M109: The identity of M109

Henk Bril has recently found possible evidence that Pierre Méchain, when discovering this “nebula near Gamma UMa,” may have actually observed NGC 3953, not NGC 3992 which is usually identified with M109. He found this when investigating Fortin’s revision of Flamsteed’s Atlas Celeste of 1795, as revised by French astronomers Lalande and Méchain.

See Henk’s story at


Henk’s notion can be augmented by the manuscript note of Charles Messier on this object, apparently a semi-literal write-down of Méchain’s discovery note to him:

“Nebula near Gamma UMa, same right ascension a bit near this star and 1 deg .. more south. Discovered by M. Méchain on March 12, 1781.”




More on M109 (NGC 3992):

More on NGC 3953:


As of this time, we are certainly aware that several scenarios are possible: Méchain may have discovered NGC 3953 on March 12, 1781, and on March 24, 1781, Messier saw either this one also, or – in that case discover – NGC 3992. Messier’s mentioning of this object within the published description of M97 indicates that at least he had really seen some object here.


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