Lunar Eclipse in "Prime Time" on Wednesday
for National Geographic News
|February 18, 2008|
The Hollywood writers' strike may be over, but perhaps the best prime-time show in the Americas this Wednesday night will be in the sky: a total lunar eclipse.
The moon will be completely submerged in Earth's shadow from 10:01 to 10:51 p.m. ET.
"It's very well placed for the U.S.," said Fred Espenak, an astrophysicist and eclipse expert at the NASA Goddard Space Flight Center in Greenbelt, Maryland.
The celestial spectacle is visible throughout the Americas as well as during the wee hours of Thursday morning in Europe, most of Africa, and western Asia.
All told, well over a billion people will have the opportunity to view the show, according to Espenak.
A total lunar eclipse occurs when the sun, Earth, and moon form a nearly straight line in space. The alignment causes the full moon to pass through Earth's shadow.
The moon doesnt completely disappear, because some sunlight scatters around the edge of Earth's atmosphere and reaches the moon.
"It usually glows as an eerie, coppery red disk in the sky," Sky and Telescope magazine explained in a media statement.
(See a photo of the March 3, 2007, lunar eclipse.)
According to NASA's Espenak, however, the moon's appearance can vary during an eclipse, depending on atmospheric conditions.
A major factor is Earth's cloud cover, especially the extent of cover where sunrise and sunset are occurring during the eclipse.
"That's where sunlight is filtering through the Earth's atmosphere and being refracted into the moon's direction to illuminate the moon," he said.
For example, cloudy weather where the sun is setting will block more light from reaching the moon, thus making the moon appear darker.
And since Earth is moving during the eclipse, the sun's position behind Earth changes, making the light bending around the edges change in brightness as well.
In addition, dust in Earth's atmosphere, such as from recent volcanic activity, can dim the moon's brightness.
No major eruptions have occurred recently, however, so dust shouldn't be a factor Wednesday, Espenak noted.
Wednesday's eclipse officially gets underway at 8:43 p.m. ET, when the moon's eastern edge slips into Earth's shadow.
The 50-minute totality begins at 10:01 p.m. The eclipse ends at 12:09 am Thursday.
Up to three total lunar eclipses occur a year, but some years have none. The next one won't occur until December 21, 2010.
Local weather depending, Espenak encourages eclipse enthusiasts to take advantage of Wednesday's event, especially given the relatively convenient viewing hours in the Americas.
"Even though there might be a chance to see one every two, three, or four years, a good percentage of those are clouded out, so you don't get to see them," he said.
Unfortunately, in Seattle, where this writer lives, Wednesday's forecast is for clouds and rain likely.
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