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Back Garden Astronomy - The Messier Catalog
Back Garden Astronomy - The Messier Catalog

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

How a Frenchman's 18th-century list of objects to avoid became the definitive catalog for amateur astronomers

Messier 13 by Laurie A.

Messier 13 by Laurie A.

For budding and seasoned stargazers in the northern hemisphere, the Messier Catalog is the most famous observing list of astronomical deep-sky objects. Within the 110-strong catalog are examples of every known deep-sky object — a good assortment of galaxies, open and globular star clusters, nebulae and one supernova remnant: the famous Crab Nebula in Taurus, which is also the first object in the catalog. It bears the designation Messier 1, commonly written as M1.

Messier's catalog has become so ingrained into astronomical lore that objects are commonly described by their Messier number. So 'M42' is often used in place of, or in addition to, the name of the object, in this case the Orion Nebula.

The irony of this useful catalog is that it was never intended to be a list of objects for observers to hunt down with their telescopes: rather, it was a list of objects to avoid. This is because Charles Messier, the French astronomer who created the catalog, was a comet hunter, and many comets appear as faint, fuzzy blobs in the sky — just as deep-sky objects do. So he assembled these deep-sky objects into a list of 'red herrings', in order to make sure they could be discounted during his cometary searches. He conducted these in his observatory, a wood and glass structure atop a tower in the medieval Hôtel de Cluny in Paris.

Growing Number
The Messier Catalog first arrived on the scene in 1771 as a list of 45 objects. Ten years later it had been expanded to 103, with some of the later observations being undertaken by Messier's assistant Pierre Méchain. The catalog stayed at this size for over 100 years. There were some interesting developments in the 20th century, as astronomers and historians made seven additions to the list. These were not just arbitrary objects, but ones that Messier and Méchain made observing notes about shortly after the final version of the catalog was published. It was only in 1967 when M110, a faint dwarf elliptical galaxy in the constellation of Andromeda, made its way into the catalog as the final officially recognised object.

There are several reasons why Charles Messier's 'list of objects to avoid when looking for comets' has become so readily accepted as targets to seek out with a telescope. One is that it isn't too long: 110 objects makes it a nice, manageable number. So manageable, in fact, that some amateurs like to undertake Messier marathons, where they endeavour to observe all 110 objects in one night.

Another reason is that Messier used a variety of different sized scopes in his comet searches, including a 3.5-inch refractor. The objects in his catalog don't need massively powerful instruments to be seen: they're within reach of small amateur telescopes.

Finally, it's a reasonably comprehensive list, encompassing almost all of the wondrous sights that novice stargazers would wish to see, many of them bright objects.

Of course, the Messier Catalog is not the only list — there are more than 110 objects out in space after all. The New General Catalog (NGC), for example, lists nearly 8,000 objects, followed by an extension known as the Index Catalog (IC) that adds more than 5,000 on top. You'll also find that many objects appear in multiple catalogs: M42, the Orion Nebula, is also designated as NGC 1976. However, the NGC and IC lists are little more than databases of deep-sky objects. They have less appeal for amateur astronomers because many of their entries are too faint to see without a professional telescope.

There is, however, one other list that's worth a mention: Patrick Moore's own compilation, the Caldwell Catalog. This is, in effect, an extension to the Messier Catalog. It includes many more bright, deep-sky objects that are perfect for you to train your telescope on from your back garden.

Top Naked-Eye Messier Objects

M42
RA 05h 35m 17s dec. -05° 23' 28"
The Orion Nebula is a vast cloud of dust and gas — what's known as an emission nebula, and is a star-forming region. It's easy to spot with just your eyes as a misty patch below the three belt stars in the constellation of Orion.

M45
RA 03h 45m 48s dec. +24° 22' 00"
The Pleiades, also known as the Seven Sisters, is an open star cluster in the constellation of Taurus. Depending on your eyesight and how dark the sky is at your location, you'll be able to see between six and 12 stars.

M13
RA 16h 41m 42s dec. +36° 28' 00"
The hundreds of thousands of stars that make up the Great Globular Cluster in Hercules are just visible to the eye from dark locations. It's one-third of the way south of a line between the stars Eta and Zeta Herculis.

M31
RA 00h 42m 42s dec. +41° 16' 00"
The Andromeda Galaxy is without doubt the most distant object visible to the naked eye, being about 2.8 million lightyears away. Find it in the constellation of Andromeda as a faint smudge in very dark, Moonless skies.

Top Small-Scope Messier Objects

M81
RA 09h 55m 33s dec. +69° 03' 55"
Looking at Bode's Galaxy in the constellation of Ursa Major with a 3- to 4-inch scope, you'll see it as the brighter of two fuzzy patches close to each other in the night sky. The second patch is another galaxy, the fainter M82.

M51
RA 13h 30m 00s dec. +47° 16' 00"
The Whirlpool Galaxy in the constellation of Canes Venatici is a face-on spiral galaxy. Small scopes reveal the basic shape and the smaller companion with which it is interacting. Larger instruments reveal more structure.

M3
RA 13h 42m 12s dec. +28° 23' 00"
This globular cluster, also in Canes Venatici, is an easy target for a small telescope - though it can be tricky to locate. It's one of the largest and brightest globulars in the sky; a small scope will reveal great detail and a compact core.

M57
RA 18h 53m 35sdec. +33° 01' 45"
The Ring Nebula in the constellation of Lyra is a shapely planetary nebula, and one of the easiest of its kind to observe. With a 3- to 4-inch scope it's easily seen as a misty but quite defined oval patch.

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Details
Date Taken: 02/06/2017
Author: BBC Sky at Night Magazine
Category: Astronomy

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