Pluto gets the short bus.

This post is about 3-4 days too late, but in case you didn't hear, Pluto is now no longer considered a planet according the International Astronomers Union.

Its a bit sad, especially for those who grew up with Nine Planets. But in truth it is probably for the best. The IAU had worked with two definitions of a planet. The first and most generous was that anything with enough mass to overcome other shaping factors and was not a satellite of another planet would be considered a planet. This had the advantage of allowing Pluto to be a planet, but had the disadvantage of letting all the new discoveries in the Kuiper belt (including the one unofficially nicknamed 'Xena') as well as a couple of members of the Asteroid belt. The second definition, which the Astronomers agreed upon says that not only must it have the other qualifications, but also must have cleared its immediate area of other satellites. Meaning that Pluto has too much traffic in its space lane.

Radical changes like this are nothing new. In the 19th century, children were taught that the Asteroid belt denizen Ceres was an actually planet. That was changed after a period of discussion.

It may seem petty, but this debate has actually caused much distraction in the astronomical community. The Bad Astronomer perhaps put it best when he said that now that this is all over we can get around to studying these things, rather than endlessly debating what the heck they are. Yes, that was the level of distraction in some quarters.

As I mentioned to someone else: Pluto isn't gone, its just not allowed to play with the big boys anymore. It may also be required to wear a helmet.