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Sail Away On The First Quarter Moon

17 Aug 2018, 23:28 UTC
Sail Away On The First Quarter Moon
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Tonight’s first quarter moon shows off its dark spots called seas or “maria” tonight. How many can you see with your naked eye? Binoculars? Bob King
They looked like seas to ancient skywatchers, but looks can deceive. Those gray patches that kids assemble into the face of the man on the moon appear smooth and dark from Earth, the way a large body of water might look when see from orbit. With the advent of the telescope in the early 1600s astronomers quickly realized that they were relatively craterless lunar plains.
Look for the moon tonight in the southwestern sky between Jupiter and Antares. Stellarium
Now, we know that the seas (“maria” — MAH-ree-uh — in Latin) began as giant scars left by asteroid impacts around 3.9 billion years ago, when the moon was just a babe. Between 3.5 and 3 billion years ago they filled with dark basaltic magma that bubbled up from deep within the moon’s interior. Because most of the heavy meteoroid bombardment by meteoroids had occurred millions of years earlier, the seas generally lack big craters, giving them a smooth appearance. Closer inspection with a telescope especially around lunar sunrise and sunset, when the sun’s light ...

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