The Caldwell Objects
For the newcomer to astronomy or deep sky observing, the different types of objects visible through a telescope may be rather confusing at first, so a brief explanation of how these objects fit into the great scheme of things may be useful. Stars are, rather obviously, the brightest objects in the night sky. Their nuclear reactions, created by fusion at their cores, illuminate the darkness. In every case, this fusion process is a controlled hydrogen bomb, with the control being provided by the immense gravity and the nuclear reactions arriving at an amicable agreement. The result of nuclear fusion illuminates the night sky. However, space is very, very big, and so even the stars only appear as pinpoints in the darkness. Essentially, stars are pretty much all we have to work with to provide any kind of visual illumination in the night sky. When we look at how many different categories of object are visible in the dark universe (and thus the Caldwell catalog), they all link back to stars in some way. Essentially this catalog, much like the Messier catalog, boils down to star clusters, galaxies, nebulae, and supernova remnants. All of these objects are made up of, or related to, stars in some way. Perhaps you may be able to point at dark nebulae, but we would argue here that a black cloud of dust is just an obstruction!