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We knew the earth rotates, but the moon is tidally locked.

To tell that another planet is rotating, you have to be able to distinguish its surface (I guess?). Who first did this?

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    $\begingroup$ Good question!! $\endgroup$
    – uhoh
    Sep 11, 2017 at 16:31
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    $\begingroup$ Well, ... the moon is rotating, at one rotation per revolution. But that's a whole 'nother flame war. $\endgroup$ Sep 12, 2017 at 15:09
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    $\begingroup$ Hi Phillip. Your edit makes no sense. Also, it makes the accepted answer seem like it answers a different question (because it does!) I suggest you undo the changes and ask a new question if have one. $\endgroup$
    – JohnHoltz
    May 9 at 1:23
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    $\begingroup$ Ive undonne the changes. If you want ot ask a new question about moons, please ask a new question, rather than editing this one. $\endgroup$
    – James K
    May 9 at 3:40

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Mercury's surface was virtually unknown until Mariner 10 flew by and Venus is covered in clouds. Of the terrestrial planets, that leaves Mars.

It was likely Christiaan Huygens in November 1659 who first realised Mars was rotating when he tried to map it. His estimate of roughly 24 hours was fairly close.

I believe Galileo's earlier observations on Jupiter were with a telescope not powerful enough to resolve smaller 'surface' features (like the Great Red Spot), which may have either proven that Jupiter rotates, or at least that something on the surface is moving across it.

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    $\begingroup$ Nice answer! It might be better to link to both the Wikipedia article and the paper The Mapping of Mars separately, rather than linking to the footnote. (PDF also available). Wikipedia articles are constantly changing so a link to a footnote could disappear at any moment. $\endgroup$
    – uhoh
    Sep 11, 2017 at 23:45
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    $\begingroup$ Wikipedia supports your view on Galileo, suggesting that the first sighting was either by Hooke in 1664 or Cassini in 1665 - en.wikipedia.org/wiki/Great_Red_Spot . Galileo died in 1642. $\endgroup$
    – MartinV
    Sep 12, 2017 at 13:21
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    $\begingroup$ True, I imagine the Great Red Spot was identified before anything else of note (apart from the cloud bands), which was after Galileo's time. Interestingly, Galileo was among the first to infer that the Sun was rotating, by watching the movements of sunspots. $\endgroup$
    – user10106
    Sep 12, 2017 at 13:46
  • $\begingroup$ @user10106 The trouble is, we aren't sure. Cassini's observed feature may or may not have been the great red spot. We know it was there by the 1830s, but Cassini didn't note the red color (might be from telescope limitations, might be because he was seeing a different storm system), and nobody else reported a GRS-like feature for like 100 years. Then we started getting GRS reports and it has been continuously observed ever since. That suggests it may have formed in the early 1800s and was seen as soon as it was visible. $\endgroup$ May 9 at 16:04

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