Dec. 20, 2010 -- For astronomy fans, Christmas comes early this week.
The eclipse will be visible Monday night on the West Coast and during the early hours Tuesday on the East Coast.
If the sky is clear, experts say the show might be extra spectacular, as the moon will have a reddish glow.
A lunar eclipse takes place when the sun, Earth and moon are all perfectly aligned with the Earth in the middle. When the moon passes behind the Earth, the sun's rays are blocked from striking the moon. This can only occur when the moon is full.
Lunar Eclipse to Last About Three and a Half Hours
As the moon moves deeper into Earth's shadow, indirect sunlight passes through Earth's atmosphere, casting an orange and red hue over the moon.
Unlike a solar eclipse, which can only be seen for a few moments from any specific spot, a lunar eclipse can be viewed for several hours. It is also safe to view a lunar eclipse without special glasses or equipment.
2011 to Have Two Lunar Eclipses
According to NASA, the total phase should last about three and a half hours when it begins as a partial eclipse at 1:33 a.m. ET and it will finish at 5:01 a.m. ET. The totality phase -- when the moon is entirely inside Earth's shadow -- will last approximately 72 minutes.
This year's only lunar eclipse actually coincides with the winter solstice, meaning that the moon will appear high in the night sky, aiding visibility for revelers.
There will be two total lunar eclipses in 2011 -- one in June and one in December. North America will miss the June show and witness only a part of next December's eclipse.
Find out more about the Dec. 21 lunar eclipse here at NASA's website.