Equator

Part of speech: noun (n.)

1. The imaginary great circle on the earth's surface, everywhere equally distant from the two poles, and dividing the earth's surface into two hemispheres.

2. The great circle of the celestial sphere, coincident with the plane of the earth's equator; -- so called because when the sun is in it, the days and nights are of equal length; hence called also the equinoctial, and on maps, globes, etc., the equinoctial line. Equator of the sun or of a planet (Astron.), the great circle whose plane passes through through the center of the body, and is perpendicular to its axis of revolution. -- Magnetic equator. See Aclinic.