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The skygazer whose name is intertwined with deep-sky objects is Charles Messier who came to Paris as a young man in 1751. Messier quickly learned how to use the telescopes of his day and soon obtained the position of clerk at the Marine Observatory. Messier devoted his time to the most popular object for eighteenth-century skygazers: comets. As Messier scanned the skies over Paris, he discovered many annoying objects that appeared at first to be distant comets, but turned out to be merely uninteresting nuisances.
To help others doing similar work, Messier compiled and published a list of these objects. While Charles Messier's research on comets is now mostly forgotten, he won immortality with his list of nuisances, which turned out to contain some of the sky's most fascinating objects. Any object found on Messier's list is designated by the letter "M" in his honor, and a number indicating its place on the list. For instance, the Andromeda Galaxy is also known as M31.
Messier's original list contained only 45 objects. Subsequent additions by himself and others (the most recent in 1967) has lengthened the list to 110. Of course, other more complete catalogues of deep-sky objects have since been compiled. The New General Catalogue (NGC) from 1888 has over 13,000 objects and has since been expanded. Nevertheless, despite its limitations, we continue to use Messier's list. Its relatively small size turns out to be an advantage. With a minimum amount of equipment and a great deal of patience, one can see all the objects on Messier's list whose largest telescope was the equivalent of a modern 3 1/2-inch instrument.
When faced with the thousands of objects in the NGC the immediate reaction is to throw up one's hands and never look beyond the stars. Messier has reduced the multitude of deep-sky objects to something that we can feel a bit comfortable with. The list contains a variety of types of objects and for the most part, the most easily accessible of each.
Deep-sky observing is not for everyone. For one thing, without a telescope many objects are inaccessible. This does not mean that Messier objects can not be seen without optical aids, just that there is little point in doing so. Many of the these objects have an apparent magnitude hovering between five and six and are theoretically visible to the naked eye. According to the Norton's Star Atlas, M31 - the Andromeda Galaxy - has a magnitude of 4.8 and is "faintly visible with the naked eye". Perhaps -- but don't expect to be able to see it except on a night with an exceptionally clear sky.
And no matter how dark the sky, M31 is going to appear as a bit of whitish fuzziness -- hardly an impressive sight. This is true for all the bright Messier objects. Even with the aid of binoculars or a telescope, you will need the assistance of averted vision, dark adaptation and excellent sky conditions to see any details within a deep-sky object.
It is probably the very difficulty of observing deep-sky objects that makes them so attractive. They challenge a skygazer to operate at the very limit of his or her ability. The skills needed for observing deep-sky objects are the same ones utilized for closer objects. If the difficulties are on a higher level, so are the rewards.
Since most deep-sky objects can not be easily seen with the naked eye, you will have to "star hop" from a close-by star to bring them within the field of vision of your binoculars or telescope. Once the object is in focus, you may see wisps of green clouds or tremendous clusters of stars. Light has traveled for thousands or hundreds of thousands of years to be gathered onto your eye's pupil in order to convey an exotic sight from outside the Solar System.