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Moon and Companions

January 16, 2015

The Moon has a couple of bright companions at dawn tomorrow. Antares, the brightest star of Scorpius, stands to the right of the Moon. And slightly brighter Saturn, the second-largest planet in the solar system, is a little farther to the upper right of the Moon.

The Moon itself is a thin crescent right now. It’s about to pass between Earth and the Sun, so it’s daytime across most of the far side of the Moon, and nighttime across most of the near side.

If you were standing on the lunar nearside right now, its sky would be dominated by the bright gibbous Earth. Our planet is about to line up opposite the Sun as seen from the Moon, so it’s almost full.

And it would be an impressive sight. Earth is almost four times the Moon’s diameter, so it covers a much larger area than the Moon does as seen from Earth. Earth’s surface is much more reflective than the surface of the Moon, too; combined with its greater size, that makes a full Earth roughly 50 times brighter than a full Moon.

And since the same lunar hemisphere always faces our way, Earth stays in almost exactly the same spot in the sky as seen from any given location on the Moon, so you wouldn’t see Earth rise and set. You would see it go through an endless cycle of phases, though, from new to full and back to new. You’d also see our planet turn on its axis, and you’d see the patterns of clouds morphing from day to day — the ebb and flow of our constantly changing planet.


Script by Damond Benningfield, Copyright 2014

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