In a lunar eclipse, the Sun, Earth and Moon are directly aligned and the Moon swings into the cone of shadow cast by the Earth.

But the Moon does not become invisible, as there is still residual light that is deflected towards it by our atmosphere. Most of this refracted light is in the red part of the spectrum and as a result the Moon, seen from Earth, turns a coppery, orange or even brownish hue.

Lunar eclipses have long been associated with superstitions and signs of ill omen, especially in battle.

The defeat of the Persian king Darius III by Alexander the Great in the Battle of Gaugamela in 331 BC was foretold by soothsayers when the Moon turned blood-red a few days earlier.

And an eclipse is credited with saving the life of Christopher Columbus and his crew in 1504.

Stranded on the coast of Jamaica, the explorers were running out of food and faced with increasingly hostile local inhabitants who were refusing to provide them with any more supplies.

Columbus, looking at an astronomical almanac compiled by a German mathematician, realised that a total eclipse of the Moon would occur on February 29, 1504.

He called the native leaders and warned them if they did not cooperate, he would make the Moon disappear from the sky the following night.

The warning, of course, came true, prompting the terrified people to beg Columbus to restore the Moon -- which he did, in return for as much food as his men needed. He and the crew were rescued on June 29, 1504.

The Moon will be in total eclipse from 0301 GMT to 0351 GMT. This will be visible east of the Rocky Mountains in North America, as well as in all of Central and South America, West Africa and Western Europe. The zenith of totality is close to French Guiana.

It will be in partial eclipse from 0143 GMT to 0301 GMT, visible west of the Rockies and from the eastern Pacific, and from 0351 GMT to 0509 GMT, visible across the rest of Africa and Europe and much of South and West Asia.

Under a partial eclipse, Earth's shadow, or umbra, appears to take a "bite" out of the Moon.

The last total lunar eclipse took place on August 28 2007. The next will take place on December 21 2010.

A solar eclipse happens when the Moon swings between the Earth and the Sun.

+ Further details: (http://sunearth.gsfc.nasa.gov/eclipse/OH/OH2008.html); (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=38834); and (http://www.skyandtelescope.com/observing/highlights/15357796.html).

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