1697: planets (S.S.4) Aug 7, 2019

Pluto was demoted from being a planet in 2006, but this was not the first time something like that's happened. The word 'planet' was not terribly meaningful throughout much of history. Classically, both the Sun and the Moon were considered planets, part of the "seven classical planets". The word 'planet' comes from two Greek words, πλάνης (planēs) and πλανήτης (planētēs). The former meant 'planet' like we'd think now but also 'star', and they both meant 'wanderer', describing anything moving in the cosmos.

See more from the Solar System Series here.