The magnitude system works quite well for quantifying the brightness of stars. We know that a 6th magnitude star will be barely visible to the unaided eye from rural areas, yet easily seen in even the smallest of telescopes.
The magnitude system doesn’t work as well for deep-sky objects. Consider the spiral galaxy M33 in Triangulum. Listed as a 6th magnitude object, it’s notoriously difficult to view in telescopes. M33 is elusive because its light is spread over an area four times that of the full moon. Defocus a 6th magnitude star until it’s that large and you’ll get the idea.
Another reason why M33 is such a demanding target is its location in a star-poor region of the late autumn sky. I usually find it by training my telescope on an area roughly 4 ½ degrees west and slightly north of alpha (a) Trianguli. You can also trace an imaginary line from the Andromeda Galaxy (M31) to the star beta (b) Andromedae, then extend an equal distance beyond (refer to the accompanying finder chart). In either case, begin a low power sweep of the area until you encounter a large, faint glow.
The key to observing M33 is to use an eyepiece that affords a field of view of at least 1½ to 2 degrees. One of the best views I’ve had of M33 was with a 4-inch f/4 RFT (the Edmund Astroscan) and a magnifying power of 16X. I’ve spotted it with 7X50 binoculars, and some observers even report seeing it with the unaided eye. The key, of course, is to conduct a search for M33 from a dark-sky site on a clear, moonless evening.
Numerous sources credit the discovery of M33 to Messier himself (in 1764); however evidence exists that the true discoverer may have been the Italian astronomer Giovanni Battista Hodiema over a century earlier.
M33 is part of the Local Group of galaxies that includes our Milky Way and the Andromeda Galaxy. It’s approximately half the size of the Milky Way and lies about 2.9 million light-years away.