equinoxes


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Related to equinoxes: precession of the equinoxes

equinoxes

1. (equinoctial points) The two points on the celestial sphere at which the ecliptic intersects the celestial equator. They are thus the two points at which the Sun in its apparent annual motion crosses the celestial equator. The Sun crosses from south to north of the equator at the dynamical equinox, still informally called the vernal equinox, symbol:, which lies at present in the constellation Pisces. The Sun crosses from north to south of the equator at the autumnal equinox, symbol: ≊, which at present lies in Virgo. The dynamical or vernal equinox is the zero point for both the equatorial and ecliptic coordinate systems, although in star catalogs a catalog equinox is now used. The equinoxes are not fixed in position but are moving westward around the ecliptic as a result of precession of the Earth's axis; the advance is about 50″ of arc per year. See also mean equator and equinox; true equator and equinox.
2. The two instants at which the Sun crosses the equinoctial points, on about March 21 (dynamical equinox) and Sept. 23. On the days of the equinoxes the hours of daylight and of darkness are equal.

Compare solstices.

References in periodicals archive ?
In this work, the same analysis is applied to the data including "planetary equinoxes".
The fact that the histogram shape variations do not depend on the nature of celestial body is confirmed also by pairwise comparison of the "equinoxes" of different planets.
However, in this particular case, symbate "equinoxes" (Venus 2001-October-18([down arrow]) and Moon-2005-March-25([down arrow])) happened to be less similar then the counter-directed ones (Venus-2001-October-18([down arrow]) and the other two Moon "equinoxes", both rising).
A question arose if there are a number of such "palindrome" centers existing at the equinoxes and "planetary equinoxes", separating the celestial body movement towards and away from the celestial equator.
In this series of data, the sequences of histograms obtained at the sequential (neighboring) "equinoxes" displayed higher similarity when they were compared as parallel sequences (procedure A in Fig.
The shape of histograms obtained from the measurements performed in different geographic locations near the time of "equinoxes" is changing synchronously, within one minute accuracy.
The changes of histograms obtained near the solar or planetary "equinoxes" do not depend on the nature of the "acting" celestial body, whatever the Sun, Mercury, Mars, Venus or Mercury.
By then, however, a cycle of four seasons linked with the Sun's progress on the ecliptic and bounded by the solstices and equinoxes was already well established in Mesopotamia.
Eudoxus of Cnidus, a Greek astronomer and scholar in the 4th century BC, followed Mesopotamian astronomical conventions and formalized the placement of solstices and equinoxes among the signs of the zodiac.
However, residents of the Eastern Hemisphere will see several March 21st equinoxes throughout the 21st century, (http://www.space.com/20279-spring-begins-early-2013.html) according to Space.com .