Christmas eclipse to provide holiday light show today

In a partial solar eclipse, the moon only covers part of the sun's disk, as in this September 2, 1997, eclipse

By Richard Stenger
CNN.com Writer

(CNN) -- Clear skies permitting, North Americans will receive a rare celestial gift today. A partial solar eclipse will be visible from nearly all regions of North America south of the Arctic Circle.

It won't happen again on Christmas Day for more than three centuries.

Sky watchers in different latitudes will see "bites" of various sizes removed from the sun as the moon passes in front of it, leaving a darkened shadow on the Earth.

About 72 percent of the sun's diameter will appear darkened from remote regions of northern Canada at the maximum phase of the eclipse, which comes at 12:35 p.m. EST, according to Sky & Telescope Magazine.

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The eclipse magnitude, or percent of the sun's diameter covered by the moon, will vary over the continental United States from more than 60 percent in the northeast to under 20 percent in the extreme southwest.

Viewers in parts of Central America and the Caribbean should be able to catch a glimpse of an even slighter eclipse.

The holiday light show takes place near the height of an 11-year cycle of sunspot activity on the sun. The moon could be seen in contact with some of the spots, according to Sky & Telescope.

Astronomers caution observers to never look directly at the sun, including during a solar eclipse.

"The eclipse itself if no more dangerous to view than the sun is on any other day," said NASA scientist Fred Espenak in a statement. "The only difference is that human curiosity impels some people to stare directly at the sun during an eclipse and this can cause permanent damage to your eyesight."

larger   Eclipse diagram (Copyright 2000 Sky Publishing Corp.)

Espenak advises eclipse watchers to use specially designed solar filters on optical devices or even a simple pinhole camera, which allows users to view a projected image of the sun.

Eclipses can only happen when a new moon passes between the sun and Earth. Observers can see the eclipse if the moon's shadow passes over them as it sweeps across the planet.

The last solar eclipse on December 25 occurred in 1954. It was an annular eclipse, in which case the moon darkens most of the sun but leaves a "ring of fire" around the edges.

The next total solar eclipse will darken parts of South America and Africa on June 21, 2001. Another Christmas Day solar eclipse, a partial one, won't happen until 2307.

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