Messier 102

Messier 102 (also known as M102) is a galaxy listed in the Messier Catalogue that has not been identified unambiguously. Its original discoverer Pierre Méchain later said that it was a duplicate observation of Messier 101, but more recent historical evidence favors that it is NGC 5866, although other galaxies have been suggested as possible identities.

Since the publication of the Messier Catalogue, a number of galaxies have been identified by different historians, professional astronomers, and amateur astronomers as corresponding to M102.

Messier 101 (also known as the Pinwheel Galaxy or NGC 5457) is a face-on spiral galaxy in the constellation Ursa Major. In a letter written in 1783 to J. Bernoulli, Pierre Méchain (who had shared information about his discoveries with Messier) claimed that M102 was actually an accidental duplication of M101 in the catalog. This letter was later published twice: First in original French in the Memoirs of the Berlin Academy for 1782, and second in German translation and somewhat rearranged by Johann Elert Bode in the Berliner Astronomisches Jahrbuch for 1786.

NGC 5866 (one of two galaxies commonly called the Spindle Galaxy) is a lenticular galaxy in the Draco constellation. This galaxy appears to closely match both the object description (by Pierre Méchain) in the printed version of the Messier Catalog of 1781, and the object position given by Charles Messier in hand-written notes on his personal list of the Messier Catalogue.

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