Discovered by Charles Messier 1764.

This faint double star was found by Charles Messier when he was searching for a nebula which was - erroneously - reported by the 17th-century observer Johann Hevelius in this vicinity. According to his catalog description, Messier did not see any nebulosity associated with them. As Messier had measured the position of these stars, he gave them a number in his catalog.

This fact gives some suggestion on how this catalog was compiled: Messier collected positions while he was cataloging the star clusters and nebula which could be taken for comets. M40 was apparently the last one he recorded when he was busy in checking the reports available to him in 1764, of previously recorded "nebulae."

The double lies 16' NE of the 5.7-mag star 70 UMa. It forms a rectangular triangle with the faint barred spiral (type SBb), NGC 4290 (12.5 mag, 2.5x1.9 arc minutes angular diameter, receding at 2885 km/s which corresponds to about 125 million light years distance).