There have been only a handful of famous deep sky "catalogs," including Charles Messier's, which was the first and remains the most famous. Messier was a comet hunter, and in the late 1700s he published a list of 109 objects in the sky that were not comets.

"The Messier's catalog of 109 'non-stellar' objects is still used by amateur astronomers as a guide to interesting objects to view and image. In 1995 the notable English astronomer and broadcaster Sir Patrick Moore published his own catalog of a further 109 objects, to complement the Messier catalog and provide an extended list of fascinating targets for amateur astronomers. He called it the Caldwell Catalog (Sir Patrick's full name is Patrick Alfred Caldwell-Moore), the 'M' designation having already been used by Messier. Some of the objects included are Caldwell 11 (The Bubble Nebula), spiral galaxy Calwell 30, and Caldwell 49 and 50 (The Rosette Nebulae).Along with Messier's list and Herschel's list of mostly faint 'non-stellar' objects, the Caldwell objects are now programmed into many automated telescope controllers. This allows all of these objects to be located easily even by newcomer astronomers. The Caldwell objects are just as spectacular as the 'M' objects, especially when using the large telescopes and the sensitive CCD cameras readily available today.The Caldwell Objects and How to Observe Them comprehensively describes all of the 109 Caldwell objects, with specific advice on how to find them (if necessary with a 'Go-To' telescope), how to visually observe or image them, and how to image-process the results. There is information about the optimum astronomical equipment to use for each object and, for those who prefer to make sketches, there is advice on drawing these extended objects at the eyepiece."

Sir Patrick Moore, Observer Extraordinaire.- The Caldwell Objects.- How to Visually Observe the Caldwell Objects.- How to Observe the Caldwell Objects Digitally.