Thursday, 23 December 2010

Once in a Red Moon

It seems that the December 21 of 2010 was quite saturated with important events. A very total and spectacular lunar eclipse took place last Tuesday. A lunar eclipse as we all know occurs when the Earth comes directly between the Sun and the Moon. The Earth casts it's shadow on the moon and the full moon disappears from the night sky for a while. Well, not quite. This is what actually happens.







As you can see the moon is never completely in the Earth's shadow. Instead at the peak of a lunar eclipse, the moon appears blood red. All of you will have seen a sunset, at least in pictures. The sun appears red because it has to pass through much more of the atmosphere that when it is directly overhead. In this case the sun's light passes through a similar amount of atmosphere before it falls on the moon. Radiation of shorter wavelengths are scattered in the atmosphere leaving wavelengths we perceive as red to go through and fall on the lunar surface. This causes the moon to glow in a most enchanting red colour. Certainly one of the more beautiful celestial events.



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