If I look into the sky and I see two yellow dots it’s all stars for me. Then I hear one of them is mars and I’m like „ok, still looks the same“. How did the people hundred of years ago discover what’s a close planet and what’s a far away star?
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Yeah but we don’t really look at the stars nowadays. Before light pollution, reading, TV, radio, etc. Humans had stars at night. Not only did they stare at them long enough to recognize that some were different, planets, but they also knew what certain stars meant, for them. When one constellation was in one spot of the sky there was water at this site. When a constellation was in a different spot buffalo could be found at another site
Because planets have “retrograde” motion. Stars consistently move from east to west in the sky (keeping track of them over multiple days). Planets also generally move from east to west, but will have periods of time that they instead appear to move from west to east.
Eventually we figured out that it’s because the sun is the center of the solar system, and when a planet appears to be moving in “retrograde”, that is really when Earth, in its orbit, is moving past that other planet, in its orbit.
Well, it was hundreds of years ago and there was little to do. It was dark since light pollution was hundreds of years away. Copernicus and Kepler tracked movements and noticed that some of the ”stars” had unusual movements.
planet means “wanderer”
stars essentially have fixed positions in the sky, but planets move. when you see Venus (the morning star or evening star) you’ll note it’s position changes throughout the year because it’s moving.
stars, OTOH are so far away they are essentially stationary.
The night sky was very dark, except for the stars and planets, so on clear nights they’d spend a lot of time looking at the patters of stars in the sky.
They played connect-the-dots to find shapes that they could easily recognize: constellations. That made it easy to follow where the stars were in the sky and even give names to some of them.
They noticed that constellations moved up and down in the sky with the seasons, but the positions of the stars in a constellation, and constellations relative to one another, stayed the same. Except…
There were a small number of bright stars in the sky whose positions moved about — in one constellation one day, then moving to another in a few days or weeks. They weren’t part of constellations, but “wanderers” (or in Greek, “planētēs”). They didn’t know what stars or planets were other than lights in the heavens, but “planets” were wandering lights in the heavens.
As you get older you notice long term patterns, you can see the moon moving, notice stations, etc. I’m sure with nothing else to do you would get use to the sky and notice one of the “stars” moves around over time.
Stars more or less move all at once. Someone looking at the sky over time could notice some stars seemingly moving in separate directions to the rest of stars that also happened to appear brighter. Eventually they realized these things were separate bodies orbiting the sun.
This Wikipedia page is pretty cool, as it not only goes over the history of when they were discovered, but even mentions what the astronomers saw that tipped them off in the first place: [https://en.wikipedia.org/wiki/Timeline_of_discovery_of_Solar_System_planets_and_their_moons](https://en.wikipedia.org/wiki/Timeline_of_discovery_of_Solar_System_planets_and_their_moons)
Observing celestial phenomena was vitally important for early cultures. It wasn’t just a hobby, it helped them to keep track of the passage of time and therefore how to plan for the future. There’s a reason why so many ancient religious ceremonies are timed for certain celestial phenomena; that was the basis of their calendar.
So, of course, any culture that uses the stars as a way to plan their lives will get to learn familiar constellations and categorize the brightest stars. And that’s what the planets originally were to them: stars. Specifically, stars that wandered. They didn’t stay in their constellations, they moved around the sky. Thus, the Greeks called them planets, which came from the same root as their word for ‘wanderer’.
They didn’t know they were closer. What they did notice is that almost all the dots in the sky stayed in the same positions relative to each other and the sun. Almost all.
A select few dots changed positions relative to everything else from day to day. Those moving dots are the planets (the word “planet” has it’s origins in a Greek word for “drifting”).
Go outside tonight. Find the 3 brightest stars. Mentally note roughly where they are at that time of night. Repeat once a week. You will discover some planets.
Mercury is tough to spot unless you live on the ocean, because it’s only visible close to the horizon. Jupiter, Mars, and Venus are *bright*. You will find them. Once you’ve found those, Saturn is pretty easy too. They all travel in the same arc across the sky.
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