Celestial equator: Difference between revisions
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| title = Celestial Equator | | title = Celestial Equator | ||
| url=http://scienceworld.wolfram.com/astronomy/CelestialEquator.html | | url=http://scienceworld.wolfram.com/astronomy/CelestialEquator.html | ||
| access-date = 5 August 2011 }}</ref> Due to Earth's [[axial tilt]], the celestial equator is currently inclined by about 23.44° with respect to the [[ecliptic]] (the plane of [[Earth's orbit]]), but has varied from about 22.0° to 24.5° over the past 5 million years<ref> | | access-date = 5 August 2011 }}</ref> Due to the Earth's [[axial tilt]], the celestial equator is currently inclined by about 23.44° with respect to the [[ecliptic]] (the plane of [[Earth's orbit]]), but has varied from about 22.0° to 24.5° over the past 5 million years<ref> | ||
{{cite journal | {{cite journal | ||
|last=Berger |first=A.L. | |last=Berger |first=A.L. | ||
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}}</ref> due to [[Milankovitch cycles]] and [[perturbation (astronomy)|perturbation]] from other planets. | }}</ref> due to [[Milankovitch cycles]] and [[perturbation (astronomy)|perturbation]] from other planets. | ||
An observer standing on Earth's [[equator]] visualizes the celestial equator as a [[semicircle]] passing through the [[zenith]], the point directly overhead. As the observer moves north (or south), the celestial equator tilts towards the opposite [[horizon]]. The celestial equator is defined to be infinitely distant (since it is on the celestial sphere); thus, the ends of the semicircle always intersect the horizon due east and due west, regardless of the observer's position on Earth. At the [[geographical pole|poles]], the celestial equator coincides with the astronomical horizon. At all [[latitude]]s, the celestial equator is a uniform arc or circle because the observer is only finitely far from the plane of the celestial equator, but infinitely far from the celestial equator itself.<ref>{{Cite book | An observer standing on the Earth's [[equator]] visualizes the celestial equator as a [[semicircle]] passing through the [[zenith]], the point directly overhead. As the observer moves north (or south), the celestial equator tilts towards the opposite [[horizon]]. The celestial equator is defined to be infinitely distant (since it is on the celestial sphere); thus, the ends of the semicircle always intersect the horizon due east and due west, regardless of the observer's position on the Earth. At the [[geographical pole|poles]], the celestial equator coincides with the astronomical horizon. At all [[latitude]]s, the celestial equator is a uniform arc or circle because the observer is only finitely far from the plane of the celestial equator, but infinitely far from the celestial equator itself.<ref>{{Cite book | ||
| last = Millar | | last = Millar | ||
| first = William | | first = William | ||
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| isbn = 978-0-521-67123-1}}</ref> | | isbn = 978-0-521-67123-1}}</ref> | ||
[[Astronomical object]]s near the celestial equator appear above the horizon from most places on | [[Astronomical object]]s near the celestial equator appear above the horizon from most places on the Earth, but they [[culmination|culminate]] highest near the equator. The celestial equator currently passes through these [[constellation]]s:<ref>{{cite web|url=https://in-the-sky.org/data/constellations_map.php|title=Map of the Constellations|last=Ford|first=Dominic|website=in-the-sky.org|access-date=1 Feb 2021}}</ref> | ||
{| width="60%" | {| width="60%" | ||
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*[[Pisces (constellation)|Pisces]] (contains the [[first point of Aries]] above its southern border) | *[[Pisces (constellation)|Pisces]] (contains the [[first point of Aries]] above its southern border) | ||
*[[Cetus]] | *[[Cetus (constellation)|Cetus]] | ||
*[[Taurus (constellation)|Taurus]] | *[[Taurus (constellation)|Taurus]] | ||
*[[Eridanus (constellation)|Eridanus]] | *[[Eridanus (constellation)|Eridanus]] | ||
*[[Orion (constellation)|Orion]] (near [[Orion's | *[[Orion (constellation)|Orion]] (near [[Orion's Belt]]) | ||
