The Moon will cover up the Sun early tomorrow, briefly turning day to night. Unfortunately, though, it'll happen while it's already night here in the United States, so we'll miss out on the show.
The event is a total solar eclipse. It happens thanks to a coincidence in the way the solar system is laid out: Even though the Sun is about 400 times wider than the Moon, it's also about 400 times farther away. So when the geometry is just right, the Moon can just cover the solar disk.
As the Sun disappears, the air gets cooler, and the sky turns dark. The Sun's hot but thin outer atmosphere, the corona, forms delicate streamers of light around the Moon. And the first or last moment of sunlight can form a "diamond ring" -- a thin ring of light around the Moon, with a bright burst where sunlight streams through canyons or between mountains.
The Moon's orbit is tilted a little, so most months the Moon passes just above or below the Sun, and there's no eclipse. But two or more times a year, the Moon's orbit lines up just right, creating an eclipse. Many eclipses are partial, so the Moon appears to only nick the Sun. But this time it goes right across the heart of the Sun, creating a beautiful eclipse.
The total eclipse is visible along a thin path that runs through China and Russia, across the tip of northern Greenland, and just into Canada. The partial eclipse is visible across a much wider area, but it doesn't include the U.S.
Script by Damond Benningfield, Copyright 2008
For more skywatching tips, astronomy news, and much more, read StarDate magazine.