What is a Total Solar Eclipse?

To the naked eye, the sky is simply a bowl containing thousands of glowing dots and exactly two luminous disks. The points - stars and planets – have no size because of immense distance. The two disks are the Sun and the Moon.

Which is bigger? This is the amazing thing. The Sun and Moon appear the same size. That’s why the Moon can sometimes fit perfectly over the Sun, blocking it precisely so that we can see the normally invisible geysers of pink nuclear flame shooting up from its edges -- and its eerie glowing atmosphere. This is a total solar eclipse. None of these phenomena are visible during the much more common partial solar eclipse, when the Sun remains blindingly bright and the sky remains daytime-blue.

How Rare Is It?

The sun is 400 times larger, but also 400 times farther from us than the Moon. This fact alone allows the moon to fit perfectly over the sun's face. This bizarre coincidence does not hold for any other planet or moon, and indeed was not so here on Earth prior to the advent of us mammals, thanks to the moon's gradually increasing distance as it spirals away like a bent skyrocket.

The Moon does NOT pass in front of the Sun each time it swings around us in its 27 1/3 day orbit. That’s because of the moon's five-degree orbital tilt, which makes it miss the Sun almost every time it passes by. And even when it does block the sun, the moon's shadow, tapering like a chopstick to barely touch the ground, can be fully viewed from just a tiny section of Earth. If you're lucky enough to be in the right place at the right time, you experience a total solar eclipse, one of the greatest spectacles the eye can behold. From a much wider area it's merely a partial eclipse, a fairly common sight that requires eye protection.

You'd think a partial eclipse would be almost as impressive as totality. But it's not even close. The difference is day and night. This is why totality alone is so prized. Alas, the Moon casts its shadow along just a narrow ribbon of our planet. Even on the correct day of a total eclipse, if you’re not located within this 130-mile wide strip, you will not see totality; that’s why these events are so rare.

Why is Totality So Special?

A unique visceral presence develops when the sun, moon, and your spot on Earth form a perfectly straight line in space. Animals aren't alone in exhibiting aberrant behavior; a total eclipse makes many people shout and babble as if the event were an excursion by asylum inmates. It's estimated that about half of all observers make such primal, unsophisticated sounds.

Moreover, the experience ineffably surpasses the merely visual. Certainly it is beautiful, as the delicate otherworldly tendrils of the sun's corona, or atmosphere, splays into the surrounding sky. A solar totality, unlike a lunar eclipse, also offers the opportunity for rare science, since solar phenomena like prominences that are otherwise invisible, now gloriously appear.

A total solar eclipse happens somewhere on Earth on most years. But they’re very rare for any given location. Each spot of our world gets to see one only every 360 years, on average. And, hopefully, it won’t be cloudy that day!

SLOOH's Live Coverage

Totality can last between one second and seven minutes. The 2012 event in Australia will persist for two minutes and four seconds. This astonishing phenomenon follows an hour-long, steadily deepening partial solar eclipse, when the Sun is increasingly covered up, and undergoes a strange series of moonlike phases. SLOOH will cover this event right from the beginning.