Celestial equator
The celestial equator is the
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 (reach the meridian) highest near the equator. The celestial equator currently passes through these constellations:[4]
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These are the most globally visible constellations.
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]
See also
References
- ^ "Celestial Equator". Retrieved 5 August 2011.
- ^
Berger, A.L. (1976). "Obliquity and Precession for the Last 5000000 Years". Bibcode:1976A&A....51..127B.
- ISBN 978-0-521-67123-1.
- ^ Ford, Dominic. "Map of the Constellations". in-the-sky.org. Retrieved 1 Feb 2021.
- S2CID 120041831.
- ^ "Equal length of day and night on Saturn: the start of spring in the northern hemisphere". German Aerospace Center. Retrieved 1 Feb 2021.