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The far side of the Moon is the side which always faces away from the Earth, due to tidal locking. Due to libration, about 18% of this far side can be seen at one point or another through telescopes.

Culturally, there are many stories, some very old, about the near side of the Moon and its features, including the rabbit and the man in the moon and mythological moon beings.

Considering that the far side of the moon was only properly observed in the 1960s, how long ago did a human culture start forming an idea of the far side of the moon as a place? Was it when the first observations suggested that planetary bodies and the Earth were round? Was it earlier than that?

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    $\begingroup$ Probably prehistoric. That the sun and moon are "ball shaped" is implicit in, for example Ancient Egyptian which is right at the start of history. There were surely prehistoric people who thought the same, which in turn implies a far side. But being prehistoric, there are no records $\endgroup$
    – James K
    Nov 22 at 17:20
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    $\begingroup$ related:- astronomy.stackexchange.com/questions/44361/… $\endgroup$
    – Connor Garcia
    Nov 22 at 17:50
  • $\begingroup$ Like @JamesK says, we can only be sure for as far back as there are records. The idea is at least as old as Shi Shen, a Chinese astronomer from the 4th century BCE: en.wikipedia.org/wiki/…. $\endgroup$
    – Connor Garcia
    Nov 22 at 18:00
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The great scientist Johannes Kepler wrote a very unusual work called Somnium ("The Dream"). It is sort of a cross between a science fiction story and a scientific description of the Moon.

Somnium began as a student dissertation in which Kepler defended the Copernican doctrine of the motion of the Earth, suggesting that an observer on the Moon would find the planet's movements as clearly visible as the Moon's activity is to the Earth's inhabitants. Nearly 20 years later, Kepler added the dream framework, and after another decade, he drafted a series of explanatory notes reflecting upon his turbulent career and the stages of his intellectual development. The book was edited by Ludwig Kepler and Jacob Bartsch, after Kepler's death in 1630.

https://en.wikipedia.org/wiki/Somnium_(novel)#Development

Somnium was first published in 1634. And no doubt it described how (though not why) the Moon was tidally locked to the Earth. In fact it gives different names to the two hemispheres of the Moon.

Levania is divided into two hemispheres called Privolva and Subvolva. The two hemispheres are divided by the divisor. Privolva never sees Earth (Volva), Subvolva sees Volva as their moon. Volva goes throughout the same phases as the actual Moon.

https://en.wikipedia.org/wiki/Somnium_(novel)#Plot_summary

So as early as 1634 readers interested in science could find a description of the near side of the Moon that always sees the Earth and the far side of the Moon that never sees the Earth.

And I expect that any previous scientists and philosophers who wrote about the moon would have noticed that the pattern of light and dark areas - or at least as much of it as was in sunlight at the moment - was always the same, and thus that the Moon always kept the same side facing the Earth. And that would prove that there was a side of the Moon that never faced the Earth.

So I expect that philosophers and scientists knew that there is a far side of the Moon which always faces away from Earth for thousands of years.

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    $\begingroup$ Fascinating, thank you for taking the time to describe what I suppose is an extremely early Western science fiction! $\endgroup$ Nov 24 at 9:42

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