The Complete CD Guide to the Universe

Around 10,750 of the objects are double or multiple stars; the remaining 3000 or so represent the other classes of deep-sky objects. Double stars dominate this work for two reasons. First, for telescopes of modest aperture they are by far the most numerous type of object and second, double stars are usually bright enough to be easily observed from urban sites. The other deep-sky objects include many galaxies (1573 of them), and although dark-sky sites are of course best, many of these can be seen in skies that most amateurs would write off as hopeless for the task. There are 580 open clusters, 109 globular clusters, 148 planetary nebulae, plus a few others.