PAUL
Welcome to Idaho Skies for January 25th, 26th, and 27th. We’re your hosts, Paul…
RACHEL
…and Rachel.
PAUL
The moon reaches the third quarter phase on the night of the 26th and morning of the 27th.
RACHEL
The third quarter moon will rise over Boise at 11:38 PM. That’s often too late for most people, but it is a weekend. If you aim your binoculars at the moon, you will notice a large round sea in the upper right of the moon. This is the Sea of Rains or Mare Imbrium. Along its lower right edge is the Apennine Mountains. You should also notice two large craters in this lunar sea.
PAUL
The large crater inside of the Sea of Rains is named Archimedes and the other one at the top is called Plato. Archimedes and Plato are very old craters that formed after a giant impact created the Sea of Rains. Astronomers know this because these craters have flat and dark interiors. In other words, they’re not bowl-shaped.
RACHEL
The decay of unstable elements led to the creation of magma, or liquid rock beneath the lunar surface. In time, the less dense magma oozed out of cracks or fissures in the Sea of Rains. That magma became sheets of lava that filled in the giant impact scar. It took many layers of lava to fill in the Sea of Rains. That’s why this lunar sea looks dark and is free of many large craters.
PAUL
Astronomers know that Archimedes and Plato formed after the impact that created the Sea of Rains and before lava filled in the impact site. If they had formed first, then the impact responsible for the Sea of Rains would have obliterated the craters. If they formed after the moon’s magma cooled, they would have never filled with lava. So when do astronomers think these craters were created? About 3.8 billion years ago.
RACHEL
That’s Idaho Skies for the 25th, 26th, and 27th of January.
PAUL
Be sure to follow us on Twitter @IdahoSkies for this week’s event reminders and sky maps.
For Idaho Skies this is Paul…
RACHEL
…and Rachel.
RACHEL
Dark skies and bright stars.
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