What is Celestial equator?
[[Image:AxialTiltObliquity.png|right|thumb|350px|The celestial equator is inclined by 23.5° to the [[Ecliptic|ecliptic plane]]. The image shows the relations between Earth's [[axial tilt]] (or ''obliquity''), [[Rotation|rotation axis]] and [[Orbital plane (astronomy)|plane of orbit]].]] The '''celestial equator''' is a term in observational [[astronomy]]. It is a [[great circle]] on the imaginary [[celestial sphere]], in the same plane as the [[Earth]]'s [[equator]]. In other words, it is a projection of the terrestrial equator out into space.<ref>{{Cite web| title = Celestial Equator| url=http://scienceworld.wolfram.com/astronomy/CelestialEquator.html| access-date = 5 August 2011 }}</ref> As a result of the Earth's [[axial tilt]], the celestial equator is inclined by 23.4° with respect to the [[Ecliptic|ecliptic plane]]. An observer standing on the Earth's [[equator]] visualizes the celestial equator as a [[semicircle]] passing directly overhead through the [[zenith]]. As the observer moves north (or south), the celestial equator tilts towards the southern (or northern) horizon. At the [[Geographical pole|poles]], the celestial equator is parallel to the horizon. The observer always sees the ends of the semicircle disappear over the [[horizon]] exactly due east and due west, regardless of the observer's position on Earth. == References == {{Reflist}} {{sci-stub}} [[Category:Astronomy]]