You are here

Moon and Companions

March 28, 2013

Although the Moon looks quite bright in our night sky, its surface is actually one of the darkest of any major body in the solar system. On average, it reflects only about a tenth of the sunlight that strikes it back into space, making the Moon as dark as charcoal.

There is one prominent bright spot on the Moon, though - a crater named Aristarchus. Although it’s tiny as seen from Earth, it’s such a contrast to the surrounding landscape that it’s visible to the unaided eye. It’s near the lower left edge of the Moon as the Moon rises this evening, flanked by the star Spica and the planet Saturn.

Aristarchus is about 25 miles across, and a couple of miles deep. A mountain peak rises about a thousand feet from its floor. It’s surrounded by bright “rays” of debris that were blasted out by the impact that created it.

Observations by Hubble Space Telescope and spacecraft in lunar orbit show that the crater floor contains a lot of minerals that are rich in titanium. They probably came from far below the surface, and were brought to the surface by the impact.

There’s some evidence that the area around Aristarchus is volcanically active. Observers on the ground have reported seeing flashes of light or odd glows in the area, including in the crater itself. And instruments have revealed traces of a radioactive gas. That could mean that gas sometimes erupts from below the surface - briefly adding to the luster of this bright crater.


Script by Damond Benningfield, Copyright 2013

Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.