Pluto’s demotion from “planet” status to “lame Kuiper Belt resident” ahem “dwarf planet”/”planetoid” continues to be the subject of deep nerd rage. Many of us who grew up with Pluto-as-planet feel that modern astronomers are messing with our childhood memories. Others just make shirts and move on.

Today I bring you C.G.P. Grey’s beautifully reasoned discussion of why Pluto is or isn’t a planet, what the Kuiper Belt is, the history of planets, and (most fundamentally) what the word “planet” has meant over the millennia.
via Mental Floss

Continue reading, and check out the video here