Messier 40 is a double star, which is unusual for Messier's catalog, most other objects being either galaxies, nebulae, or star clusters. Most probably, it is an optical double star, i.e. a chance alignment of two independent stars at different distances. The two components are of visual magnitudes 9.0 and 9.3, and their separation on the sky is about 54 seconds of arc, having grown apart by several seconds over the years since Messier added them to his catalog. The brighter of the two stars, which is estimated to have about the same mass as our sun, seems to be considerably more luminous than Sol and the fainter of the two, which may be just a bit more massive, is apparently much less luminous and is likely much closer to us. The actual distances of the pair are quite uncertain and have been estimated to be anywhere from 300 to 2,000 light years from Earth. The double lies about 170 minutes from Megrez, the star in the Big Dipper that joins the handle to the bucket. It is also only about 16 minutes NE of the 5.7-mag star 70 UMa. which is a bit off the upper right corner of this image.

Image taken January 24, 2012, with the C-14 operating at F:7 Exposure was 75 seconds on the ST-8