Moon of the Day - Charon

Today's moon is Charon, the largest moon of the dwarf planet Pluto.

Charon is a little different from the other moons we've discussed so far, in that its classification is somewhat open to debate. That's because the center of mass, or barycenter, of Pluto and Charon actually lies in the space between the two bodies, which means that they essentially orbit each other (here's what an ordinary planet-moon system might look like -- the barycenter is inside the planet). So is it still a moon? Or a binary planet? Does it matter?

We'll get the first ever close-up images of the Plutonian system when the New Horizons spacecraft arrives in 2015. I can't wait.