Christopher Graney

Christopher Graney

Christopher Graney is an astronomer and historian of science with the Specola Vaticana (the Vatican’s astronomical observatory) in Rome and the Vatican Observatory Foundation in Tucson, Arizona (home of the Vatican Advanced Technology Telescope on Mt. Graham).

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LEFT: Bernard Vaillant, “Portrait of Christiaan Huygens,” 1686. RIGHT: Sizes of planets and sun, from the 1698 ‘Cosmotheoros’ of Christiaan Huygens.

The Earth Is a Planet; Not All Planets Are Earths

PART IV: In the 1800s, the idea of a Plurality of Worlds was challenged by the fact that, just as stars are not all other suns, planets are not all other earths — and that even on those planets that might be other earths, inhabitants might not naturally spring out of the ground.