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A Cepheid in the Spiral Nebula M31



The photographic plate of Messier 31 on which Hubble discovered the first Cepheid variable star in a spiral nebula. The objects marked "N" are novae. At first Hubble marked the object in the upper right corner as a nova, but he soon realized it was a variable and marked it "VAR!"

Image courtesy of the Hale Observatory
Brought to you by the
Center for History of Physics, a Division of the
American Institute of Physics  

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