# number of planets in the solar system # over history # # Year Number_of_planets 0 7 incl. Sun, Moon 1543 6 Copernicus adds E, subtracts S,M 1781 7 Uranus 1801 8 add Ceres 1802 9 add Vesta 1804 10 add Juno 1808 11 add Pallas 1845 12 add Astraea 1846 13 add Neptune 1847 16 add Hebe, Iris, Flora 1848 17 add Metis 1849 18 add Hygiea 1850 21 add Parthenope, Victoria, Egeria 1851 23 add Irene, Eunomia # the term "asteroids" is adopted for the minor planets # during the period 1851 - 1868 or so # one can't pick a hard date, so I'll pick 1852 # 1852 8 subtract the asteroids 1930 9 add Pluto 2006 8 subtract Pluto 2016 8 today