Messier object

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During the second half of the 1700's, a French astronomer named Charles Messier was engaged in the hunt for comets as this was how one gained fame as an astronomer at the time. From all accounts Messier was quite successful at comet hunting, discovering no less than 13 comets [1]. Despite this, Messier is more famous in our time for a list of objects he created to help him in his comet hunting.

History of Messier's List

During his hunt for comets, Messier would often come across fuzzy objects that in his telescopes looked like comets, but weren't. In order to not to accidentally report one of these objects as a comet, Messier compiled a list of these nebulae and star clusters. It is for this list, published in it's final form in 1781 as the Catalogue des Nebuleuses et des Amas d'Etoiles (Catalogue of Nebulae and Star Clusters)[2]. The originally published list contained 103 objects. Messier used his own observations as well as those from other astronomers to make the list.

The astute reader will note that there are 110 objects on modern Messier lists. The final seven objects were added later by others, based on Messier's notes and letters after the publishing of the Catalogue des Nebuleuses et des Amas d'Etoiles. M110 was added in 1966 when it was discovered that Messier had discovered this object in 1773[3].

Modern Usage

Messier simply numbered the objects in his list in the general order in which he became aware of them. Thus the numbers are scattered about the sky without any real order. To distinguish the Messier number from other numbered astronomical objects, the letter "M" is usually placed in front of the object's number. So the 45th object on Messier's list would be shown as M45.

Because of the technology of the day, Messier's equipment was the equiavalent of about a modern 4" refracting telescope[4]. This puts virtually all the objects on the list within the reach of modest amateur telescopes and hence Messier's list is quite popular with amateur astronomers. Magnitudes of Messier's list range from the brightest, M45 at 1.5 to M76 and M97 at 12.0.


  1. l'Observatoire de Paris, Charles Messier, (Accessed 15 June 2009)
  2. Messier, C. 1781, Connoissance des Temps, p 227-267, available at: (original) or (English Translation)
  3. SEDS Messier Database, Messier 110, (accessed 15 June 2009)
  4. l'Observatoire de Paris, Messier's telescopes, (accessd 15 June 2009)
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