keck-Az-El-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-Keck-Az-El_1-0">^</a></b></span> <span class="reference-text"> <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www2.keck.hawaii.edu/inst/KSDs/40/html/ksd40-55.4.html">"(Az,El) co-ordinate system"</a>. W.M. Keck Observatory. <i><a href="/wiki/University_of_Hawaii" class="mw-redirect" title="University of Hawaii">University of Hawaii</a></i><span class="reference-accessdate">. Retrieved <span class="nowrap">2021-05-18</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=University+of+Hawaii&rft.atitle=%28Az%2CEl%29+co-ordinate+system&rft_id=http%3A%2F%2Fwww2.keck.hawaii.edu%2Finst%2FKSDs%2F40%2Fhtml%2Fksd40-55.4.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHorizontal+coordinate+system" class="Z3988"></span></span> </li> <li id="cite_note-Britannica-horizon-system-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-Britannica-horizon-system_2-0">^</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="http://www.britannica.com/EBchecked/topic/271741/horizon-system">"horizon system"</a>. <i><a href="/wiki/Encyclop%C3%A6dia_Britannica" title="Encyclopædia Britannica">Encyclopædia Britannica</a></i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=horizon+system&rft.btitle=Encyclop%C3%A6dia+Britannica&rft_id=http%3A%2F%2Fwww.britannica.com%2FEBchecked%2Ftopic%2F271741%2Fhorizon-system&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHorizontal+coordinate+system" class="Z3988"></span></span> </li> <li id="cite_note-Clarke-Roy-2003-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-Clarke-Roy-2003_4-0">^</a></b></span> <span class="reference-text"> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFClarkeRoy2003" class="citation book cs1">Clarke, D.; Roy, A.E. (2003). <a rel="nofollow" class="external text" href="http://ciencias.bogota.unal.edu.co/fileadmin/content/oan/documentos/maestria/documentos/coordenadas.pdf"><i>Astronomy: Principles and practice</i></a> <span class="cs1-format">(PDF)</span> (4th ed.). Bristol, UK: Institute of Physics Publications. p. 59. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9780750309172" title="Special:BookSources/9780750309172"><bdi>9780750309172</bdi></a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20180710011728/http://ciencias.bogota.unal.edu.co/fileadmin/content/oan/documentos/maestria/documentos/coordenadas.pdf">Archived</a> <span class="cs1-format">(PDF)</span> from the original on 2018-07-10<span class="reference-accessdate">. Retrieved <span class="nowrap">9 July</span> 2018</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Astronomy%3A+Principles+and+practice&rft.place=Bristol%2C+UK&rft.pages=59&rft.edition=4th&rft.pub=Institute+of+Physics+Publications&rft.date=2003&rft.isbn=9780750309172&rft.aulast=Clarke&rft.aufirst=D.&rft.au=Roy%2C+A.E.&rft_id=http%3A%2F%2Fciencias.bogota.unal.edu.co%2Ffileadmin%2Fcontent%2Foan%2Fdocumentos%2Fmaestria%2Fdocumentos%2Fcoordenadas.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHorizontal+coordinate+system" class="Z3988"></span></span> </li> <li id="cite_note-Young-Kattawar-Parviainen-1997-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-Young-Kattawar-Parviainen-1997_5-0">^</a></b></span> <span class="reference-text"> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFYoungKattawarParviainen1997" class="citation journal cs1">Young, Andrew T.; Kattawar, George W.; Parviainen, Pekka (1997). "Sunset science. I. The mock mirage". <i>Applied Optics</i>. <b>36</b> (12): 2689–2700. <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/1997ApOpt..36.2689Y">1997ApOpt..36.2689Y</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1364%2Fao.36.002689">10.1364/ao.36.002689</a>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/18253261">18253261</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Applied+Optics&rft.atitle=Sunset+science.+I.+The+mock+mirage&rft.volume=36&rft.issue=12&rft.pages=2689-2700&rft.date=1997&rft_id=info%3Apmid%2F18253261&rft_id=info%3Adoi%2F10.1364%2Fao.36.002689&rft_id=info%3Abibcode%2F1997ApOpt..36.2689Y&rft.aulast=Young&rft.aufirst=Andrew+T.&rft.au=Kattawar%2C+George+W.&rft.au=Parviainen%2C+Pekka&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHorizontal+coordinate+system" class="Z3988"></span></span> </li> <li id="cite_note-Schombert-Earth-co-ords-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-Schombert-Earth-co-ords_6-0">^</a></b></span> <span class="reference-text"> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSchombert" class="citation web cs1">Schombert, James. <a rel="nofollow" class="external text" href="http://abyss.uoregon.edu/~js/ast121/lectures/lec03.html">"Earth co-ordinate system"</a>. Department of Physics. <a href="/wiki/University_of_Oregon" title="University of Oregon">University of Oregon</a><span class="reference-accessdate">. Retrieved <span class="nowrap">19 March</span> 2011</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Earth+co-ordinate+system&rft.pub=University+of+Oregon&rft.aulast=Schombert&rft.aufirst=James&rft_id=http%3A%2F%2Fabyss.uoregon.edu%2F~js%2Fast121%2Flectures%2Flec03.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHorizontal+coordinate+system" class="Z3988"></span></span> </li> </ol></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Horizontal_coordinate_system&action=edit&section=6" title="Edit section: External links"><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 class="citation audio-visual cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20150512040636/http://www.youtube.com/watch?v=nA8CCqA-JlY"><i>explanations of the horizontal co-ordinate system</i></a> (video). Archived from <a rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=nA8CCqA-JlY">the original</a> on 2015-05-12 – via YouTube.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=explanations+of+the+horizontal+co-ordinate+system&rft_id=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DnA8CCqA-JlY&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHorizontal+coordinate+system" class="Z3988"></span></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist 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