Last Chance Until 2007: Total Lunar Eclipse

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Skywatchers on half the planet are gearing up to watch Earth's shadow consume a blood-red Moon tonight in the last total lunar eclipse until 2007.

Weather permitting, the easy-to-watch event will be visible across most of North and South America, Western Europe and Africa. It will be Web cast live from several locations, and glimpses might be televised during Game 4 of the World Series.

The eclipse begins at shortly after 8 p.m. ET (5 PT), but the first hour or so won't be noticeable as the Moon becomes lightly shaded by Earth's outer shadow, called the penumbra. Things get real interesting at 9:14 p.m. ET (6:14 PT), when the Moon begins sliding into Earth's full shadow, or umbra.

A dark and growing scallop will then gradually envelop Earth's only natural satellite. Once in total shadow at 10:23 p.m. ET (7:23 PT), the Moon might turn a shade of deep red that frightened the ancients. No two eclipses are alike, however, and astronomers can't say for sure what color to expect, if any.

What's going on:

Lunar eclipses occur when Earth's shadow prevents sunlight from reflecting off the Moon. They can only occur during full Moon, and only on the relatively rare occasions when the Moon's orbit carries it into the same plane of space as Earth's path around the Sun.

The schedule is predictable but somewhat erratic.

There have been four total lunar eclipses during the past 18 months, but there won't be another one until March 3, 2007.

During totality, when the Moon is completely immersed in shadow, it might turn red, the result of Earth's atmosphere bending hints of all the world's sunrises and sunsets simultaneously onto the Moon while the Sun's primary light is blocked.

Totality lasts until 11:45 p.m. ET (8:45 PT).

"The Moon will never be completely dark," explained Charles Schweighauser, professor of astronomy and physics at the University of Illinois at Springfield.

"The color of the Moon in shadow will range from a coppery color to dark red, depending on the amount of dust and water vapor in the Earth's atmosphere."

Easy to watch:

Telescopes are not needed to enjoy a lunar eclipse, but binoculars or a low-power telescope will enhance the color, astronomers advise. Otherwise, warm clothing and perhaps a lounge chair and a hot beverage are all that's needed to enjoy the show.

"Unlike solar eclipses, lunar eclipses are completely safe to watch," said Fred Espenak, a veteran eclipse forecaster at NASA.

People in parts of western Asia will glimpse a bit of the eclipse, and it will be visible from all of Canada and Central and South America. People in the western United States will miss the earliest stages, when the Moon is in the penumbral shadow of Earth.