Recommended podcast: Radioab -- when the moon was close and the days were short (14 minutes)

The title of this podcast, "The Times they are a Changin," does not refer to the Bob Dylan song, but to the fact that, on a cosmic scale, we can't take anything for granted.

The Radiolab hosts weave commentary with clips from experts to explain that, about 4.5 billion years ago, when the moon was created, it was about ten times closer to the Earth than it is today and days were around six hours long.

(The podcast has a second part -- a six minute long conversation with Neil deGrasse Tyson).