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Originally Posted by freeztar
I have a couple questions about the moon photo you posted:
1) Are the dark areas dark because they are depressions? Or something else?
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I hope Bill won't mind if I leap in with some quick replies.
Yes, and Yes. These are the lunar mare, Latin for sea. The medieval astronomers imagined the moon as similar to the Earth and so thought these flat, dark areas were seas. Wholly wrong of course, but it has bequeathed us such wonderful names as Mare Serenatis, the Sea of Serenity, or Oceanus Procellarum, Ocean of Storms. They are depressed areas.
They are also something else in that they were filled with flood basalts early in the moon's history. This has made their surfaces especially flat, except where disrupted by later impact by asteroid or meteor.
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2. What are the wispy white trails emanating from the bright white spot? Is that ejecta?
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Absolutely right. They are ejecta. As such their composition and texture is different from the lavas of the mare. This is why they are still distinctive where they cross these.
