Jack Dikian
December 2010
Lunar Eclipse (December 21st 2010)
The lunar eclipse tonight promises to be a spectacular show, weather permitting. It will be visible anywhere in Australia, and begin at sunset when the earth, the sun and the moon fall into perfect alignment.
This is rare because the moon is usually either above or below the plane of the earth's orbit. According to Professor Mike Dopita from the Australian National University's School of Astronomy, "The moon gets this sometimes quite blood red colour and it's quite an interesting sight to see although it is of no astronomical importance at all.", also, "… Sometimes it's a kind of a sunset yellowish colour, sometimes it looks quite red. It depends upon whether there's been volcanic activity.
However, as the Earth slips between the sun and moon, changing the tint of the lunar surface from white to [orange] to russet and back, you're seeing the effect Earth's atmosphere is having on the colour of sunlight passing through it. But the atmosphere is doing something else. It's in effect tagging the sun's rays with the chemical fingerprints of gases in the atmosphere.
Over the past two years, two teams of astronomers have been using this effect to figure out what Earth might look like as a distant, extra-solar planet orbiting another star. By analyzing the light reflected off the moon during a lunar eclipse – light that has passed through Earth's atmosphere – they have detected gases in the atmosphere that indicate the presence of organic life on the planet.
The techniques may be able to detect evidence of organic life imprinted in an extra-solar planet's atmosphere – at least for rocky, Earth-mass planets orbiting stars relatively close to the sun – using large Earthbound telescopes.
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