I couldn't find references as to who first noticed (wrote down) that the moon was tidally locked to the Earth. This, to me, doesn't seem obvious from first glance, and looks like something only found with cautious observations.

More specifically, I'd want to know when this first realized, from this question I gather that even acknowledging the moon as a moon took a long time, but the observation (or explanation of it) that it is tidally locked is missing from that.

Would be surprised if Aristarchus of Samos already noticed this!

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    $\begingroup$ Ptolemy had a hard time believing that the Earth rotated, which Aristarchus' model implied, so it might also be relevant to ask, who first suggested bodies in space rotated. The geocentric point of view changes things a lot and it defies all kinds of laws of physics, which, they didn't have before Newton, so, it's better if we don't judge. I think Galileo may have been the first to suggest the sun rotated, based on his study of sunspots and Isaac Newton was, I think, the first to set up a formula for conservation of angular momentum. Too many "I thinks" to try to answer though. $\endgroup$
    – userLTK
    Feb 11 '20 at 2:57
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    $\begingroup$ I think once you establish (believe) that Earth and the Moon and Sun are basically spheres (or close to it), you immediately require that some of them move regardless of which you believe is central or motionless (or any other system). At that point you're going to work out from tivial observation that the Moon always looks the same and shows only one face. So assuming tidal locking is almost trivial and could be done relatively early. Modelling this requires at least Newtonian gravity and I would not be surprised to discover Lagrange explained that, as he did so many things in Astronomy. $\endgroup$
    – StephenG
    Feb 11 '20 at 4:13
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    $\begingroup$ There's always History of Science and Math SE $\endgroup$
    – uhoh
    Feb 11 '20 at 11:36
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    $\begingroup$ @uhoh Should I flag asking for it to be transferred, or is that not a thing anymore? $\endgroup$ Feb 11 '20 at 20:16
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    $\begingroup$ @Yuri-M-Dias there are two ways I know of; 1) copy/paste to new site then delete here, 2) vote to close as off-topic yourself, and leave a comment encouraging others to do the same, and after it's closed then flag and suggest "migration" to HSM. Moderators generally refrain from actions like this unless first signaled by community voting. #2 is the most "standard" way. $\endgroup$
    – uhoh
    Feb 11 '20 at 21:21

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