Science behind a solar eclipse


It's a phenomenon that's been linked to a dragon, a black squirrel and Tiangiou, the magical dog of heaven.

Mythologies from across the globe have blamed them all for eating the sun.

In reality, solar eclipses, like the one that can be seen across parts of the Northern Hemisphere this month, are down to an amazing coincidence.

The moon and sun are at just the right distance away from the Earth that they appear to be of the same apparent size in the sky even though the sun is about 400 times larger than the moon.

But that's not the whole story. A total eclipse can only be seen in the narrow corridor known as the "path of totality" --- or the "inner umbral shadow." The area where the sun's rays are only partially obscured is called the "penumbra."

Solar eclipses are relatively common -- partial eclipses are visible somewhere on Earth most years -- but not necessarily in the same region. You might wait hundreds of years between two total eclipses at the same place.

"The eclipse at totality allows us to see the inner most regions of the sun's atmosphere even if it's only for a few minutes -- it's very hard to do otherwise," Massey said.

Ahead of last year's eclipse in the United States, NASA advised CNN readers: "Even at maximum eclipse, a sliver of sun peeking out from behind the moon can still cause pain and eye damage. Direct viewing should only be attempted with the aid of a safe solar filter."

NASA suggested some old tricks for viewing indirectly, like punching a hole in cardboard and projecting the light seeping through it onto a surface away from the Sun.