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Page from Hubble's Notebook

Page 156-157 from Edwin Hubble's observation notebook. It documents the discovery of the first Cepheid variable star in the spiral nebulae M31. Initially Hubble suspected that he had found a nova, a star that quickly flares up in brightness and then slowly declines. For photographic plate number 331, Hubble noted "Nova suspected." For plate 335, Hubble wrote "confirm nova suspected …" But Hubble soon realized that he had found not a nova but a Cepheid-type variable star.

Image courtesy Norriss S. Hetherington
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