That California resolution makes far more sense than the nonsense adopted by four percent of the IAU, most of whom are not planetary scientists. Their decision was immediately rejected by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA's New Horizons mission to Pluto.

The IAU definition makes no sense for two reasons. One, it states that dwarf planets are not planets at all. That is like saying a grizzly bear is not a bear. It is also inconsistent with the use of the term "dwarf" in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies.

Second, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto's orbit, according to the IAU definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another is simply unusable.

The controversy could easily be solved if the IAU amends its 2006 resolution to make dwarf planets a subcategory of the broader term "planet."

Tyson is wrong about Pluto. It is a planet because unlike most objects in the Kuiper Belt, it is large enough to have pulled itself into a round shape--a condition known as hydrostatic equilibrium. When this happens, objects become geologically differentiated, just like the larger planets and unlike shapeless, inert asteroids and KBOs. An object in hydrostatic equilibrium orbiting a star (and not a star itself) is a planet. If that means we have dozens of planets, then so be it. The universe was not designed for our convenience.