Monday, October 1, 2007

Natural N3

James Stevens
Year 11 De La Salle College

Lunar Eclipse

A lunar eclipse occurs whenever the Moon passes through some portion of the Earth's shadow. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, the Moon is always full near a lunar eclipse. The type and length of an eclipse depend upon the Moon's location relative to its orbital nodes. The Moon does not completely disappear as it passes through the shadow because of the refraction of sunlight by the Earth's atmosphere into the shadow cone; if the Earth had no atmosphere, the Moon would be completely dark during an eclipse. The red colouring arises because sunlight reaching the Moon must pass through a long and dense layer of the Earth's atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the small particles, and so by the time the light has passed through the atmosphere, the longer wavelengths dominate. This resulting light we perceive as red. This is the same effect that causes sunsets and sunrises to turn the sky a reddish colour; an alternative way of considering the problem is to realise that, as viewed from the Moon, the Sun would appear to be setting (or rising) behind the Earth. The 28 August 2007 lunar eclipse was the second of two lunar eclipses to occur in 2007. It is the "longest and deepest lunar eclipse to be seen in 7 years". The next lunar eclipse of a longer duration will be on June 15, 2011.

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