E·qua·tor n.
 1. 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.
 2. 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.

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 E·qui·noc·tial a.
 1. Pertaining to an equinox, or the equinoxes, or to the time of equal day and night; as, the equinoctial line.
 2. Pertaining to the regions or climate of the equinoctial line or equator; in or near that line; as, equinoctial heat; an equinoctial sun.
 3. Pertaining to the time when the sun enters the equinoctial points; as, an equinoctial gale or storm, that is, one happening at or near the time of the equinox, in any part of the world.
 Equinoctial colure Astron., the meridian passing through the equinoctial points.
 Equinoctial line Astron., the celestial equator; -- so called because when the sun is on it, the nights and days are of equal length in all parts of the world. See Equator.
 Thrice the equinoctial line
 He circled.   --Milton.
 -- Equinoctial points Astron., the two points where the celestial and ecliptic intersect each other; the one being in the first point of Aries, the other in the first point of Libra.
 Equinoctial time Astron. reckoned in any year from the instant when the mean sun is at the mean vernal equinoctial point.


 equinoctial line
      n : the great circle on the celestial sphere midway between the
          celestial poles [syn: celestial equator, {equinoctial
          circle, equinoctial]