Thursday, June 16, 2011

Lunar eclipse: science behind why Moon changes colour

A lunar eclipse is when the Earth casts its shadow over the moon. Often the moon turns brown in an eclipse but can become a reddish, coppery colour or orange. Thursday's eclipse sent the moon into a "blood red" colour.

The lunar face is usually tinged by light from the Sun that refracts as it passes through our atmosphere. But the intensity of the colour depends on the amount of ash and dust in the atmosphere. The Moon, a cold, rocky body about 2,160 miles in diameter has no light of its own but shines by sunlight reflected from its surface. It orbits Earth about once every 29 and a half days and as it circles the planet, its changing position, in respect to the Sun, causes our natural satellite to cycle through a series of phase. An eclipse of the Moon (or lunar eclipse) can only occur at Full Moon.

The phenomenon known as a “total lunar eclipse” occurs when the planet completely blocks the sun, causing the moon to darken and appear to change colour. But the moon does not become completely shaded because the Earth's atmosphere refracts, or bends, indirect sunlight toward it, which gives off a dim illumination. As indirect sunlight must travel through the Earth's atmosphere before reaching the moon, any clouds or dust in the atmosphere will block out some colours in the sunlight.

“The total phase of a lunar eclipse is so interesting and beautiful precisely because of the filtering and refracting effect of Earth's atmosphere,” a Nasa spokesman says. Astronomers say this causes the moon to seem to change colour, frequently in yellow, orange, or red shades. The exact colour varies depending on weather conditions. The specific phenomenon that occurred on Thursday was known as a "deep lunar eclipse". Scientists said the eclipse could be safely observed with the naked eye. The next total lunar eclipse will be on December 10. There will be partial solar eclipses on July 1 and November 25, but the next total solar eclipse will not take place until November 13, next year.

Stargazers across the globe have been treated to  lunar eclipse, the longest in more than a decade, which turned the moon a blood red colour. Stargazers with clear skies throughout Europe, Africa, Asia and Australia were treated to the visual treat, when the terrestrial shadow started to fall at 6.24pm BST and lifted just before midnight. The "totality", which is when the lunar face is completely covered, lasted 100 min. which scientists said was the longest since July 2000


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