Vernal Equinox 2009: First Day of Spring

Friday, March 20, 2009

Vernal Equinox 2009: First Day of Spring

Vernal Equinox 2009: First Day of Spring
The vernal equinox occurs when the center of the sun crosses the Equator.

People raise their hands, some holding torches, to catch the first sunlight at the Teotihuacán Archaeological Site in Mexico City on the vernal equinox (or spring equinox) in 2004. The vernal equinox in 2009 falls on Friday, March 20.

Photograph: by Jaime Puebla/AP

In the Northern Hemisphere spring officially begins at 4:44 a.m. PT on Friday, March 20, 2009—the vernal equinox, or spring equinox

But don't be fooled by the old rumor that on the vernal equinox the length of day is exactly equal to the length of night.

The true days of day-night equality always fall before the vernal equinox and after the autumnal, or fall, equinox, according to Geoff Chester, a public affairs specialist with the U.S. Naval Observatory in Washington, D.C.

"Exactly when it happens depends on where you are located on the surface of the Earth," he said.

By the time the center of the sun passes over the Equator—the official definition of equinox—the day will be slightly longer than the night everywhere on Earth. The difference is a matter of geometry, atmosphere, and language.

Vernal Equinox Special Nonetheless

The length of day and night may not be equal on the vernal equinox, but that doesn't make the first day of spring any less special.

The fall and spring equinoxes, for starters, are the only two times during the year when the sun rises due east and sets due west, according to Alan MacRobert, a senior editor with Sky & Telescope magazine.

The equinoxes are also the only days of the year when a person standing on the Equator can see the sun passing directly overhead.

On the Northern Hemisphere's vernal equinox day, a person at the North Pole would see the sun skimming across the horizon, beginning six months of uninterrupted daylight.

A person at the South Pole would also see the sun skim the horizon, but it would signal the start of six months of darkness.

Info Source: nationalgeographic.com - Link

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Friday, March 20, 2009