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04/15/2021 – Ephemeris – The Moon tonight – libration

15 Apr 2021, 04:01 UTC
04/15/2021 – Ephemeris – The Moon tonight – libration
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This is Bob Moler with Ephemeris for Thursday, April 15th. Today the Sun will be up for 13 hours and 30 minutes, setting at 8:28, and it will rise tomorrow at 6:56. The Moon, 4 days past new, will set at 12:14 tomorrow morning.

The crescent Moon tonight is in the constellation of Taurus the bull. The bright star Aldebaran will be just to the left of the Moon. In binoculars the dark oval spot visible on the Moon is the Sea of Crises or Mare Crisium a small dark lava plain. The Moon’s rotation is quite uniform, however its orbit isn’t circular, so the Moon’s appearance seems to rock a bit back and forth over the month. It’s an effect called libration. And one way to track that is to note how close the Sea of Crises is to the edge of the Moon. A week from now that sea will appear its closest to the edge. Astronomers call the edge of the Moon the limb. The phase line between day and night on the Moon is called the terminator. Now as the Moon is waxing, it is the morning or sunrise terminator.

The astronomical event times given are ...

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