Celestial equator
The celestial equator is the great circle on the imaginary celestial sphere , on which it is intersected by the plane of the earth's equator . In other words: If you put a lightbulb in the center of a glass globe, the celestial equator would be the projection of the earth's equator onto the apparent celestial sphere. He divides it into a north and a south half.
Since the earth's axis is inclined to the plane of the solar system , the celestial equator intersects the ecliptic - the apparent plane of the sun's orbit around the earth - at an angle of 23.43 ° (as of November 16, 2014, inclination of the ecliptic ) . The two points of intersection are referred to as the point of spring and autumn , because the projection of the sun onto the apparent celestial sphere to the equinoxes of day and night in spring and autumn is located in them.
Places on the celestial equator have the equatorial coordinate system , the declination 0 ° and a polar distance of 90 °, its right ascension is measured from the vernal equinox.
Since the earth's axis performs a precession movement , the position of the celestial equator changes over time, and with it the direction of the vernal equinox in space.