If you step outside late tonight into early Tuesday morning, you may notice the moon looks like a luminous rotten orange. It's a total lunar eclipse that will be visible to everyone in North and Central America, including Alaska and Hawaii.
"We've all got a ringside seat to this one," says Alan MacRobert, editor of Sky & Telescope magazine. "We'll be watching it together."
During a lunar eclipse, the Earth lines up directly between the sun and the moon, so there is no direct sunlight to hit and reflect off the moon's surface. The only light that reaches it is "filtered and bending through our atmosphere," MacRobert says. That gives it the color of "all of the world's sunrises and sunsets" together.
The total eclipse will last for 72 minutes, a deeper "night within a night," as he puts it. The moon will be partially eclipsed for about an hour as it goes into and out of the Earth's shadow. The total eclipse will last from 2:41 to 3:53 a.m. ET.
"It's going to take a long time to watch the whole eclipse, about 3½ hours," says Rebecca Johnson, editor of StarDate magazine.
The color the moon takes on during the eclipse depends on what's in Earth's upper atmosphere, or stratosphere, says Fred Espenak, a scientist emeritus with NASA's Goddard Space Flight Center and eclipse specialist.
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"Volcanoes throw up sulfur dioxide, and when that gets to the upper atmosphere in the stratosphere, it combines with water vapor, creating a smog of sulfuric acid that reddens the light even more. So the more volcanic activity you have on Earth, the more it darkens and reddens the eclipse."
Richard Keen, an atmospheric scientist at the University of Colorado-Boulder, says the stratosphere is fairly clear right now, so this eclipse will be pretty light, most likely bright red to bright orange. "So it will be very colorful," Espenak says.
Most places on Earth see total lunar eclipses every three to five years. They tend to "occur in clumps," Espenak says.
There will be three over the next 12 months: Tonight, June 15 and Dec. 10. The June eclipse won't be visible from North America, and next December's will be visible only in the western part of the continent. "But the one coming up is ideally situated for all of the United States," he says.
In past ages, "these things spooked the bejesus out of people before people understood what caused them," MacRobert says.
VIEWER'S GUIDE: Total lunar eclipse
Today, science museums, parks, colleges and universities across the nation will be hosting viewing parties. Astronomers and telescopes will be on hand to explain what's happening and give the public a closer look into the awe-inspiring sight of the moon slowly disappearing from the sky.
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http://www.usatoday.com/tech/science/space/2010-12-20-Eclipse20_ST_N.htm
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