What is a Messier Object?


By Dave Furry

While searching the sky for their quarry, comet hunters are essentially looking for “fuzzy patches of light” and are often frustrated if they see several objects that fall into that category but turn out not to be comets at all. This type of frustration prompted Charles Messier, a French astronomer in eighteenth-century France and avid comet hunter, to begin assembling a catalog of “fuzzy patches” in 1758 “so that astronomers would not confuse these nebulae with comets just beginning to shine.” Today we know this list as the Messier Catalog, which consists of 110 deep-sky objects that are worthwhile and relatively easy for amateur astronomers to observe. These “nuisance objects” (as Messier called them) make a great beginning project for amateurs who are just getting into observations of deep-sky objects.

Messier’s list was officially published in 1774 with 45 deep-sky objects, and in 1780 Messier supplemented his list with 23 more objects. By 1781 there were 35 additional objects posted (24 from a colleague) for a total of 103 objects. Finally, seven more objects were added in the 1920s based on notes from Messier and his colleague.

There were some cases of mistaken identity, however, and it is generally accepted that not all 110 objects are bona fide. These “mistakes” are:

  • M24 – Actually a bright area of the Milky Way in Sagittarius
  • M40 – A wide double star in Ursa Major
  • M73 – A small asterism (collection of stars) in Aquarius
  • M102 (NGC 5866)- mistakenly taken as M101

Over the course of time astronomers have given names to some Messier objects often based on common items they resemble:

M1       Crab Nebula (Taurus)

M44* Beehive Cluster (Cancer)

M8      Lagoon Nebula (Sagittarius)

M45** Pleiades (Taurus)

M11     Wild Duck Cluster (Scutum)

M51     Whirlpool Galaxy (Ursa Major)

M13     Great Hercules Cluster (Hercules)

M57     Ring Nebula (Lyra)

M17*** Omega Nebula (Sagittarius)

M64     Black-Eye Galaxy (Coma Berenices)

M20     Triffid Nebula (Sagittarius)

M76     Little Dumbbell Nebula (Perseus)

M27     Dumbbell Nebula (Vulpecula)

M97     Owl Nebula (Ursa Major)

M31     Andromeda Galaxy (Andromeda)

M104   Sombrero Galaxy (Virgo)

M42     Orion Nebula (Orion)

* Also known as ‘Praesepe’

** Also known as ‘The Seven Sisters’ or ‘Subaru’

*** Also known as the ‘Horseshoe’ or ‘Swan’ Nebula

An interesting fact is that all of the Messier objects may be observed during a single night! This is known as a “Messier Marathon” and may occur during a window lasting a few weeks between mid-March and early April. Here in Southern Colorado we are fairly well situated for such an event, as a latitude of around 25 degrees north (Pueblo is about 38 degrees north) is considered to be the best location to successfully complete a Messier marathon. Have fun!

Charles Messier’s 1807 sketch of the Andr9omeda Galaxy (M31):