Messier was a professional astronomer, although he had never received any special training. Assistant of Delisle in one of the many private observatories that existed in Paris, he had an excellent sight and a talent for observation. He found no fewer than 20 comets, sometimes at the same time as his colleagues Pierre Méchain and Alexis Bouvard. These successes were such that he was given the nickname of “the ferret of comets.” Trying to find Halley’s Comet, he noted on September 12, 1758 an object that looked like a comet, but did not move and had a diffuse appearance; it was a nebula. In order not to confuse comets with these types of diffuse objects, he began a systematic search that led to the first extensive catalog of nebulae, containing 110 objects. It is this catalog, still in use as amateur astronomers can easily view the recorded nebulae, that made him famous.