Celestial equator: Difference between revisions
imported>Waster m Milankovitch cycles (and minor effect of other celestial bodies) cause the variation in axis and orbit over these time scales. |
→See also: already linked |
||
| Line 3: | Line 3: | ||
[[File:AxialTiltObliquity.png|right|thumb|300px|The celestial equator is currently inclined by about 23.44° to the [[ecliptic]] plane. The image shows the relations between Earth's [[axial tilt]] (or ''obliquity''), [[rotation|rotation axis]], and [[orbital plane]].]] | [[File:AxialTiltObliquity.png|right|thumb|300px|The celestial equator is currently inclined by about 23.44° to the [[ecliptic]] plane. The image shows the relations between Earth's [[axial tilt]] (or ''obliquity''), [[rotation|rotation axis]], and [[orbital plane]].]] | ||
The '''celestial equator''' is the [[great circle]] of the imaginary [[celestial sphere]] on the [[coplanarity|same plane]] as the [[equator]] of [[Earth]]. By extension, it is also a [[plane of reference]] in the [[equatorial coordinate system | The '''celestial equator''' is the [[great circle]] of the imaginary [[celestial sphere]] on the [[coplanarity|same plane]] as the [[equator]] of [[Earth]]. By extension, it is also a [[plane of reference]] in the [[equatorial coordinate system]].<ref>{{Cite web | ||
| title = Celestial Equator | | title = Celestial Equator | ||
| url=http://scienceworld.wolfram.com/astronomy/CelestialEquator.html | | url=http://scienceworld.wolfram.com/astronomy/CelestialEquator.html | ||
| Line 24: | Line 24: | ||
| 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 earth, but they [[culmination|culminate]] | [[Astronomical object]]s near the celestial equator appear above the horizon from most places on 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%" | ||
| Line 48: | Line 48: | ||
*[[Aquarius (constellation)|Aquarius]] | *[[Aquarius (constellation)|Aquarius]] | ||
|} | |} | ||
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 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 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== | ||
* [[Celestial pole]] | * [[Celestial pole]] | ||
* [[Declination]] | * [[Declination]] | ||
Revision as of 12:52, 5 June 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 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 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 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 earth, but they culminate highest near the equator. The celestial equator currently passes through these constellations:[4]
|
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.
Celestial bodies other than Earth also have similarly defined celestial equators.[5][6]