equinox

equinox

either of the two occasions, six months apart, when day and night are of equal length

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Equinox

(religion, spiritualism, and occult)

The equinoxes (from the Latin for “equal night”) are the two points in the year when the length of the day is equal to that of the night. These are the vernal (spring) equinox, which occurs on the first day of spring (on or around March 21), and the autumnal equinox, which takes place on the first day of fall (on or around September 23). In astronomical terms, the equinoxes occur when Earth reaches a place in its orbit where, from our point of view, the Sun appears to be situated at the exact intersection of the celestial equator and the ecliptic. The vernal equinox is especially important for Western astrologers, who regard the Sun’s position against the backdrop of the stars at the spring equinox (the vernal point) as the place where the zodiac begins.

Sources:

Filbey, John, and Peter Filbey. The Astrologer’s Companion. Wellingborough, Northamptonshire, UK: Aquarian Press, 1986.

Tester, Jim. A History of Western Astrology. New York: Ballantine, 1987.

The Astrology Book, Second Edition © 2003 Visible Ink Press®. All rights reserved.

equinox

[′ē·kwə‚näks]

(astronomy)

Either of the two points of intersection of the ecliptic and the celestial equator, occupied by the sun when its declination is 0°. Also known as equinoctial point.

That instant when the sun occupies one of the equinoctial points.

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

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

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Equinox

 

the moment at which the sun’s center crosses the celestial equator in the course of the sun’s apparent annual path along the ecliptic. At the time of the equinox, the length of the day is almost equal to that of the night over the entire earth, except near the poles. The difference is a matter of only a few minutes and results from refraction and the great angular diameter of the sun.

The point at which the sun’s center crosses the equator as the sun travels from the southern hemisphere to the northern hemisphere is called the vernal equinox. The point at which the sun’s center crosses the equator as the sun travels in the opposite direction is the autumnal equinox. Since the time between two successive transits of the sun through the same equinox (the tropical year) is not the same as the length of the calendar year, the equinox changes each year relative to the start of the calendar day. In a common year the equinox begins 5 hours 48 minutes 46 seconds later than the preceding year, while in a leap year it begins 18 hours 11 minutes 14 seconds earlier. The equinox may therefore extend over two successive calendar days. At the present time (second half of the 20th century), the sun passes through the vernal equinox on Mar. 20 and 21 (start of astronomical spring in the northern hemisphere) and the autumnal equinox on Sept. 23 (start of astronomical autumn in the northern hemisphere). These dates are given in the New Style for the start of the day in Moscow time.

Hipparchus (second century B.C.) discovered that the equinoxes slowly shift along the ecliptic in the direction of the apparent annual path of the sun. This shift, owing to the precession of the earth’s axis of rotation, has a period of about 26,000 years. In 1737, J. Bradley found that the earth’s axis experiences nutation, as a consequence of which the equinoxes complete oscillatory motions with a period of 18.6 years relative to their mean positions as determined by their precessional motion. Changes in the celestial coordinates of the heavenly bodies are related to the changing positions of the equinoxes. Star catalogs give the positions of stars for given vernal equinoxes of different epochs.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.