Sadly, I cannot embed this video (hey BBC, it's the 21st century! Hello? Hello? Free publicity here! Sigh.), but it's worth clicking to see this clip of the brilliant comic (and even better skeptic) Stephen Fry hosting the game-like show "Quite Interesting" -- a program where he quizzes comedians over various topics, though it's really just an excuse to make lots of pretty funny jokes. In this particular clip, he asks the celebrity contestants how many moons the Earth has, and the answer is... well, surprising. Let me know when you're done watching, OK? I'll wait. Great, finished? Good. Stephen was talking about the asteroid Cruithne (pronounced GORR-bleccchhh), which orbits the Sun on a path very similar to the Earth's, but slightly more elliptical. Back when the object was first determined to have this odd orbit, I wrote about it on the BA News page. It wasn't named Cruithne yet, so you won't see the name there, but the basic idea is how this object is not really a moon of Earth, but not totally independent of us either.
In fact -- and I hate to say this, as I follow Stephen on Twitter (heck, everyone does), I like him very much, and I'm fond of his personal assistant, too -- but his information on the show was wrong! There are at least four other objects like this, but in fact none of them is really a moon of the Earth (see item 7 on that list). They aren't bound to the Earth gravitationally, so they aren't moons. We don't really have a name for this type of object, as far as I know -- a fact I find interesting, as in general classes of asteroids with similar orbits are typically named after the first one of their kind discovered. Maybe nobody can pronounce Cruithne (it's actually pronounced GLAVIN-heyhey) so they didn't want a class named after it. I'll note, to be fair, that at least one of these objects was discovered after that episode of QI aired, but some were known beforehand. Still and all, the point is that these objects are definitely not moons of the Earth.
"We have late-breaking news...it's evidently pronounced Ecky-ecky-ecky-ecky p'kang! Zroop-boing! mrowvm..."
Also, I can't leave without pointing out the background image they use in that clip; I recognized it immediately. It's a Hubble picture, one I'm intimately familiar with (check the Biographies link for that image). I wrote the supplemental essay for that picture, too. It's nice to see it unexpectedly like that. I worked so hard on that data I got sick of it -- my task was to count the stars in it and get their positions and brightnesses at various wavelengths, and I spent a long time writing buggy code that never quite did the trick -- but now I can appreciate the picture for how pretty it is. In fact, I think the image probably did better as just a pretty picture than any impact it had scientifically. Certainly it was seen by more people as a backdrop for QI than read about it in the astronomy journals! And that's something that is, really, Quite Interesting. And hey! Pssst. Stephen! If you read this, tweet a link to it and I'll release you from your coffee-making duties. Ask your PA for details.Tip o' the dew shield to Kyle VanderBeek.