Earth (Diameter: 12,756 km) moves around the Sun (Speed: about 30 km/sec) approximately once every 365 days. Moon (Diameter: 3,476 km) - which is about 385,000 km away from the Earth - moves around the Earth - approximately once every 29 days (Speed: about 1 km/sec).

These two motions - the motion of the Earth around the Sun and the motion of the Moon around the Earth - bring the Earth in between the Sun and the Moon - approximately once every 29 days. This is when we get the Full Moon (i.e half of the Moon receiving the Sun's light is visible from the Earth). Every year - there are 12 such occasions - once every lunar month.

Occasionally (at least twice a year) - the Earth comes just about exactly in between the Sun and the Moon. At such moments, the shadow of the Earth created by the Sun - would be falling on the Moon. This shadow would have two portions - the dark portion, Umbra and the light portion, Penumbra.

If the entire Moon happens to move within the Umbra region, we get a total lunar eclipse (whole of the Moon would be covered by Earth's shadow). If only a portion of the Moon moves within the Umbra region, we get a partial lunar eclipse (only a part of the Moon is covered by Earth's shadow). If the Moon moves within the Penumbra region, we get a penumbral lunar eclipse (hard to detect on most occasions).

There will be lunar eclipses on March 3, 2007 (Total), August 28, 2007 (Total), February 21, 2008 (Total), August 16, 2008, February 9, 2009 (Penumbral), July 7, 2009 (Penumbral), August 6, 2009 (Penumbral), December 31, 2009 (Partial), June 26, 2010 (Partial) and December 21, 2010 (Total). Depending on time of the day and the viewing location, these eclipses will be visible or not visible from Earth.