M Numbers And The Messier Catalogue
by Kevin Brown : last updated: September 24, 2008Welcome back!
If you look at any astronomy books or star charts, you will quickly come across “M” numbers being used to identify objects in the sky.
For example, the Andromeda Galaxy (which is our nearest-neighbour, spiral galaxy and the furthest-away object you can see with the unaided eye) is referred to as M31.
The Messier Catalogue
M33 Triangulum Galaxy
These M numbers come from a catalogue of celestial objects that was created by the French astronomer Charles Messier, in the 1700’s and early 1800’s.
Messier was primarily a comet hunter. He was employed by the French authorities and given the task of finding Halley’s Comet, when it was expected to return to near the Earth in the late 1750’s.
Messier duly detected Halley’s comet as it returned. He also discovered about 20 other comets, during the course of his observing career.
While searching for comets, Messier kept a list of objects in the sky which might confuse a comet hunter. These were fuzzy objects that looked rather like comets, but which did not move across the sky in the way comets do.
Each of these comet-like objects was given a number, hence the Messier (or M) numbers.
Hence, the Messier Catalogue came into being and this is what Messier is remembered for today, not his comet hunting.
We know today that the Messier objects are a collection of star clusters, nebulae and galaxies.
You should be aware that there are other catalogues of similar objects.
Most of the Messier objects also have other classification numbers, from different catalogues. This can be confusing.
In addition to M numbers, there are also the commonly-used “NGC” numbers. These refer to the “New General Catalogue of Nebulae and Clusters of Stars”, which was drawn-up by the Danish astronomer Dreyer, in 1888.
So for example, the Andromeda Galaxy M31, is also classified as NGC 224.
Observing the Messier Objects
The Messier objects are some of the most interesting objects for amateur astronomers to search out and observe in the sky.
Messier’s catalogue contains 110 objects.
Some well-known examples are:-
M1, the Crab Nebula, in the constellation of Taurus
M42 and M43, which together make up the great nebula in the constellation of Orion
M51, the Whirlpool Galaxy, in the constellation of Canis Venatici
M57, the Ring Nebula, in the constellation of Lyra
The “Messier Marathon”
Nowadays, some observers attempt what is known as the “Messier Marathon”.
This challenge is to observe as many objects from the Messier catalogue as you can, in one night. The target of course, is all of them!
This is just about possible, although only at certain times of the year and from northerly latitudes.
As the Messier catalogue was compiled from the Northern Hemisphere, some of the objects are very difficult from the Southern hemisphere as they are very low in the sky.
