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Home | Total Solar Eclipse 22nd July 2009 | What is a total eclipse of the Sun?
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| What is a total eclipse of the Sun? |
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Eclipses are unique astronomical events, occurring when the Earth, Moon, and Sun are exactly aligned in space. A solar eclipse occurs when our Moon passes in front of the Sun, casting a shadow across a portion of the Earth's surface. From some vantage points on the Earth, the Moon will only seem to block a piece of the Sun, and the Moon's shadow will not be completely dark. This is called a partial eclipse. But when the alignment is just right, observers in a few lucky locations on the Earth will see the Moon appear to cover the entire disc of the Sun. The Moon's shadow will be completely black, and "darkness will come across the skies.'' This is called a total eclipse.
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| The size of the Moon's shadow that we see depends on the distances, and sizes, of both the Moon and the Sun. By the time the Moon's dark shadow reaches our planet during a total eclipse, it is only about 200-300 kilometers wide. As the Earth rotates on its axis, that dark shadow seems to sweep across our planet, creating a path of total darkness. Observers must be within that path, called the path of totality, at the right time, to see a total solar eclipse. Observers on either side of this path — almost 2,200 miles on either side — will see only the partial eclipse. |
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| The shadow cast by our Moon 384,400 kilometers away would be similar in size to the shadow of a marble on a tennis ball 2 meters away. On this scale, the Sun would be a sphere 7 meters (23 feet) in diameter almost 750 meters away. |
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