Autumnal Equinox (redirected from Autumn equinox)

autumnal equinox [ȯ′təm·nəl ′ē·kwə‚näks]

(astronomy)

The point on the celestial sphere at which the sun's rays at noon are 90° above the horizon at the Equator, or at an angle of 90° with the earth's axis, and neither North nor South Pole is inclined to the sun; occurs in the Northern Hemisphere on approximately September 23 and marks the beginning of autumn. Also known as first point of Libra.

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Autumnal Equinox

September 22-23

The sun crosses the plane of the earth's equator twice a year: on or about March 21 ( see Vernal Equinox) and again six months later, on or about September 22 or 23. On these two occasions, night and day are of equal length all over the world. In the Northern Hemisphere, September 22 or 23 is the first day of autumn.
Autumnal Equinox Day is a national holiday in Japan, observed on either September 23 or 24 to celebrate the arrival of autumn and to honor family ancestors.
See also Higan; Shunbun-no-Hi

CONTACTS:
Lab for Particles and Fields
Code 672, Goddard Space Flight Center
Greenbelt, MD 20771
301-286-0447
www-istp.gsfc.nasa.gov
The Royal Observatory Greenwich
The National Maritime Museum Greenwich
London, SE10 9NF United Kingdom
44-20-8312-6565; fax: 44-20-8312-6632
www.rog.nmm.ac.uk

SOURCES:
AmerBkDays-2000, p. 665
BkDays-1864, vol. II, p. 364
DictDays-1988, p. 37
FolkWrldHol-1999, p. 565

Celebration days: Sep 22; Sep 23

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Autumnal Equinox 

one of the two times of the year when the sun crosses the celestial equator; occurs on Sept. 23. The autumnal equinox (astronomical symbol ≏) is that point of intersection of the ecliptic and the celestial equator at which the sun crosses the equator from north to south in its apparent annual motion on the celestial sphere.