Planets technically means "wandering stars", right? It makes sense that understanding earth to actually be an object the same as they are would be near the end of developing astronomy initially.
Just means "wanderer," yeah, because the planets are, from a classical astronomer's perspective, the only objects in the sky that move relative to the sky itself. Stars move over the course of the night (as the Earth rotates around its axis), and stars move over the course of a year (as the Earth revolves around the sun), but they don't move
relative to one another in a way perceptible with the naked eye.
(This is one of the major arguments for geocentrism: if the Sun is the center and everything revolved around it, then observations of stars six months apart should show them moving relative to one another. We don't see this, therefore the Earth must be stationary. This is a totally sound argument: the issue is that the stars are
so far away that you can't perceive their parallax movement unaided. The ancients weren't stupid or conceited when they said the Earth was the center of the universe, geocentrism was legitimately the best explanation of the data they had available to them without telescopes.)
Planets are the only regularly-appearing object in the night sky that don't do this, and so ancient astronomers always cared about them a lot, because they were obviously special. This is why the Sun and the Moon make the list of classical planets: while not fitting the modern astronomical definition of planets, they are definitely celestial objects that move relative to the sky. And the fact that there are seven such planets that you can see with the naked eye (The Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn) may explain why seven is such a common magical number to find across cultures across the world.
(You can also understand a bit better why people freaked out about comets: it was a thing in the night sky that moved, like a planet, but it
wasn't a normal planet, it appeared without warning and disappeared the same way. As any person who uses a complicated system knows, when something that normally doesn't change suddenly starts exhibiting weird behavior, you
worry. The skies are so unchanging and predictable in their courses that they were used for telling time and navigation in an era without mechanical clocks, and deviations from that are legitimately scary!)
