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Moon and Spica

April 4, 2015

The just-past-full Moon has a bright companion tonight: Spica, the brightest star of Virgo. It’s quite close to the lower right of the Moon at nightfall, and stays close as they arc low across the southern sky during the night.

If you take time to look at the Moon, you’ll notice random dark markings across its surface. They reminded long-ago astronomers of bodies of water, so they gave these features names like the Sea of Crises, the Sea of Tranquility, and the Ocean of Storms.

Those features aren’t bodies of water, though — they’re volcanic plains. They were created billions of years ago, when giant asteroids slammed into the Moon. The impacts formed wide, deep basins that filled with molten rock from below the lunar crust.

Yet they’re not completely dry. In fact, there’s quite a bit of water on the Moon — all in the form of ice.

Spacecraft have discovered large deposits of ice inside craters at the lunar poles. The bottoms of these craters never see the Sun’s rays, so they stay cold enough to hang onto the ice.

And samples returned by Apollo astronauts, as well as observations by automated spacecraft, have shown that tiny grains of ice are mixed with the lunar “dirt” across much of surface.

If we ever build colonies on the Moon, the water could be put to good use — providing not just drinking water, but oxygen for breathing, and oxygen and hydrogen for rocket fuel — precious resources from our not-quite-dry satellite world.


Script by Damond Benningfield, Copyright 2015

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