The Face of the Moon

Enlarged image

Plato at sunrise is reproduced here. Plato was one of many lunar features that was suspected of change in the nineteenth century, and the crater floor had been the subject of a special study by W.R. Birt several years earlier. The problem was that some of the craterlets periodically vanished and reappeared, and the floor itself appeared to get darker as noon approached, rather than lighter, suggesting that some kind of vapors or vegetation gradually covered the crater as the lunar day advanced. The variability of Plato was still being advanced by many lunar observers right up until the 1960's. The observed change, however, is entirely illusory.

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