Tycho Crater

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• 17 of 1968
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The Moon soars high overhead tonight, taking aim at the Pleiades star cluster. Binoculars will help you see the little dipper-shaped cluster through the lunar glare. And as long as you have the binoculars out, take a look at the Moon, too. In particular, look in the southern hemisphere, along the dividing line between night and day, for the crater Tycho. It's visible to the unaided eye, too, but binoculars provide a better view.

Tycho is one of the youngest of the Moon's large craters. It's about 50 miles across and three miles deep, with a sharp mountain peak rising from its floor.

Tycho probably formed when a mountain-sized boulder slammed into the lunar surface. The impact blasted out thousands of cubic miles of material. Much of it formed long streamers that are visible as bright "rays" around the crater. The longest rays stretch a fifth of the way around the Moon.

The rays helped scientists determine when Tycho was formed.

One of the rays stretches to a mountain range about 1300 miles away. The crew of Apollo 17 landed in those mountains, and found that something had triggered a massive landslide there -- probably the impact of material blasted out of Tycho. From samples returned by the astronauts, scientists determined that the event happened 108 million years ago -- meaning that's probably when Tycho was formed.

The asteroid that created Tycho might have had a deadly sibling, and we'll talk about that tomorrow.

Script by Damond Benningfield, Copyright 2007

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