For those of you in the Americas who are normally up with the chickens, or those of you with insomnia, Tuesday morning is your chance to see a total eclipse of the moon. Starting at about 4:51am EDT (1:51am Pacific), the moon will begin to slip into the shadow of the Earth, and by 5:52am EDT (2:52 am Pacific), the moon will be totally eclipsed, and thus it will remain until 4:23am Pacific; a partial eclipse will last for about another hour. Those on the East Coast of the US will see the moon set while in total eclipse.
If you live in Hawaii, the eclipse will be visible around midnight on Monday night/Tuesday morning, and if you are in Australia, New Zealand, or far eastern Russia (I don't think I have many readers there, but just in case...), the eclipse will put on a nice show Tuesday night. Most of Asia, Africa, and Europe will miss the show :(
A lunar eclipse happens when the moon's orbit takes it into Earth's shadow. The picture above, a composite of pictures taken during the March 3rd, 2007 eclipse, shows the round shape of Earth's shadow nicely. Most orbits (most full moons), the moon passes just above or below Earth's shadow, and so there is no eclipse. But, once in a while, we get lucky.
During a total lunar eclipse, the moon turns a reddish color (sometimes dark red, sometimes almost black, sometimes a bright copper). This is because Earth's atmosphere bends some sunlight into what would otherwise be a dark shadow. In essence, the moon gets to see every sunset and every sunrise simultaneously! Some day, perhaps our astronauts will get to view the Earth surrounded by a bright ring of fire as they view a total eclipse of the sun by the Earth. But for now, we can only imagine.
Next March, those of us in the Americas will get to see yet another total eclipse of the moon (three in one year, which is rare!); the next total lunar eclipse will not be until December 2010. And it is only ten more years (Aug 21, 2017) until the continental USA gets its first total solar eclipse since 1979, a drought of 38 years.