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Vernal Equinox


Can You Balance Eggs on End During the Spring Equinox?

March 20th is the first day of spring, or vernal equinox, as astronomers would have it. (The first day of spring used to be March 21st, but astronomers also say our winters are getting shorter.)  "Equinox" means, literally, "equal night."  As the tilt of the earth's axis changes throughout the year, lengthening or shortening the days according to season and hemisphere, there are two times annually when day and night are of equal duration: the spring and autumnal equinoxes.

This celestial phenomenon has been recognized for thousands of years and has given rise to a considerable body of seasonal folklore.

Eostra, Estrogen, Easter   Spring has been celebrated throughout human history as a time of organic and spiritual rebirth, following the "dying of the year" in winter.

The ancient Germanic festival of Ostara (in honor of the goddess also known as Eostra, from whose name the word estrogen was derived) celebrated the cyclical return of light and life with fertility rituals and symbols, some of which still survive in the modern observance of Easter (also derived from "Eostra"), which traditionally falls on the first Sunday after the first full moon following the spring equinox.

Eggs in the balance The egg being the most literal and obvious of all fertility symbols, ancient eggish customs survive not only in the form of Easter eggs, but also in the quaint superstitious belief, most often attributed to the Chinese, that you can stand a raw egg on end during the equinox. This apparently derives from the notion that, due to the sun's equidistant position between the poles of the earth on the first day of spring, special gravitational forces apply.

It can be done, by the way, but the trick takes lots of patience, eggs of just the right shape, a pinch of salt if all else fails... and, frankly, it doesn't matter what day of the year you attempt it.

The Bad Astronomy home page rightly condemns all this equinox-egg-balancing folderol as unscientific hooey, but don't let that stop you from gathering friends and family around to try it out yourself. At the risk of being boiled and dyed for heresy, I daresay there is more to life than science.


Egg balanced on end before the equinox
Author's photo of an egg successfully balanced on end.

From David Emery,


The date (near March 21 in the northern hemisphere) when night and day are nearly the same length and Sun crosses the celestial equator (i.e., declination 0) moving northward. In the southern hemisphere, the vernal equinox corresponds to the center of the Sun crossing the celestial equator moving southward and occurs on the date of the northern autumnal equinox. The vernal equinox marks the first day of the season of spring. The right ascension at the vernal equinox originally was in the constellation Aries and the point of crossing was known as the first point in Aries (now actually in Pisces because of precession Eric Weisstein's World of Physics).

The above plots show how the date of the vernal equinox shifts through the Gregorian calendar according to the insertion of leap years. The table below gives the universal time of the vernal equinox. To convert to U. S. Eastern standard time, subtract 5 hours, so the vernal equinox occurs on March 20, 2001 at 8:14 a.m. EST.

Note that the times below were calculated using VernalEquinox[] in the Mathematica application package Scientific Astronomer, which is accurate to within only an hour or so, and in practice gives times that differ by up to 15 minutes from those computed by the U.S. Naval Observatory (which computes March 21, 1999 at 01:46 UT instead of 01:36 UT and March 20, 2000 at 07:35 UT instead of 07:25).

Date UT Date UT Date UT
03-20-1980 11:05 03-20-1990 21:15 03-20-2000 07:25
03-20-1981 16:54 03-21-1991 03:04 03-20-2001 13:14
03-20-1982 22:43 03-20-1992 08:53 03-20-2002 19:03
03-21-1983 04:32 03-20-1993 14:42 03-21-2003 00:52
03-20-1984 10:21 03-20-1994 20:31 03-20-2004 06:41
03-20-1985 16:10 03-21-1995 02:20 03-20-2005 12:30
03-20-1986 21:59 03-20-1996 08:09 03-20-2006 18:19
03-21-1987 03:48 03-20-1997 13:58 03-21-2007 00:08
03-20-1988 09:37 03-20-1998 19:47 03-20-2008 05:57
03-20-1989 15:26 03-21-1999 01:36 03-20-2009 11:46

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