Wednesday, August 16, 2006

How many planets do we have?

In preparation for the possible IAU ruling on the definition of a planet, which might include all mostly spherical bodies orbiting the sun, I thought I should tell you a bit about the three "new" planets they're considering for promotion.


Ceres is the largest object in the asteroid field between Mars and Jupiter. It is named for the Roman goddess of grain, harvests, etc. Her Greek counterpart was Demeter. It was discovered quite a long time ago. Your best chance for seeing Ceres this year is right now. Ceres was in opposition on August 12. So get out your telescope and look to the skies!


Charon has been known as the largest moon of Pluto, but Charon is more than half the size of Pluto, so those IAU types are talking about declaring it and Pluto a "double-planet system." The two are locked in rotation so that they always show the same hemisphere to each other. Charon is named for the ferryman on the River Styx, which is why he's right beside Pluto.


Xena isn't really named Xena, but I don't like the provisional name of 2003 UB313. That's just hard to say (and type!). Hopefully at the IAU conference, they'll finally announce its name, too. 2003 UB313 is way out beyond Pluto, in the Kuiper Belt. Actually, Pluto's in the Kuiper Belt too. It's a big belt. Xena is named for the warrior princess who crossed swords with Hercules then starred in her own very popular television show. Like its namesake, the planet Xena (okay, the planet 2003 UB313) has a satellite named Gabrielle. No really. Sort of. Until they give it a real name.

No comments: