equinox


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Related to equinox: September equinox

equinox

(ē`kwĭnŏks), either of two points on the celestial spherecelestial sphere,
imaginary sphere of infinite radius with the earth at its center. It is used for describing the positions and motions of stars and other objects. For these purposes, any astronomical object can be thought of as being located at the point where the line of sight
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 where the eclipticecliptic
, the great circle on the celestial sphere that lies in the plane of the earth's orbit (called the plane of the ecliptic). Because of the earth's yearly revolution around the sun, the sun appears to move in an annual journey through the heavens with the ecliptic as its
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 and the celestial equator intersect. The vernal equinox, also known as "the first point of Aries," is the point at which the sun appears to cross the celestial equator from south to north. This occurs about Mar. 21, marking the beginning of spring in the Northern Hemisphere. At the autumnal equinox, about Sept. 23, the sun again appears to cross the celestial equator, this time from north to south; this marks the beginning of autumn in the Northern Hemisphere. On the date of either equinox, night and day are of equal length (12 hr each) in all parts of the world; the word equinox is often used to refer to either of these dates. The equinoxes are not fixed points on the celestial sphere but move westward along the ecliptic, passing through all the constellations of the zodiaczodiac
[Gr. zoion=animal], in astronomy, zone of the sky that includes about 8° on either side of the ecliptic. The apparent paths of the sun, the moon, and the major planets all fall within this zone.
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 in 26,000 years. This motion is called the precession of the equinoxesprecession of the equinoxes,
westward motion of the equinoxes along the ecliptic. This motion was first noted by Hipparchus c.120 B.C. The precession is due to the gravitational attraction of the moon and sun on the equatorial bulge of the earth, which causes the earth's axis to
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. The vernal equinox is a reference point in the equatorial coordinate systemequatorial coordinate system,
the most commonly used astronomical coordinate system for indicating the positions of stars or other celestial objects on the celestial sphere. The celestial sphere is an imaginary sphere with the observer at its center.
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.

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.

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.

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.

equinox

equinoxclick for a larger image
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.

equinox

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