The equator is the imaginary line that separates the northern hemisphere and the southern hemisphere of the Earth. It is an essential point of reference in geography and astronomy. Another term for equator is the "celestial equator," which is the projection of the Earth's equator onto the celestial sphere. It is also known as the "line of zero latitude," "circle of latitude," or the "equinoctial line." Other synonyms for the equator include "middle line," "belt line," and "equatorial line." The term "equinoctial circle" is also used to describe the equator as it passes through the vernal and autumnal equinoxes.