| width="20%" | | | width="20%" | | ||
*[[Monoceros (constellation)|Monoceros]] | *[[Monoceros (constellation)|Monoceros]] | ||
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|} | |} | ||
Over thousands of years, the orientation of Earth's equator and thus the constellations the celestial equator passes through will change due to [[axial precession]]. | Over thousands of years, the orientation of the Earth's equator and thus the constellations the celestial equator passes through will change due to [[axial precession]]. | ||
Celestial bodies other than Earth also have similarly defined celestial equators.<ref>{{cite journal|vauthors=Tarasashvili MV, ((Sabashvili ShA)), Tsereteli SL, Aleksidze NG|date=26 Mar 2013|title=New model of Mars surface irradiation for the climate simulation chamber 'Artificial Mars'|url=https://www.researchgate.net/publication/258789199|journal=International Journal of Astrobiology|volume=12|issue=2|pages=161–170|doi=10.1017/S1473550413000062|bibcode=2013IJAsB..12..161T|s2cid=120041831 }}</ref><ref>{{cite web|url=https://www.dlr.de/media/en/desktopdefault.aspx/tabid-4986/8423_page-7//8423_read-12880|title=Equal length of day and night on Saturn: the start of spring in the northern hemisphere|publisher=[[German Aerospace Center]]|access-date=1 Feb 2021|archive-date=28 June 2021|archive-url=https://web.archive.org/web/20210628090055/https://www.dlr.de/media/en/desktopdefault.aspx/tabid-4986/8423_page-7//8423_read-12880|url-status=dead}}</ref> | Celestial bodies other than the Earth also have similarly defined celestial equators.<ref>{{cite journal|vauthors=Tarasashvili MV, ((Sabashvili ShA)), Tsereteli SL, Aleksidze NG|date=26 Mar 2013|title=New model of Mars surface irradiation for the climate simulation chamber 'Artificial Mars'|url=https://www.researchgate.net/publication/258789199|journal=International Journal of Astrobiology|volume=12|issue=2|pages=161–170|doi=10.1017/S1473550413000062|bibcode=2013IJAsB..12..161T|s2cid=120041831 }}</ref><ref>{{cite web|url=https://www.dlr.de/media/en/desktopdefault.aspx/tabid-4986/8423_page-7//8423_read-12880|title=Equal length of day and night on Saturn: the start of spring in the northern hemisphere|publisher=[[German Aerospace Center]]|access-date=1 Feb 2021|archive-date=28 June 2021|archive-url=https://web.archive.org/web/20210628090055/https://www.dlr.de/media/en/desktopdefault.aspx/tabid-4986/8423_page-7//8423_read-12880|url-status=dead}}</ref> | ||
==See also== | ==See also== | ||
Latest revision as of 00:13, 21 September 2025
The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. By extension, it is also a plane of reference in the equatorial coordinate system.[1] Due to the Earth's axial tilt, the celestial equator is currently inclined by about 23.44° with respect to the ecliptic (the plane of Earth's orbit), but has varied from about 22.0° to 24.5° over the past 5 million years[2] due to Milankovitch cycles and perturbation from other planets.
An observer standing on the Earth's equator visualizes the celestial equator as a semicircle passing through the zenith, the point directly overhead. As the observer moves north (or south), the celestial equator tilts towards the opposite horizon. The celestial equator is defined to be infinitely distant (since it is on the celestial sphere); thus, the ends of the semicircle always intersect the horizon due east and due west, regardless of the observer's position on the Earth. At the poles, the celestial equator coincides with the astronomical horizon. At all latitudes, the celestial equator is a uniform arc or circle because the observer is only finitely far from the plane of the celestial equator, but infinitely far from the celestial equator itself.[3]
Astronomical objects near the celestial equator appear above the horizon from most places on the Earth, but they culminate highest near the equator. The celestial equator currently passes through these constellations:[4]
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Over thousands of years, the orientation of the Earth's equator and thus the constellations the celestial equator passes through will change due to axial precession.
Celestial bodies other than the Earth also have similarly defined celestial equators.[5][6]