Red moon of a lunar eclipse

Total lunar eclipse (Photo: Fred Espenak,

A break from solar eclipses, here’s a amazing picture of a lunae eclipse.

Unlike a total eclipse of the Sun, the Moon during a total lunar eclipse does not completely disappear as it passes through the umbra of the earth’s shadow. This is because of the refraction of sunlight by the Earth’s atmosphere into the cone of the shadow.

This renders the Moon a red colour because sunlight reaching the Moon first passes through the Earth’s atmosphere and becomes scattered.

The short wavelengths are more likely to be scattered by the atmosphere and the particles in it. As such, longer wavelengths (the reds) dominate and continue to pass through. The resulting light we perceive is thus red.

It’s the same effect that causes sunsets and sunrises to turn the sky red. (If we were on the Moon watching the Earth, the Sun would appear to be setting/rising behind the Earth.)

The next partial eclipse of the Moon will occur on December 31, 2009. To see the next total eclipse of the Moon, you will have to wait until December 21, 2010. In the meantime, there’s the chart below which projects its path and appearance.

21 Dec 2010 (Photo: SockPuppet for TomRuen


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One Response to “Red moon of a lunar eclipse”

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