The Fall equinox

When and why does it happen?

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When and why the fall equinox happens:

The seasons of the year are caused by the 23.5º tilt of the earth's axis. Because the earth is rotating like a top or gyroscope, it points in a fixed direction continuously -- towards a point in space near the North Star. But the earth is also revolving around the sun. During half of the year, the southern hemisphere is more exposed to the sun than is the northern hemisphere. During the rest of the year, the reverse is true. At noontime in the Northern Hemisphere the sun appears high in the sky during summertime and low in the sky during winter. It is highest at the summer solstice (about June-21) and lowest at the winter solstice (about December-21).  The half-way points in the year are called the equinoxes. It is time of the year when the sun rises exactly in the east, travels through the sky for 12 hours, and sets exactly in the west. _1,2 Everywhere on earth experiences close to 12 hours of daylight, and 12 hours of nighttime.

The date and time of the fall equinox:

The exact date and time of the fall equinox, when the sun moves into the astrological sign of Libra, varies from year to year. Each year, the date/time moves progressively later in September until the year before leap-year is reached. On leap-year, it returns to an earlier date/time. This four-year cycle is then repeated. 

The dates and times were derived from the astronomical calculations on The Dome of the Sky web site for years 1999 to 2006. ₃ However, the web site now appears to be offline. The remaining equinoxes were taken from archaeoastronomy.com. ₄ An online "Easy Date Converter" calculates the dates and times of the equinoxes and solstices within 20 seconds. ₅ Times are in UT (Universal Time). This used to be called Greenwich Mean Time or GMT. In North America, you can find your local time by subtracting:

	2 hours 30 minutes for Newfoundland daylight savings time
	3 hours for ADT
	4 hours for EDT
	5 hours for CDT
	6 hours for MDT
	7 hours for PDT
	8 hours in AKDT (Alaska)
	9 hours in ADT (Aleutian Islands)
	10 hours in HST (Hawaii) 6

References used:

The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.

1. "The Sun in the sky during the Spring and Fall Equinox in the Northern hemisphere," at: http://solar.physics.montana.edu/
2. Jay Ryan, "Starman: Fall Equinox," at: http://www.oarval.org/
3. "Find the equinoxes and solstices for a particular year," at  http://einstein.stcloudstate.edu/
4. "Equinox, Solstice & Cross-Quarter Moments," at: http://www.archaeoastronomy.com/
5. "Dates and Times of Equinoxes and Solstices," Hermetic Systems, at: http://www.hermetic.ch/
6. Yisrayl Hawkins,"Ancient Pagan Religious Expression," at:  http://yahweh.com/

Copyright © 2002 to 2009 by Ontario Consultants on Religious Tolerance
Originally written: 2002-AUG-7
Latest update: 2009-SEP-21
Author: B.A. Robinson

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