The true story of why Pluto isn’t a planet goes back further than you would think. It has a lot to do with our understanding of science at the time, and a lot more to do with surprising luck. I made this video a couple of days ago for the Khan Academy Talent Search. I hope you enjoy it. It will be interesting as we move into better telescope technologies that allow us to see further into the depths of the solar system and the universe. What strange mysteries will we find?