I was discussing lunar eclipses with my son this morning and a question came up that neither of us could explain to our satisfaction. During a total lunar eclipse, the full moon is still visible, but much dimmer than a non-eclipsed full moon. The explanation I've seen is that the eclipsed moon is lit by light reflected off of the Earth. The problem is that the earth is in a "new" phase, for the same reason that a solar eclipse only occurs during a new moon. I think that because the Earth has an atmosphere, there would be a ring of refracted light around the Earth and visible from the moon, but given the small albedo for the moon, that doesn't seem to be enough to explain the amount of light reflected from the moon. Any thoughts would be appreciated.

BTW, this question came up when my son was discussing lunar eclipses with one of his Science Olympiad teammates. His teammate asserted that the moon would be invisible, but my son told him that he had seen a total lunar eclipse and that the moon was very clear. This was a ready-made example of why experimental verification of theory is so important.

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I think you are right, light is bent around the earth, through the Earth's atmosphere. Some of this reaches the moon, even though the moon is in the center of the Earth's shadow.

That is why, sometimes an eclipsed moon will look reddish, especially if there has been a recent large volcanic eruption on earth that threw a lot of material into the upper atmosphere.

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The aldebo is low, and the light faint, but it is against a pitch black sky, so the contrast is strong.

Think of how bright the western sky is 5 minutes after sunset, when all the clouds turn red. It's still bright enough to walk around without streetlights. If you were on the Moon during totality, you'd be witnessing all of Earth's sunsets and sunrises at once.

And if the lunar eclipse is visible just before dawn, say, when the sky is a lot brighter, the moon is invisible. Very dramatic, as a bigger and bigger bite of the moon disappears.

During times of strong volcanic eruptions, when the atmosphere is saturated with volcanic dust, the fully eclipsed Moon is almost invisible, a phenomenon that I have experienced personally.

http://sunearth.gsfc.nasa.gov/eclips...E2004keen.html

Dave Mitsky

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