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Professor Don Polacco explains the science behind the 'blood moon' phenomenon.

Commenting on the 'blood moon' phenomenon, Professor Don Pollacco from the University of Warwick Astronomy and Astrophysics Group, said: “The moon, like all planets, gives out no light of its own, but instead shines by reflecting sunlight. Tonight the moon during its monthly orbit of the Earth will pass through the earth’s shadow. During this period as sunlight can no longer reach the moon you might expect it to be invisible but instead a small amount of sunlight reaches the moon after passing through the Earths atmosphere and this light is then reflected off the lunar surface making it visible to us on Earth.

“As the sunlight travels through our atmosphere on its way to the moon the redder wavelengths pass through relatively unhindered while the bluer wavelength are scattered (thats why the sky is blue) by dust suspended in the earths atmosphere. The red light reaches the moon and is then reflected back to us. So the redness of the moon actually tells us about the conditions in our atmosphere.

“Consequently during a lunar eclipse the moon always appears red. Often the moon will turn a blood red colour and be very striking. Tonights eclipse (if we can see it at all because the weather forecast is not promising) is that the moon will rise in full eclipse. So just after sunset the moon will be visible low down in the eastern sky and already be a blood red colour. The full moon often looks larger when near the horizon (an illusion), so tonights eclipse could look impressive.”

27 July 2018


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