Since the invention of the telescope 400 years ago, astronomers have rapidly discovered countless celestial objects. But how does one make sense of it all? Astronomer and former NASA Chief Historian Steven J. Dick brings order to this menagerie by defining 82 classes of astronomical objects, which he places in a beginner-friendly system known as "Astronomy's Three Kingdoms." Rather than concentrating on technicalities, this system focuses on the history of each object, the nature of its discovery, and our current knowledge about it. The ensuing book can therefore be read on at least two levels. On one level, it is an illustrated guide to various types of astronomical wonders. On another level, it is considerably more: the first comprehensive classification system to cover all celestial objects in a consistent manner. Accompanying each spread are spectacular historical and modern images. The result is a pedagogical tour-de-force, whereby readers can easily master astronomy's three realms of planets, stars, and galaxies.