M40

Winnecke-4

Typ:	Star System
Constellation:	Ursa Major
Size:	0.8'
Distance:	0.51 kLj
Brightness:	9.7 mag
Position:	RA:12h 22m 12.5s DEC:+58° 4′ 59″
Max. height:	81.91°, Mar. (midnight at +50°N)
	Show in Stellarium
Discovered:	Charles Messier, 1764
Details:	Read more on Wikipedia

Charles Messier got a hint from a colleague to check for some nebulosity in a particular spot. The only thing he could find at the specified position was this pair of stars, which he then catalogued as M40.

Nowadays we know, that this is not even a double star system. While seemingly neighbours from our perspective they are in fact not related. So M40 is effectively an error within the Messier Catalogue.