Charles Messier’s list of Things That Are Not Comets turned out to be his lasting fame in astronomy. It contains many of the most spectacular objects in the night sky. Unfortunately, M40 is not one of them. It’s unclear why Messier even put it on his list. It’s a double star. It isn’t a nebula, galaxy or star cluster which can look like faint, fuzzy blobs and look similar to a comet. Messier 40 is the double star just above center in the frame. It’s decidedly not fuzzy, doesn’t masquerade as a comet and generally leaves everyone scratching as to how it ended up on the list.

Astronomy magazine reports that an object was reported in this area by Johannes Hevelius and that Messier couldn’t find it so he added this double star. This was the wrong action. He should have said, “I can’t find the thing you said where you said it was” and not recorded anything. Instead, he picked his best guess as to what he was supposed to find and added that.

So….we have a double star on the Messier list. It’s not even a binary star system but an optical double. The stars are not gravitationally bound but Messier had no way of knowing that.

Knowing that this was not going to be an interesting subject, I only did a very short integration, just 18m 40s. However, it turns out there are a number of small, faint galaxies in the background that can be found with a little effort. That was an unexpected bonus though not surprising once I thought about it.

You can find the technical details on astrobin.