Over 200 years ago, many of the celestial treasures on the following pages were cataloged by Charles Messier and William Hershel using telescopes primitive by today’s standards. These catalogs have formed the basis of most amateur astronomers’ targets for observing. The most famous is Messier’s Catalog of 109 objects. Despite their popularity with visual astronomers, Charles Messier’s choices were neither the brightest nor the most beautiful through the eyepiece. His list was compiled to define objects that might be confused with comets by other comet hunters – in other words, a list of potential mistakes. Entire regions of the sky, which fell outside of the area where comets might be found, were excluded from his list. This may explain how several bright deep sky objects such as the Double Cluster in Perseus were excluded.
In this century, the growth in quality and accessibility of amateur telescopes has driven an explosion of observing lists. The Herschel 400 list, compiled more than 30 years ago by the Ancient City Astronomy Club of Florida, includes objects selected from Herschel’s General Catalog that would “challenge” observers with telescopes 6 in. or larger. In 1995, Patrick Moore published the Caldwell list (his legal last name is Caldwell-Moore) of 109 objects, which includes both bright and dim objects excluded by Messier. His selection includes some small and challenging targets, not just the crowd pleasers. Most recently, in 2007, Stephen O’Meara published a list of 109 “hidden treasures” that seeks to fill in the gap left by the Messier and Caldwell lists. Like the Caldwell list, O’Meara’s list dips deep into the southern hemisphere.
These famous lists are excellent for visual astronomy but can be disappointing for the astrophotographer. For example, a sparse open star cluster sparkles at the eyepiece but can be uninspiring as an image. A small planetary nebula may be striking visually but may be too small to show interesting detail in a photograph. On the other hand, many nebulae that are faint to the eye can have striking texture and hue on long exposures. Spiral galaxies blossom into a rich diversity of shapes and colors.