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Why do some impact craters have rays?

7 Jan 2019, 14:00 UTC
Why do some impact craters have rays? NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

When you look at the full Moon through binoculars or a small telescope, one of the most prominent features on the surface is the crater Tycho. It's an impact feature about 86 kilometers wide, situated near the southern edge of the Moon's near side. It's relatively young — maybe 100 million years old — and fresh craters tend to be brighter, making it easy to spot.

But that's not why it's so prominent: It's the rays, the collection of long, bright features pointing radially away from the crater. Tycho sports rays hundreds of kilometers long, some over a thousand.

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