equator

EQUA'TOR, n. [L. from oequo, to make equal.] In astronomy and geography, a great circle of the sphere, equally distant from the two poles of the world, or having the same poles as the world. It is called equator, because when the sun is in it, the days and nights are of equal length; hence it is called also the equinoctial, and when drawn on maps, globes and planispheres, it is called the equinoctial line, or simply the line. Every point in the equator is 90 degrees or a quadrant's distance from the poles; hence it divides the globe or sphere into two equal hemispheres, the northern and southern. At the meridian, the equator rises as much above the horizon as is the complement of the latitude of the place.