Sky-watchers' Guide: Lunar Eclipse Thursday
The full moon will get a tiny bite taken out of it tomorrow as it undergoes one of the shallowest and shortest partial eclipses of this century.
Here's what you need to know about the rare lunar event.
What is a lunar eclipse?
A lunar eclipse occurs when the sun, Earth, and moon align. During total lunar eclipses, the entire moon is engulfed in Earth's darkest shadow. But during partial eclipses, the moon never completely goes dark or turns red—only a portion of its disk appears to go dim.
"In this case, the moon only just clips the edge of the deepest part of the shadow, called the umbra," said Mark Hammergren, an astronomer at Adler Planetarium in Chicago, Illinois.
"The entire northern half of the moon will be slightly darkened by the penumbra, a broader, less intense area of the Earth's shadow."
A partial lunar eclipse is seen from Loudwater, England, in 2011.
Who will see it?
While North America will be left out of the sky show, much of the Eastern Hemisphere can see Earth's shadow brush across the outer half of the moon's surface over the course of the four-hour event.
All the stages of the eclipse will be visible across the Indian Ocean, central Asia, western Australia, Africa, and Europe.
Because only a tiny fraction of the moon's disk will dip into the darkest shadow cone, the entire partial eclipse phase will be a challenge to observe, lasting less than a half hour for viewers, Hammergren said.
"This eclipse is distinguished, or undistinguished, by being the second shortest partial eclipse of the moon in the 21st century, lasting only about 27 minutes," he said.
Luckily, armchair astronomers worldwide can watch the entire event from their computers via a public web feed.
SLOOH—an Internet-based space-tracking service—will be live streaming the eclipse with its robotic telescopes on the Canary Islands (map), broadcasting live over the Web starting at 3 p.m. ET on April 25.
When is best to watch?
The most readily visible part of the eclipse will begin at 3:54 p.m. ET, just as the moon is straight overhead for observers in the Indian Ocean.
The deepest and most interesting part of the eclipse—during which Earth's shadow will fall on less than 2 percent of the tiny sliver of the moon's disk—occurs at 4:07 p.m. ET and leaves the umbra at 4:21 p.m.
What if I miss this one?
Generally, between two and four lunar eclipses occur each year, but ones as slight as tomorrow's are rare.
The last time such a small partial lunar eclipse occurred was in 1958, and another one like it won't occur until 2034.
But don't fret: Later this year, two more partial lunar eclipses will be visible on May 25 and October 18.(Andrew Fazekas,National Geographic News,Published April 24, 2013)
