vernal-equinox

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equinox

[ee-kwuh-noks, ek-wuh-]
noun
1.
the time when the sun crosses the plane of the earth's equator, making night and day of approximately equal length all over the earth and occurring about March 21 (vernal equinox or spring equinox) and September 22 (autumnal equinox)
2.
either of the equinoctial points.

Origin:
1350–1400; Middle English < Medieval Latin equinoxium, for Latin aequinoctium the time of equal days and nights (aequi- equi- + noct- (stem of nox) night + -ium -ium)

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World English Dictionary
equinox (ˈiːkwɪˌnɒks, ˈɛkwɪˌnɒks)
 
n
1.  vernal equinox See autumnal equinox either of the two occasions, six months apart, when day and night are of equal length
2.  another name for equinoctial point
 
[C14: from Medieval Latin equinoxium, changed from Latin aequinoctium, from aequi-equi- + nox night]

vernal equinox
 
n
1.  the time at which the sun crosses the plane of the equator towards the relevant hemisphere, making day and night of equal length. It occurs about March 21 in the N hemisphere (Sept 23 in the S hemisphere)
2.  a.  astronomy the point, lying in the constellation Pisces, at which the sun's ecliptic intersects the celestial equator
 b.  the time at which this occurs as the sun travels south to north (March 21)

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Etymonline
Word Origin & History

equinox
late 14c., from O.Fr. equinoxe, from M.L. equinoxium "equality of night (and day)," from L. aequinoctium, from aequus "equal" + nox (gen. noctis) "night." The O.E. translation was efnniht. Related: Equinoctial.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
equinox   (ē'kwə-nŏks')  Pronunciation Key 
  1. Either of the two points on the celestial sphere where the ecliptic (the apparent path of the Sun) crosses the celestial equator. ◇ The point at which the Sun's path crosses the celestial equator moving from south to north is called the vernal equinox. The vernal equinox marks the zero point in both the equatorial and ecliptic coordinate systems; horizontal angular distances (right ascension in the equatorial system and celestial longitude in the ecliptic system) are measured eastward from this point. The vernal equinox is also known as the first point of Aries because when first devised some 2,000 years ago this point occurred at the beginning of Aries in the zodiac. Because of the westward precession of the equinoxes, the vernal equinox is now located at the beginning of Pisces. ◇ The point at which the Sun's path crosses the celestial equator moving from north to south is called the autumnal equinox.

  2. Either of the two corresponding moments of the year when the Sun is directly above the Earth's equator. The vernal equinox occurs on March 20 or 21 and the autumnal equinox on September 22 or 23, marking the beginning of spring and autumn, respectively, in the Northern Hemisphere (and the reverse in the Southern Hemisphere). The days on which an equinox falls have about equal periods of sunlight and darkness. Compare solstice.


vernal equinox   (vûr'nəl)  Pronunciation Key 
See under equinox.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
equinox [(ee-kwuh-noks, ek-wuh-noks)]

The twice yearly times when the lengths of day and night are equal. At equinox, the sun is directly over the Earth's equator. The vernal equinox occurs about March 22 and the autumnal equinox about September 21.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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