E-quā'tor, n.

n. [It. equatore, Fr. équateur, Sp. ecuador, from Lat. æquare, æquatum. See EQUANT.]

1. (Geog.) A great circle on the earth’s surface, every where equally distant from the two poles, and dividing the earth’s surface into two hemispheres.
2. (Astron.) A 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 when drawn on maps, globes, &c., the equinoctial line, or simply the line.

Equator of the sun or a planet (Astron.), a great circle whose plane passes through the center of the body, and is perpendicular to its axis of revolution.