 You may have noticed that many of the most photographed deep-sky objects have a popular name like Orion Nebula, but also a catalog name. And in the case of Orion Nebula, that would be M42. But what is this M in the M42? Well, the M actually stands for Messier, and Messier is the astronomer who came up with this catalog and published it. In this video, I'm going to explain who Messier was, what his catalog is all about, and why this Messier catalog is still so popular today hundreds of years later. Charles Messier was a French astronomer that lived in the 18th century in Paris, France, and he was obsessed with comets. So much so that I think it'd be perfectly fair to call him a comet hunter as his sort of occupation. He discovered 13 comets in his lifetime, but Charles Messier, he had a problem with his comet hunting. He would often find these nebulous faint fuzzy objects in the night sky and think, mm-hmm, that might be a comet, only to observe it for a little while and realize, well, it's not moving relative to the other stars. So it must be some fixed object out there in space. At the time, astronomy was visual only. It was before cameras, and the telescopes weren't nearly as good as they are today. So there was no concept yet of other galaxies. What we now know are galaxies were all lumped in then with nebulae, so it was the great nebulae in Andromeda. So to get back to the story, Messier had an idea, which is record a list of the positions of all of these things that were definitely not comets because they were fixed in the sky. At first, this was probably just for his own benefit, so he could quickly rule them out when searching for comets, but at some point he started publishing his lists in the French scientific journals. And this was how Messier's catalogue became one of the first published catalogs of what we now call Deep Sky Objects. And partly because it was one of the first, it has had an enduring legacy, even when later there were, you know, efforts to make much more extensive catalogs of non-stellar objects, like the new general catalogue, NGC. Even after that, the Messier catalogue was still a go-to for the objects that are included in it. And let's talk a bit now about what is included. First off, Messier only observed from Paris, France. So these are all objects you can see from the Northern Hemisphere, and some of them only from the Northern Hemisphere. There are only 110 objects included. So for a point of comparison, the NGC catalogue has over 7000. But the great thing for us amateurs is all 110 objects in the Messier catalogue were observed with a 100 millimeter refractor from a rooftop in downtown Paris. And this means that they're all reasonably bright objects. And because there are only 110 of them, they make a really cool challenge. For instance, my friends, Galactic Hunter, published a fun Messier catalogue workbook so you can check them off when you observe them or photograph them. Many people also try to complete a Messier marathon, where in the spring you can actually try observing or photographing all 110 Messier objects in one night, something I'd really like to try someday. Other than the compactness of the list of just 110 objects, I think another reason the Messier catalogue still remains so popular is that many of the brightest showpiece objects in the Northern sky are included in the Messier catalogue for astrophotographers. To name a few, the Lagoon Nebula M8, Hercules Cluster M13, the Trifid Nebula M20, the Dumbbell Nebula M27, the Andromeda Galaxy M31, the Triangulum Galaxy M33, the Orion Nebula M42, the Whirlpool Galaxy M51, the Ring Nebula M57, Boads and Cigar Galaxies M81 and M82, and the Pinwheel Galaxy M101. And all those ones I just listed would be a great starting list for the beginner astrophotographer to take on. Then that's not to say that all the really photographic objects are included in Messier's catalogue. For instance, many of the large dim emission nebulae that are very colorful that I like so much were invisible to Messier, but can be picked up a lot easier with a long exposure on a camera. Well, as always, I could probably say more, but this is five minutes Friday, so we're going to end it here. Next week, I'll be talking about ways to measure and compare sky quality, including some methods like light pollution maps, the Bortle scale and sky quality meters. Until next time, this has been Nico Carver from NebulaFotos.com. Clear skies.