My Very Eager Mother Just Served Us Nine --Just Nine, Make that Eight

Human beings have known about planets since shortly after they could stop running away from predators long enough to watch the night sky and realize that some of the specks of light moved with respect to the other specks of light. A few dozen millennia later, Copernicus theorized that the planets, including Earth, revolved around the sun. So, in the grand scope of history, taking another 463 years to decide exactly what a planet is doesn't seem like too long.

Yes, only five millennia after the Sumerians noticed Mercury, astronomers have agreed on what exactly makes a planet. As of today, a planet is something that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

For those of you paying close attention, item C eliminates Pluto, which is in an orbit teeming with Kuiper Belt Objects. Pluto, Charon, Xena, and the other round orbiting chunks in the Kuiper Belt will be officially classified as Dwarf Planets. Now, schoolchildren will have only eight planets to memorize--seven if, like my elementary school, their schools leave out Uranus until middle school to avoid the juvenile jokes about rectums.