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Moon, Jupiter, and Spica

August 24, 2017

Fresh from its performance during Monday’s total eclipse, the Moon stages another beautiful encounter early this evening. It lines up with the planet Jupiter and the star Spica, the leading light of the constellation Virgo. Jupiter is by far the brighter of the two, with Spica close to its lower left. They’re quite low in the western sky at nightfall, and drop from view not long after.

During the eclipse, the Moon’s role was as a blackout curtain — it blocked the light from the Sun’s disk, allowing its wispy corona to shine through.

Tonight, though, the Moon itself takes center stage. It’s a thin crescent, with sunlight illuminating roughly one-eighth of the hemisphere that faces our way. As twilight begins to fade out, though, the rest of the lunar disk will become visible, too — illuminated by earthshine — sunlight reflected off of Earth.

And there’s a lot of it. As seen from the Moon, Earth would be in its gibbous phase this evening, with almost all of it in daylight. It would shine many times brighter than a full Moon, so the landscape would be plenty bright for an “earthlit” stroll.

Over the next few evenings, the Moon will stand higher in the sky at sunset, and it’ll be a fatter and fatter crescent. And the earthshine will begin to fade, because less of Earth’s daylight side will face the Moon. So the lunar night will get a little darker, under the light of a waning Earth.

More about the Moon and Jupiter tomorrow.


Script by Damond Benningfield

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