Messier Objects

From South Dublin Astronomical Society

The Messier Objects are a collection of Deep Sky objects first catalogued by Charles Messier. While searching for comets, Charles came across several diffuse objects with his little telescope. The first of these was in Taurus. When he realised this was not a comet due to it remaining in the same location night after night, Charles started what has now become known to us all as the Messier Catalogue. The purpose of this catalogue was not to identify interesting objects in the night sky, but rather to tabulate the objects which Messier saw which could be confused as a comet.

The Messier objects are not arranged in any kind of order. Messier simply noted them down as he found them. For example, you may be looking at M44, the Beehive cluster in Cancer, then you move on to the nearest object, M67, which is also in Cancer. The list contains almost the full range of deep-sky object types, as well as a few mistakes. The only type of deep-sky object not represented on Messier’s list are Dark Nebulae. The list has 40 galaxies, 28 globular clusters, 25 open clusters, 6 open clusters with a surrounding nebula, 4 planetary nebulae, 2 bright nebulae, 1 supernova remnant and 4 mistakes. These mistakes are also interesting; M24 is a bright patch in the Summer Milky Way. M40 is a double star with no associated nebulosity. M73 is an asterism of four stars while M102 is a duplicate entry of M101. It could be argued that the Messier Catalogue contains the best examples of each type of deepsky object. M31, the Andromeda Galaxy, is potentially the best galaxy in the sky, while M13 is regarded by many observers, in the Northern Hemisphere anyway, as the best globular cluster. M45, the Pleiades, contends with M44, the Beehive cluster, for the title of best open cluster while M42, The Orion Nebula is often regarded as simply the best deep-sky object of all. One difficulty for Irish observers is the low declination of some of the Messier objects, particularly objects round the Sagittarius area. Keep in mind though that Messier observed all of these objects from Paris, so it might be an idea to pack your binoculars next time you head off on holidays.

In late March every Messier object is visible in the night-sky on the same night. Many amateur astronomers since the 1960s have taken part in what has been dubbed the Messier Marathon, a race to view all the objects on the list in one session.

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