From Earth, a lunar eclipse occurs when Sun, Earth and Moon are in a single line with Earth in the middle. If this occurs, the Moon (or part of it) does not receive light from the Sun because it is in the shadow of the Earth, and thus the Moon becomes invisible even though there would normally have been a full moon. However, some of the light is refracted through the Earth's atmosphere to the Moon. Most blue light is scattered, and mainly red remains, and thus an eclipsed Moon will glow in reddish hues.
A penumbral eclipse occurs when the Moon passes through the Earth's penumbra only. In such a case the Moon still looks full but appears dimmer. A total lunar eclipse occurs when the Moon travels completely into the Earth's umbra. If only part of the Moon enters the umbra, then there is a partial lunar eclipse.
Lunar eclipses are only possible during a full moon, when the Moon is directly opposite the Sun. When it is full, the Moon usually passes above or below the ecliptic, which is why lunar eclipses are rare. However, on the occasions when it does align with the ecliptic, an eclipse will occur.
If you know the date and time of an eclipse, you can predict the occurrence of other eclipses using eclipse cycles.
Unlike a solar eclipse, which can only be viewed in a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth.
If you were on the Moon during a lunar eclipse you would witness a solar eclipse, with the Earth passing in front of the Sun.
The Moon's speed through the Earth's shadow is about 1km per second (3,600 km per hour) and the longest the Moon can remain completely within the Umbra is 102 minutess.
Expected Lunar Eclipses 2003-2005
| Date | Type | Where Visible | Expected Duration |
|---|---|---|---|
| 2003 November 9 | Total | Americas, Europe, Africa, central Asia | 24 min |
| 2004 May 4 | Total | South America, Europe, Africa, Asia, Australia | 1 hr 16 min |
| 2004 October 28 | Total | Americas, Europe, Africa, central Asia | 1 hr 21 min |
| 2005 April 24 | Penumbral | Americas, Australia, Pacific, Eastern Asia | Unknown |
| 2005 October 17 | Partial | Canada, Australia, Pacific, Asia | Unknown |
Ancient Greeks noticed that during lunar eclipses the edge of the shadow was always circular. They thus concluded that the Earth was spherical.
See also: eclipse, solar eclipseHistory of Lunar Eclipses