The moon will appear to take a bite out of the sun tomorrow during the first of four partial solar eclipses slated to happen in 2011. Sky-watchers across most of continental Europe, North Africa, the Middle East, and Central Asia will be able to see the celestial event.
Solar eclipses occur when Earth, the moon, and the sun are aligned so that—as seen from Earth—the moon appears to cover all or part of the sun's disk.
A given year may see up to three different kinds of solar eclipses. During a total eclipse, the moon completely blots out the sun, casting its dark central shadow, called the umbra, onto a very narrow strip along Earth's surface. (See pictures of the most recent total solar eclipse, over Easter Island.)
An annular eclipse happens when the moon covers only the central part of the sun's disk, leaving a ring of sunlight still visible. And partial solar eclipses happen when Earth crosses only through the faint outer part of the moon's shadow, known as the penumbra. (See annular eclipse pictures.)
On Tuesday the moon's silhouette will start to move across the sun at 6:40 a.m. UT, when the penumbra hits Algeria. The last traces of the moon's outer shadow will cross northwest China at 11 a.m. UT.
This year will be unusual, because there will be no total or annular eclipses, just partials, said eclipse expert Jay Pasachoff, the Field Memorial Professor of Astronomy at Williams College in Massachusetts.
"That hasn't happened since 1982 and won't happen again until 2029," said Pasachoff, who is also a National Geographic grantee. (The National Geographic Society owns National Geographic News.)
"Both total and annular eclipses each occur on average every 18 months, so usually one or the other occurs in a calendar year."
The next total solar eclipse won't happen until November 14, 2012, when the path of the moon's shadow crosses Australia and the South Pacific.
Eclipse to Create a Crescent Sunrise
The amount of the solar disk hidden by the moon during a partial eclipse depends on how far an observer is inside the penumbral shadow. (See pictures of last month's total lunar eclipse.)
For Tuesday's partial eclipse, many capital cities across Europe and the Middle East will see more than 50 percent of the sun eaten away by the moon.
"The farther north you are in Europe, the more of the sun you will see covered," said eclipse chaser and astronomer Alan Dyer of the Telus World of Science in Calgary, Canada.
At maximum eclipse—at 8:50 a.m. UT—the moon will blot out 85 percent of the sun, as seen from Scandinavian countries.
"But at this eclipse the moon's umbral shadow passes above the North Pole of our planet and misses Earth [by 317 miles, or 510 kilometers]," Dyer said, "so no place on Earth sees the sun totally eclipsed."
Still, in other parts of Europe, a partial eclipse so close to sunrise means that a crescent sun may greet sky-watchers at dawn.
And a sunset eclipse will be visible farther east, from central Russia to Mongolia. North America will not see any portion of Tuesday's eclipse.
Safety First When Viewing Eclipses
Observers should remember to take precautions not to damage their eyes when looking at the partially eclipsed sun, Williams College's Pasachoff said.
To safely look directly at the sun requires special filter-protected glasses or telescopes. But there are easy alternatives for observing an eclipse. For example, Pasachoff suggests making a simple pinhole camera.
"Just punch a hole a few millimeters across in a piece of cardboard and hold it up to sunlight, and look at the image that it casts with the sun at your back. You should easily be able to see the shape of the partially eclipsed sun."
And watching an eclipse, even a partial one, is an opportunity to witness the ongoing cycles of our solar system, Telus's Dyer added. (Also see "Ancient Eclipse Found in The Odyssey, Scientists Say.")
"Though we can predict eclipses with astonishing accuracy, they are created by forces far beyond our control," he said. "Eclipses remind us of our place in the universe."