Thursday, November 27, 2008

The Far Side of the Moon

Photo of the moon. Dark Side of the Moon album cover.
Photo of the moon and Pink Floyd's Dark Side of the Moon album cover. 

I was reading an excerpt from Eudora Welty (1909-2001)’s One Writer’s Beginnings in Lapham’s Quarterly (see previous post) and I started thinking about the moon. In the excerpt Welty talks about her misunderstanding about where the moon “rose” and in one story she wrote that the moon rose in the west. 

After reading that I realized that I wasn’t exactly sure I could speak to the mechanics of how the moon rotates around the earth. In particular, I thought the “dark side” of the moon was, well, always dark. You see? The arts can lead you astray because I always think of Pink Floyd’s Dark Side of the Moon and assumed that it is always dark. 

Well, after some schoolin' at Travelmarx headquarters I’m happy to report that the dark side of the moon is not truly always dark and is probably more aptly called the “far side of the moon”. The moon is tidally locked to the earth which means that the same face of the moon always faces the earth. 

And now the tricky part: “A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner.” Or, in other words, the moon takes 27.3 days to rotate once on its own axis as well as revolve around the earth. The sticking point for me was squaring the fact that the moon keeps the same face towards earth yet rotates around its axis. You can think of it this way: You are in the middle of a merry-go-round and a friend is facing you at the edge of the merry-go-round. After one complete revolution of the merry-go-round, your friend has made one revolution around you *as well as* one on his own axis. Think about it.


  1. it's not too hard...think of 2 marbles touching. one marble in the middle spins in place, the other rotates around the first marble while also spinning... am i off? probably... i did get an F in physics...

  2. my head gets tidally when i think about this.

  3. The moon doesn't appear to spin to us on earth. But you are on the right track. I got an A in physics but that just goes to show you that a good grade doesn't prove anything.


All comments go through a moderation process. Even though it may not look like the comment was accepted, it probably was. Check back in a day if you asked a question. Thanks!