The Messier Catalog - Where To Point Your Telescope
- Brandon Holloman
- 6 days ago
- 4 min read
Have you ever wondered where to point your telescope? If you’ve ever looked into a listing of astronomical objects, you’ve likely noticed that many of the galaxies, nebulae, and more are labeled with an M followed by a number. That means the object in question is part of the Messier Catalog, a listing of 110 astronomical objects used worldwide that features some of the best targets for any telescope.
The Comet Blacklist
The Messier Catalog is the creation of Charles Messier (pronounced meh-see-AY), a French comet hunter born in 1730. Messier was inspired to become a comet hunter when he witnessed the Great Comet of 1744. When close to Earth and the Sun, comets can be plainly visible and obvious to the naked eye, even more so with a telescope. But smaller and more distant comets were hard to discern. Messier would spend his nights scanning the skies with his 4-inch refracting telescope in search of undiscovered comets.
But Messier faced a problem. He would often come across objects that weren’t comets. Whenever he found such an object, he had to take the effort to confirm that it wasn’t a comet. In order to save time, Messier created a list of every object he confirmed wasn’t a comet. That way he, as well as other comet hunters, wouldn’t need to waste time every time they accidentally came across the already confirmed not-comet object.
In the end, the final version of the catalog published by Messier listed 103 different objects, but after Messier’s death, careful review of his notes revealed 7 additional objects discovered by him and his assistant after the final version of the catalog was published, bringing the total up to 110.
From Avoid These to Look at These
The intention of Messier in compiling the list was to create a catalog of objects for comet hunters to avoid. However, the Messier Catalog took on a life of its own and became the exact opposite: an essential guide. At the time of its creation, the Messier Catalog was the most complete listing of astronomical objects that had existed. And even in modern times, where we have more complete catalogs, the Messier Catalog is important to amateur astronomers, as it is a list of objects discovered with what is considered a modest telescope by today's standards, making them all relatively easy to spot with a modern scope. Some objects, such as M3, don’t even have a proper name, and are instead typically referred to by their Messier Catalog designation.
Types of Messier Objects
The Messier Catalog contains some of the most prominent examples of all five primary types of deep-sky objects—including diffuse nebulae, planetary nebulae, open clusters, globular clusters, and galaxies. They are all among the largest, brightest, and/or closest to Earth of their kind, which is what makes them valuable to study, even for professional astronomers.
Of the types of objects found in the catalog, diffuse nebulae and planetary nebulae are two different types of clouds of gas found in space. A diffuse nebula is a cloud of gas that has all the ingredients for new stars to form, hence their nickname as stellar nurseries. Popular diffuse nebulae include M8: the Lagoon Nebula, M16: the Eagle Nebula, and M42: the Orion Nebula. Planetary nebulae are the opposite, and are actually the clouds left behind when a red giant star collapses into a white dwarf, leaving behind its outermost shell of material as the planetary nebula. The Dumbbell Nebula (M27) and the Ring Nebula (M57) are popular examples. Despite the name, these nebulae have nothing to do with planets. There’s also a single supernova remnant—a third type of nebula which is the remains of the explosion of a dying star—in the catalog with the Crab Nebula as M1.
Open clusters and globular clusters are two different types of tightly packed groupings of stars. Open clusters are composed of up to thousands of stars, and are what is left behind after the gas of a diffuse nebula has been dispersed, leaving only the newborn stars. Open star clusters are not permanent, and the stars will eventually drift apart. There are many open clusters in the Messier Catalog, but the most well-known is the Pleiades as M45. Conversely, globular clusters are closed, which means they are gravitationally bound and therefore relatively permanent. A globular cluster can contain hundreds of thousands of stars. Unlike open clusters, they are found outside of the disc of the Milky Way Galaxy, orbiting it like a satellite orbits the Earth. Many globular clusters don’t have proper names and instead go by their Messier designation, such as M2 or M3, but others, like the Hercules Globular Cluster, M13, do.
The final type of object found in the catalog are galaxies. They are the large groups of billions of stars which are completely separate and independent of our own Milky Way Galaxy. Galaxies can come in spiral, elliptical, or lenticular shapes. The most well-known and commonly viewed galaxy is M31, the Andromeda Galaxy, which is the nearest major galaxy to the Milky Way. Other galaxies in the Messier Catalog that are great to observe are M51, the Whirlpool Galaxy and M104, the Sombrero Galaxy.
If you’re interested in seeing some of the best your telescope has to offer, then the Messier Catalog is perhaps one of the best places you can go for suggestions. Anything on the list can be seen with relative ease, especially on a dark night away from light pollution. There are even those astronomers who love the Messier Catalog so much, they participate in Messier Marathons to spot as many Messier Objects in one night as possible.
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