`Cosmogony' now refers to the origin of the universe or, most of the time, to the origin of planetary systems. The latter meaning came about because until relatively recent times it was believed that the cosmos is not much larger than the solar system. Thus, the original meaning of `study of the origin of the universe' also automatically meant `study of the origin of the solar system'. The latter meaning was expanded to include the study of the origin of other planetary systems when it was realized that these exists, while the original, basic meaning regarding the origin of the universe is now usually considered to be part of cosmology.