SCIENCE -- December 20, 2010 at 1:58 PM ET
Calling all Night Owls and Moon Gazers: Total Lunar Eclipse in Tonight's Sky
During a total lunar eclipse, the moon has been known to turn dazzling colors: blood red, deep copper orange, and sometimes dark grey or brown.
For those of you tough enough to get out of your warm beds and into the winter solstice weather to turn your attention skyward, Tuesday morning's early hours mark the first total eclipse of the moon in two years. During this time, the moon will pass behind the earth, slip into the earth's shadow, become engulfed by that shadow, and then reemerge.
And if you happen to be in North America, Ireland or Greenland, you're perfectly positioned to see the moon pass through the northern part of the earth's shadow - weather and cloud-cover allowing, that is.
Here's how it works: The earth's shadow is cone-shaped and divided into two portions: the dark, inner umbra is nested inside the pale, outer penumbra. As the moon moves into the center of the umbra, it aligns with the sun and earth. There, hidden behind the earth, the moon is blocked from the sun's rays.
But a thin ring of atmosphere around the edge of the earth gets lit up by sunlight and refracted back onto the moon's surface. That's what causes the copper orange or red colors seen during an eclipse, says Jim O'Leary, senior director of the Maryland Science Center.
"We're never really sure what it's going to look like," he says. "It's really a function of whatever is going on in the atmosphere." Dust from volcanic eruptions, for example, can thicken the air and darken the color of an eclipse by canceling some of the light that gets reflected back onto the moon.
The eclipse will last three hours and 28 minutes. For 72 of those minutes, the earth's shadow will completely cover the moon, according to NASA.
Plus NASA plans to stream live video of the event and have astronomers available to answer questions online.
The moon will begin to enter the umbra at 1:32 am EST, at which point a visible dark shadow will start creeping across the moon's face. The total eclipse begins at 2:40 am, when the moon's final edge slips into the umbra. It will stay in the shadow until 3:53 am, and should be completed by 5:02 am. Meteorologist and astronomy writer Joe Rao details the 12 stages of the total lunar eclipse in this Space.com article.
The prime time to see the eclipse is 3:17 am EST, O'Leary says. "That's when the moon will be in deepest part of the shadow."
The last total eclipse visible from North America occurred three years ago. The next will occur in April 2014.