The Vernal Equinox

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— This year, spring officially arrives in the northern hemisphere at the moment of the vernal equinox -- about 11:26 a.m. March 20. Our spring begins the instant that the sun crosses the Earth's equator on its way north. With each passing day, the sun rises a little bit earlier and sets a little bit later, increasing the number of daylight hours for us to enjoy. The number of daylight hours will continue to increase until the summer solstice June 21 -- the longest day of the year and the first official day of summer.

Thanks to the 23 1/2-degree tilt of the Earth on its axis, the sun spends half the year shining straight down on the northern hemisphere and the other half shining straight down on the southern hemisphere. Separating these extremes are two days called the equinoxes --ix months apart -- when the sun shines straight down on the equator.

Equinox means "equal night" and is used to describe the two special days when every location on Earth experiences exactly 12 hours of daylight and 12 hours of darkness and the sun rises exactly in the east and sets exactly in the west. This year's autumnal equinox is at 9:03 p.m. Sept. 22, when the sun again crosses the equator, this time heading south.

Equinoxes always have been celebrated by various cultures. The ancient Druids went to great pains to align gigantic stones at Stonehenge so that they would point out the position of the rising sun on the dates of the equinoxes. The Great Sphinx of Egypt faces the direction of the rising sun on the day of the equinox. A coincidence? Probably not. For Christians, the celebration of Easter is tied directly to the vernal equinox: Easter Sunday is the Sunday that falls immediately after the first full moon after the equinox.

Oh, and that business about balancing an egg on its end only on the day of the equinox? It's a myth. You can just as easily balance an egg on its end any day of the year. Balancing an egg on its end has nothing to do with the balance of cosmic forces on the date of the equinox. Rather, it has to do with the tiny bumps on the eggshell that serve as little feet that the egg rests on. Be a myth-buster and try to balance that egg on a day that does'nt happen to be an equinox.

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