People in Europe, Africa or the Middle East, who had the best view of the last total lunar eclipse in March, won't see this one because the moon will have set when the eclipse begins at 4:51 a.m. EDT. It will take an hour to reach full eclipse stage.

An eclipse occurs when Earth passes between the sun and the moon, blocking the sun's light. It's rare because the moon is usually either above or below the plane of Earth's orbit.

Since the Earth is bigger than the moon, the process of the Earth's shadow taking a bigger and bigger "bite" out of the moon, totally eclipsing it before the shadow recedes, lasts about 3 1/2 hours, said Doug Duncan, director of the University of Colorado's Fiske Planetarium. The total eclipse phase, in which the moon has an orange or reddish glow, lasts about 1 1/2 hours.

The full eclipse will be visible across the United States, but East Coast viewers will only have about a half-hour to see it before the sun begins to rise and the moon sets. Skywatchers in the West will get the full show.

In eastern Asia, the moon will rise in various stages of eclipse.

During the full eclipse, the moon won't be completely dark because some light still reaches it around the edges of the Earth. The light is refracted as it passes through our atmosphere, scattering blue light -- which is why the sky is blue -- but sending reddish light onto the moon.

"When someone asks why is it (the moon) red, you can say because the sky is blue," Duncan said.

The next total lunar eclipse occurs Feb. 21, 2008, and will be visible from the Americas, Europe and Asia.