I presume that I don't have to mention that there's a full lunar eclipse
tomorrow (Thursday) evening that will be visible from all of North America --
and that you all already have your lawn chairs out on the front lawn well
positioned for the event.

Nevertheless, for more information on the eclipse, see:

  http://skyandtelescope.com/observing/objects/eclipses/article_923_1.asp

If you were an astronaut anywhere on the front side of the moon tomorrow
night, the sun would be completely obscured by the velvety black disc of the
earth, with only the bright white tendrils of the sun's corona extending out
away from the earth's disc.

However, from the earth's point of view, looking back at the moon, the moon
won't go completely black. It will instead only become a deep blood red.
Nonetheless, as always it will be a truly impressive sight.

The reason that the moon doesn't go completely black is that the portion of
sunlight that grazes the earth and passes through the earth's very thin
atmosphere is refracted (bent) around the earth so that it strikes the moon
before bouncing back to earth as the light that you see. The light that
travels this path is preferentially made very red by the differential
absorption of the green and blue light by the dust in earth's atmosphere,
which is of course the same reason that the sun becomes reddened as it
approaches the horizon every evening.

Wirt Atmar

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