Image: Annular eclipse
Crack Palinggi  /  Reuters
The moon passes between the sun and the earth during an annular solar eclipse as seen from Indonesia on Jan. 26, 2009. This month's annular eclipse could provide a similar view.
By Starry Night Education
updated 1/14/2010 5:16:05 AM ET 2010-01-14T10:16:05

An annular solar eclipse, the "poor cousin" of a total eclipse of the sun, takes place on Friday.

The solar eclipse path begins in central Africa, crosses the Indian Ocean to touch the southern tip on India, and then moves on to southeast Asia, ending in southeastern China.

A partial solar eclipse will be visible over much of Africa and Asia.

An annular eclipse occurs when the Earth is closest to the sun at the same time as the moon is farthest from the Earth, so the moon isn't quite large enough to totally cover the disk of the sun. As a result, even at maximum eclipse, a ring of the sun appears behind the moon — hence the name "annular."

Although not as spectacular as a total solar eclipse, an annular eclipse is still an interesting event. Many of the events of a total eclipse are present, including the dimming of the sun's light and the effects on wildlife.

It is perhaps more dangerous than a total eclipse because the sun is never completely covered, so there is no time during the eclipse when it can be safely viewed without a dense filter. If a special solar eclipse filter is not available, a No. 14 welder's glass can be used. Note that this is denser than the standard No. 12 welder's glass, and can only be purchased in specialized welding shops.

One good way to view an eclipse safely is by placing a small mirror, less than an inch in diameter, on a sunny window ledge. This will project an image of the eclipsed sun into the room. The ground under a tree becomes a myriad of miniature eclipse images, as the eclipsed sun peeks between the leaves.

Computer software like Starry Night allows stay-at-home eclipse viewers to travel to any place along the eclipse path. As an example, we could virtually travel to Kampala, capital city of the landlocked African country of Uganda.

Kampala, like Rome, is a beautiful city built on seven hills. It is the home of Makerere University, the oldest university in East Africa. When the sun rises at 6:55 a.m. local time Friday, the eclipse is just about to begin. At 7:06, the moon starts to cover the upper limb of the sun. At 8:25, the moon is centrally placed on the sun, and the full annular effect is visible.

This would be a good time to try to spot Venus. Less than one degree from the eclipsed sun, Venus is extremely bright. Use a roof edge to block the sun, and see if you can spot Venus. By 10:04, the eclipse is over in Kampala.

At the other end of the eclipse track, in Chongqing, China, the eclipse begins at 2:22 p.m. local time with the moon approaching from the lower right, and reaches maximum at 3:51 p.m. Venus will be to the left of the eclipsed sun. The eclipse ends at 5:07 p.m., with the sun setting 10 minutes later.

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