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Moon and Jupiter

December 24, 2012

Long before the last blush of twilight fades away on this Christmas Eve night, two brilliant objects blaze into view in the east: the gibbous Moon and, to its lower left, the planet Jupiter. They arc high across the south during the night, drawing ever closer to each other as they do so.

Although they’re the two brightest objects in the sky for most of the night, neither the Moon nor Jupiter actually shines on its own — they don’t produce light like the bulbs on a Christmas tree. Instead, they shine by reflecting sunlight.

The Moon reflects very little sunlight — only about 10 percent, give or take. That means its surface is quite dark. But it’s so close to Earth that it forms a big disk in our sky, so there’s a lot of visible surface to reflect sunlight our way.

Jupiter is close to 2,000 times farther than the Moon, so it forms a much smaller target. But it’s the largest planet in the solar system, and it’s topped by bright clouds that reflect close to half of the sunlight that strikes them. So Jupiter shines brilliantly — only the Moon and the planet Venus are brighter.

One other bright object stands to the lower right of Jupiter: Aldebaran, the orange “eye” of Taurus. Although it looks fainter than Jupiter, that’s only because it’s farther away. Aldebaran is a giant star — one that’s much bigger and brighter than the Sun. But its light is dimmed by its great distance: more than 65 light-years.

More about this bright lineup tomorrow.


Script by Damond Benningfield, Copyright 2012

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