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Moon and Companions

February 1, 2013

The Moon and a couple of bright companions put in a good showing at dawn this weekend. And for the Moon, the show doesn’t end there — it continues for most of the morning.

As twilight begins to paint the sky tomorrow, the star Spica stands close to the right of the Moon, with the planet Saturn a bit farther to the upper left of the Moon. By Sunday, the Moon will have moved eastward in its orbit around Earth, so both Spica and Saturn will be to its right.

As the twilight waxes, Saturn and Spica will wane, eventually fading from view — hidden in the glare of the daytime sky. The Moon will fade as well, but unlike its companions, it won’t disappear — it’ll remain in view until it sets in late morning.

In fact, over the course of its month-long cycle of phases, the Moon spends just as much time in the daytime sky as in the nighttime sky.

The Moon commands the night because it’s thousands of times brighter than just about any other astronomical object. But in the daytime sky, it’s a pale second. The Sun is about 400,000 times brighter than the full Moon, and a million times brighter than tomorrow’s gibbous Moon. And the blue glow of the daytime sky itself is much brighter than the dark of the night sky, so the Moon doesn’t stand out.

Once you notice the Moon in the daytime sky, though, you’ll wonder why you didn’t see it before — moving wanly across the Sun’s domain.

Tomorrow: the night sky in the daytime sky.


Script by Damond Benningfield, Copyright 2012

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