On October 7th 1959, the soviet Luna 3 probe took the first picture of the far side of the moon.
It has been known since ancient times that the moon was a sphere. It would have doubtless been observed that the moon always seemed to present the same face to earth. The back face would have been a complete mystery, and I imagine suspect to much speculation.
The moon's libration allows attentive astronomers to see up to 57% of the lunar surface. Nevertheless, the thought of the unknown on the moon's far side must have been very tantalising to many astronomers, in the same way the appearance of Ceres and Pluto was to us prior to 2015, if not more strongly so.
Are there any interesting or notable historical theories on what the far side of the moon looked like or contained?