13. Where can Mare Orientale (the Eastern Sea) be found? [Trick question alert!]

Answer:

(B) On the western limb of the Moon. The reason is that the reflecting telescopes most often used by astronomers show the Moon upside down, so that objects in the west (such as Mare Orientale) appeared to be in the east. The confusion in terminology didn't matter very much until NASA started seriously planning to send astronauts to the Moon in the 1960s, and the astronomers were persuaded to switch their definition of east and west to agree with everyone else's. According to Don Wilhelms, old-time lunar scientists still have trouble remembering what is supposed to be east and what is supposed to be west.

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