What are Messier objects?

The complete list of 110 Messier objects is called the Messier Catalog. And they are classified in three broad categories, as either nebulae, star clusters or galaxies.

What are Messier objects?

The Messier list starts with 103 deep-sky objects by the 18th century French astronomer Charles Messier. Eventually, seven more additions in the 20th century, bring the list up to 110 objects. Specifically, these deep-sky objects refer to astronomical bodies other than stars or planets. The Messier objects all appear as fuzzy, nebulous patches in the sky.

The names of Messier objects come from their number in the original catalog by Charles Messier. For example, the Pleiades star cluster is number 45, Messier 45 or simply M45. In addition to their numbers, many Messier objects have common names, such as the Pleiades, aka the 7 Sisters.

Messier objects are easily observed with a small telescope. And a few are visible using only binoculars or even just the eye alone.

Since all the Messier objects are fairly bright, finding Messier objects is an ideal project for the beginning stargazer.

A Messier marathon: See all Messier objects

In addition, every year in March, all 110 Messier objects are visible during the course of a single night. Stargazers around the world take advantage of this coincidence and plan a so-called Messier marathon. Basically, participants use telescopes or binoculars and attempt to see as many Messier objects as possible throughout 12 continuous hours of darkness. In order to see them all, observations must start at sunset and end at sunrise the following morning. Anyone observing 100 or more objects is pretty happy with their results.

However, remember a few Messier objects are hard to catch because they are only visible very close to the horizon. For best results, use a Messier marathon search sequence list and hunt down the objects in order. First, right after sunset, find the galaxies M77 and M74. Last, just before dawn, catch the globular clusters M72 and M30 plus the asterism M73. The date for a Messier marathon is always on the new moon nearest the spring equinox. You can relax off and on during the night while waiting for the next batch of Messier objects to rise. Or enjoy other wonderful deep-sky objects keeping you busy all night.

A bit of history

Ironically, Charles Messier never intended to compile a list of deep-sky objects. Because Messier was a comet hunter, he began cataloging nebulous objects that are often mistaken for comets. In short, those nebulous objects also appear as visually diffuse bodies, just like a comet. Comets were important in the 18th century because astronomers were tracking their orbits. That data successfully validated Newton’s theory of universal gravitation. Messier is credited with discovering 13 comets. But ironically, Messier is remembered more for his Messier catalog than for his comet discoveries.

Out of the 110 Messier objects, 41 are Messier’s observations. The first edition of the catalog came out in 1774, containing only 45 objects. Successive editions expanded the list, with another edition appearing in 1781 bringing the total to 103 objects. Astronomy writer Camille Flammarion – also a Frenchman – added object number 104 from Messier’s notes. Finally, some astronomers published a revised version in 1967, bringing the total up to 110 Messier objects.

Messier lived and worked in Paris, France, at a latitude of 49 degrees north. Hence, he only could observe the entire northern celestial hemisphere, and about half of the southern sky. Consequently, this explains why some notable southern objects, like the globular cluster Omega Centauri, are not on the list. Plus, the bright Eta Carinae Nebula is not a Messier object. Also, the very obvious Perseus Double Cluster in the northern celestial hemisphere is not included on the list.

Messier 45, the Pleiades

Messier 31, the Andromeda Galaxy

Messier 13, The great globular cluster in Hercules

Messier 42, the Orion Nebula

Useful references for Messier objects

A nice reference for stargazers with a telescope is a book titled Deep-Sky Companions: The Messier objects, now in its second edition. Written by the renowned amateur astronomer Stephen James O’Meara, this book includes over 100 drawings from pencil illustrating the true visual appearance of Messier objects, as viewed from Hawaii with a small refracting telescope.

A similar website available primarily in Spanish, with some English, is the Visual Messier Catalog by Puerto Rican amateur astronomer Juan Luis Martínez. Like O’Meara’s book, Martínez presents his own telescopic drawings instead of photographs.

The SEDS Messier Catalog is a wonderful website with images and lots of information.

Last but not least, NASA has a beautiful photographic gallery of some Messier objects from the Hubble Space Telescope.

Bottom line: Messier objects are a list of 110 star clusters, nebulae and galaxies.