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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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.
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