Today in History: August 24
The International Astronomical Union published an article, “Definition of a Planet in the Solar System: Resolutions 5 and 6,” ten years ago today. (The link is to a PDF file.)
In popular culture, what the IAU did ten years ago today was demote Pluto (seen above) from one of the classic nine planets of the solar system, the nine whose names we all grew up memorizing and reciting, to one of several or many or thousands of “dwarf planets,” leaving us with eight planets. Schoolchildren everywhere possibly find it odd that this elicited as much controversy as it did.
The article employed in an official way a term that had been around since the early 1990s: dwarf planet. A dwarf planet is an object that is massive enough to be a ball (in scientific terms, it is a spheroid that is in hydrostatic equilibrium) and orbits the Sun, but it is not massive enough to have cleared its lane through space.
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