March equinox

March equinox

[′märch ′ē·kwə‚näks]

(astronomy)

vernal equinox

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

vernal equinox

i. That point of intersection of the ecliptic and the celestial equator occupied by the sun as it changes from a south to a north declination, on or about March 21. Also called the March equinox or the first point of Aries.
ii. That instant the sun reaches the point of zero declination when crossing the celestial equator from south to north.

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equinox

Positions of sun and the earth at spring and autumnal equinoxes.

i. One of the two points of intersection of the ecliptic and the celestial equators, occupied by the sun when its declination is 0°. Also called an equinoctial point. That point occupied on or about March 21, when the sun's declination changes from south to north, is called the vernal equinox, spring equinox, March equinox, or first point of Aries that point occupied on or about September 23, when the declination changes from north to south, is called the autumnal equinox, September equinox, or first point of Libra. Equinox is often used to mean vernal equinox, when referring to the origin of measurement of right ascension and celestial longitude. At the time of equinox, the duration of day and night is the same or equal.
ii. That instant the sun occupies one of the equinoctial points.

An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved