In case anyone wants to pursue the research, the 1945 #ArthurKoestler book is The Yogi And The Commissar, and Koestler makes a one-word malapropism in an astronomical metaphor describing how little Western Europe and North America hear about the U.S.S.R.'s East.
This is then carried into the title of Helena Sikorska's 1947 book about Poland and the Soviet Union, T.S. Eliot explaining the connection in xyr introduction to that book. And contemporary articles that then mention the book include Eliot's quote of Koestler.
Undoubtedly, the error was helped to spread by the advent of the Space Race.
This is the earliest that I've found of 'dark side' mis-used for the far side rather than for the night-time side (as found consistently in many examples before then, including the 1771 Britannica's entry for Astronomy). So Koestler seems to be the origin, in print at any rate.
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@Photo55You should read some #ArthurCClarke. Xe correctly used 'far side' for the far side, of Luna and other moons, most notably in the famous 1968 essay Explorations In Tomorrow talking about, amongst other things, the idea of putting an observatory on the lunar far side. We British actually do know our #astronomy.
This other-sense-of-dark argument is a post-hoc bad justification for a purely 20th century malapropism that appears to have its origin in a 1945 book by Arthur Koestler.
Prior to that in the 19th century, the 'dark side' is consistently the night-time half, because, of course, people can look at the phases of the moon and see that the dark bit is sometimes the bit that's near to us. Thomas Dick was a Presbyterian minister and science popularizer, and xe was clear about this:
> When the earth is at D, and the moon is at the position marked 3, the dark side of the moon is turned toward the earth, and she is consequently invisible.
