Pluto in size of Charon and Pluto has prompted some astronomers to call it a double dwarf planet. The system is also unusual among planetary systems in that each is tidally locked to the other, which means that Pluto and Charon always have the same hemisphere facing each other. From any position on either body, the other is always at the same position in the sky, or always obscured. This also means that the rotation period of each is equal to the time it takes the entire system to rotate around its barycenter. In 2007, observations by the Gemini Observatory of
Definition of planet in astronomy, there are dwarf stars, which are stars, and dwarf galaxies, which are galaxies, so it's a term no one can love, dwarf planet." Mike Brown noted in an interview with the Smithsonian that, "Most of the people in the dynamical camp really did not want the word "dwarf planet," but that was forced through by the pro-Pluto camp. So you're left with this ridiculous baggage of dwarf planets not being planets." Conversely, astronomer Robert Cumming of the Stockholm Observatory notes that, "The name 'minor planet' [has] been more or less synonymous with 'asteroid' for a very long time.