Eclipses occur when the Moon blocks the Sun from our view on Earth. The Moon appears to 'eat' the Sun gradually over time, before covering it completely. Later, the Sun would reappear as the Moon moves away.

There are 3 cases of solar eclipses:

1) Total Eclipse

The Moon is nearly the same size as the Sun as the two line up. The Moon appears to cover the sun and the Sun's corona can be seen. The period of totality, or how long the Moon is obscured, depends on the closeness of the moon to the Earth. The closer the Moon, the longer the period of totality.

2) Annular Eclipse

This occurs when the Moon is far from the Earth. It causes the Moon to be not big enough to cover the disk of the Sun. Hence, 'a ring of fire' around the disk of the Moon can be seen.

3) Partial Eclipse

This kind of eclipse does not completely cover the sun, but it is the most common and can be seen over a large area. In this event, only a portion of the Sun is covered by the Moon.

Transits

This only happens to the planets Venus and Mercury as they are in closer orbits to the Sun, thus we can witness them moving across the sun's surface. At certain periods of time they appear to travel across the disc of the Sun. The transits of Mercury occur much more regularly than that of Venus, which occurs twice in a century. The latest to happen is going to be on 8th June 2004, the next won't happen till June 2012, before a break of about close to a century. 

Venus Transit 2004 as seen from Singapore

For more images and graphics on eclipses and transits, visit NASA's SunEarth web site on eclipses and transits

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