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Moon and Company

January 11, 2010

The Moon has some prominent companions in the eastern dawn sky tomorrow: the planet Mercury and the star Antares. Antares is to the upper right of the Moon and fairly easy to find. Mercury is about the same distance to the lower left of the Moon, and quite low in the sky. Although it looks like a bright star, you might need binoculars to pluck it from dawn's early light.

If you were standing on the Moon and looking back at Earth, you'd see quite a spectacle.

Earth is in its gibbous phase as seen from the Moon right now, so sunlight illuminates most of the hemisphere that faces the Moon. Earth is also bigger than the Moon -- it covers an area that's about 13 times greater than the Moon covers in our sky. And each square foot of Earth reflects several times more sunlight back into space than the Moon does.

So when you add it all up, it means that right now, Earth looks a couple of dozen times brighter than the full Moon. And that doesn't even cover what you'd actually see: continents and oceans, with clouds forming ever-changing patterns above them.

From Mercury, Earth would still be an impressive sight. It would be about as bright as the brightest stars and planets in our own night sky. And it would be the bluest object in the whole sky.

The view from Antares, though, would be nonexistent. Earth is so tiny, and so far away, that not even the biggest Earth-based telescopes could see our small, fragile world.

Script by Damond Benningfield, Copyright 2009

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