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Friday, January 15, 2010

A solar eclipse occurs when the moon passes in a direct line between the Earth and the sun. The moon's shadow travels over the Earth's surface and blocks out the sun's light. The moon orbits the Earth at approximately 5 degrees relative to the Earth-sun plane. The moon crosses the Earth's orbital plane only twice a year. These times are called eclipse seasons, because they are the only times when eclipses can happen. For an eclipse to take place, the moon must be in the correct phase during an eclipse season; for a solar eclipse, it must be a new moon. This condition makes solar eclipses rare.

The moon's shadow has two parts: a central region (umbra) and an outer region (penumbra). Depending upon which part of the shadow passes over you, you will see one of the three types of solar eclipses:

Total - The entire central portion of the sun is blocked out.
Partial - Only part of the sun's surface is blocked out.
Annular - Only a small, ring-like sliver of light is seen from the sun's disc.

If the umbra passes over you, the entire central portion of the sun will be blocked out. You will see a total solar eclipse, and the sky will darken like it were night time. During a total solar eclipse, you can see the sun's outer atmosphere, called the corona. In fact, this is the only time that you can see the corona.

If the penumbra passes over you, only part of the sun's surface will be blocked out. You will see a partial solar eclipse, and the sky may dim depending on how much of the sun's disc is covered.

Sometimes, the moon is far enough away in its orbit that the umbra never reaches the Earth at all. In this case, there is no region of totality, and what you see is an annular solar eclipse. In an annular eclipse, only a small, ring-like sliver of light is seen from the sun's disc.

How to Watch a Solar Eclipse

Never look at the sun directly. The best way to observe the sun is by projecting the image. Here is one way to project the sun's image:

Get two pieces of cardboard
With a pin or pencil point, poke a small hole in the center of one piece (no bigger than the pin or pencil point).
Take both pieces in your hand.
Stand with your back to the sun.
In one hand, hold the piece with the pinhole; place the other piece (the screen) behind it.
The sunlight will pass through the pinhole and form an image on the screen
Adjust the distance between the two pieces to focus and change the size of the image.

Total Eclipse

Partial Eclipse

Annular Eclipse

+ [ written by SEOWHWEE ] + 9:13 PM