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Moon and Spica

July 22, 2015

The Moon cycles through its phases about once a month. It starts at new, waxes until it’s full, then wanes until it’s new once more.

Not only does it changes phases, but it also changes its position in the sky. It creeps into the western evening sky a couple of days after it’s new. When it’s full, it rises at sunset and remains visible all night. And a couple of days before it’s new again, it rises shortly before the Sun, so it’s in the eastern sky at first light.

If you lived on the side of the Moon that always faces Earth, you’d see our world going through the same cycle of phases that the Moon does. Unlike the Moon, though, Earth’s position in the sky wouldn’t change. Our planet would always appear in the same spot above the horizon, day and night, month after month.

Earth’s place in the sky would depend on your location on the lunar disk. If you were at the middle, Earth would stand straight overhead. But if you were near one of the poles, Earth would stand low above the horizon.

And if you lived on the lunar farside, you’d never see Earth at all — it would remain forever hidden on the other side of the Moon.

And the Moon itself isn’t hidden tonight. It’s near first quarter, so sunlight illuminates almost half of the lunar disk. It’s in the south as darkness falls, and sets a few hours later. Spica, the brightest star of Virgo, stands close to the left of the Moon — a bright companion to our always-on-the-move satellite world.

Script by Damond Benningfield, Copyright 2015

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