What's a Solar Eclipse?

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Hopefully, the latest installment of "The Twilight Saga" won't "eclipse" nature's phenomenon of the same name. While vampires and werewolves duke it out on the silver screen, some skywatchers will be able to catch a glimpse of a real solar eclipse coming up on July 11.

Eclipses are some of nature's most dramatic celestial performances. Solar eclipses occur when the Earth, moon and sun are aligned in the same plane and the moon passes between the Earth and the sun, partially or completely covering our closest star.

On July 11, the second solar eclipse of 2010 will occur, creating a total eclipse along a narrow corridor of the Earth's southern hemisphere.

A total solar eclipse typically only lasts for a few minutes, explained NASA solar astronomer Mitzi Adams of the Marshall Space Flight Center in Huntsville, Ala. The longest solar eclipse lasted about seven minutes, she said in a recent NASA webchat.

The first solar eclipse of the year was on Jan. 15, and was an annular solar eclipse, a term given to eclipses in which the moon covers a large portion (but not all) of the sun. It was visible for over eight minutes in some parts of Asia, but was not a total eclipse.

At least two, and sometimes up to five, solar eclipses can occur in a given year. But no more than two of those can be total eclipses.

Total eclipses are seen rarely because totality – when the sun appears totally hidden by the moon – only exists along a narrow path on Earth's surface, as opposed to partial eclipses which can be viewed across a much wider region.

The totality of the July 11 solar eclipse will be visible over a narrow swath of land extending through the southern Pacific Ocean and southern areas of Argentina and Chile in South America.

But when viewing a solar eclipse, looking at one through a telescope can be dangerous, Adams warned.

"You have to have a proper filter," she said. "The safest way is through a method called projection, where you actually take the eyepiece out and project the image onto a sheet of paper behind the telescope, without looking at the sun. You move the sheet of paper back and forth until you get a focused image."

It is safe to observe a solar eclipse with the naked eye, but only during the stage of complete totality, Adams said. Otherwise, looking at an eclipse is extremely dangerous. Special eye protection is needed to view the sun during partial and annular eclipses.

Regular sunglasses do not make viewing the sun safe, said Adams, as they do not adequately block enough of the infrared and ultraviolet radiation. Instead, only specially-designed "eclipse glasses" that use appropriate filtration should be used for direct viewing in these cases.

So, if you're in the right location on July 11, the sky will darken and you could see a spectacular show, all without having to set foot in a theater.

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