About the Spring Equinox

Overview, timing, & history

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Overview:

Religious followers from around the world observe many seasonal days of celebration during March and April. Most are religious holy days, and are linked in some way to the spring or vernal equinox. On that day, the daytime and nighttime hours are approximately equal -- each being 12 hours long.

Christianity and other religions associate three themes with the vernal equinox:

In the case of Christianity, the Apostle's Creed contains two of these themes. It states, in part, that Yeshua of Nazareth (a.k.a. Jesus Christ) was:

"... crucified, dead, and buried; he descended into hell; the third day he rose again from the dead;"

People view other religions in various ways, and thus treat the celebrations of other faiths differently:

When and why the vernal 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. The time of the year when the sun reaches its maximum elevation occurs on the day with the greatest number of daylight hours. This is called the summer solstice, and is typically JUN-21 -- the first day of summer. The lowest elevation occurs about DEC-21 and is the winter solstice -- the first day of winter, when the night time hours are maximum. Almost exactly half-way between the winter and summer solstice is the time of the vernal or spring equinox. It is one of two times during the year when the daytime and nighttime are almost exactly 12 hours long, and very close to being equal to each other. 

The date and time of the spring equinox:

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

Between the years 1503 CE and 2496 CE, the earliest spring equinox will be on 2496-MAR-19 at 12:28 UT. The latest was on 1503-MAR-21 at 8:42 UT.

The dates and times from 1999 to 2004 were derived from the astronomical calculations on The Dome of the Sky web site. ₂ The data for 2005 to 2010 was taken from archaeoastronomy.com ₃ An online "Easy Date Converter" calculates the dates and times of the equinoxes and solstices within 20 seconds. ₄ 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:

History of the spring equinox:

The early Romans used a lunar calendar in which months alternated between 29 and 30 days. It was not a precise measure; it gradually fell out of step with the seasons. Julius Caesar reformed the calendar by switching its base from lunar to solar. The day on which the vernal equinox occurred was defined as MAR-25. The length of the year was fixed at 365 days, with an additional leap-year day added every fourth year. This made the average length of a year equal to 365.25 days, which was fairly close to the actual value of 365.2422 days.

The annual error of 0.0078 days accumulated over time until it became unmanageable. A second reform of the calendar was ordered by Pope Gregory XIII. Under the new system, 1582-MAR-21 CE became the date of the vernal equinox, the year 1582 was shortened by ten days, and future centennial years (1600, 1700...2000) were not considered leap years unless they were divisible by 400. ₅ The Gregorian Calendar continues in general usage today. Eventually, its 0.0003 day annual error will accumulate and necessitate an elimination of a leap-year day circa 4915 CE.

References:

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

1. "Gwyl Canol Gwenwynol (Spring Eqinox) page," at: http://www.tylwythteg.com/Spring.html
2. "Find the equinoxes and solstices for a particular year," at  http://einstein.stcloudstate.edu/ 
3. "Equinox, Solstice & Cross-Quarter Moments," at: http://www.archaeoastronomy.com/
4. "Dates and Times of Equinoxes and Solstices," Hermetic Systems, at: http://www.hermetic.ch/
5. J.G. Walshe, et al., "Dates and meanings of religious and other festivals," Foulsham, (1997).

Copyright © 2000 to 2007 by Ontario Consultants on Religious Tolerance
Originally written: 2000-FEB-23
Latest update: 2007-MAR-27
Author: B.A. Robinson