In the current news about Pluto’s demotion, I read a passing reference that when Ceres, Vesta, Pallas and Hygiea were first discovered they were classified as planets for several decades before being reclassified as asteroids. First I heard of this. Is it true that if you had asked somebody back around 1825 how many planets there were, he’d have told you twelve?
In 1825 it would have been 11, and they would not have included Neptune (which was discovered in 1846). Four asteroids were discovered in 1800 to 1807, then Astraea in 1845 (making 12 planets), then Neptune would have been the 13th planet.
But then in the next decade (1847-1856) another 36 asteroids were discovered, and in 1857-1866 a further 49 (making 91 up to the end of 1866). Some time during these discoveries astronomers would have decided that they couldn’t all be planets, and demoted the lot of them to take it back to 8.