The Collaborative International Dictionary
Equator \E*qua"tor\, n. [L. aequator one who equalizes: cf. F.
(Geog.) 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.
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(Astron.) 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 Equator 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.