Are they still teaching kids the nine planets?
I’ll fill in the actual situation with Pluto, then let you know what I do in my class. Pluto is now a “dwarf planet” after the August 24, 2006 reclassification by the IAU. There are now only 8 official “planets” in our solar system. A “planet” is a celestial object that: 1) Is in orbit around the Sun. 2) Has enough mass so that its self-gravity overcomes rigid body forces and it assumes hydrostatic equilibrium (this means that it is close to a sphere in shape). 3) Has cleared the neighbourhood of its orbit of planetesimals. A “dwarf planet” is a celestial object that: 1) Is in orbit around the Sun. 2) Has enough mass so that its self-gravity overcomes rigid body forces and it assumes hydrostatic equilibrium (this means that it is close to a sphere in shape). 3) Has NOT cleared the neighbourhood around its orbit. 4) Is not a satellite of another body. The basic difference is in number 3. The IAU recognizes three dwarf planets (last time I checked): Ceres, Pluto, and Eris. They believe t
