In 1784, French astronomer Charles Messier compiled a list of non-stellar celestial objects. He had no understanding of what these items—now known to be galaxies, nebulae, and star clusters—actually were; he just wanted to further the search for comets by listing the indistinct objects that might be mistaken for them. Designations from his catalog are still used to refer to some nebulae and star clusters—for instance, M1 is the Crab Nebula and M45 is the Pleiades. What is a “Messier Marathon”? Discuss