The term 'cosmology' derives from Greek, essentially meaning the rational or scientific understanding of the cosmos, a word which to the ancient Greeks carried connotations such as 'order', 'regular behaviour' and 'beauty' (it is no accident that the words 'cosmology' and 'cosmetology', or 'cosmos' and 'cosmetics', are so similar). The wildly ambitious claim that the universe can be described rationally—that it is a cosmos, not a chaos—had its origin in ancient Greek natural philosophy, which consequently must occupy a central place in any comprehensive history of cosmology. Although in Chapter 1 I refer briefly to the cosmological views of non-Western cultures, the present book is concerned with the development of the scientific understanding of the universe, which effectively means that it is a contribution to the history of science in the European cultural tradition. Incidentally, although attempts to understand the universe in scientific terms go back to the very birth of science, until the twentieth century the word 'cosmology' was rarely used in a scientific context. The first books that carried the word in their titles date from the 1730s. As will become clear, cosmology did not have a professional identity until after the Second World War. Strictly speaking, there were no 'cosmologists' before that time, only scientists who ocassionally dealt with questions of a cosmological nature. Although it is a bit anachronistic to refer to these scientists as 'cosmologists', it is a convenient label and I have made no particular effort to avoid it.
The domain of cosmology is a frightening concept, the universe or the cosmos in the sense of everything that has (or has had, or will have) a physical existence, whether matter, energy, space, or time. I use the two words 'cosmos' and 'universe' synonymously, and also do not distinguish them from the word world. In German and the Scandinavian languages this all-encompassing concept is sometimes known as 'all'; compare the German Weltall. Cosmology in the traditional sense refers principally to the study of the structure of the universe, what in the seventeenth century was often known as cosmography, a term which stresses the mapping of the universe and which could also refer to what we would consider as geography today. Indeed, when Ptolemy's famous geographical work (Geographia) was first translated into Latin in 1406, it carried the title Cosmographia. Whereas cosmology and cosmography were sciences dealing with a static world, cosmogony means literally the study of how the universe came to be what it is and so includes a temporal dimension. However, the term is not widely used any longer, and today the evolutionary aspects of the universe, including its so-called creation, are included under the label 'cosmology'.
Confusingly, cosmogony and cosmography often referred to the planetary system (its formation and description, respectively) rather than the universe as a whole, as may be exemplified by Petrus Apianus' Cosmographia of 1524 and Henri Poincaré's Hypothèses cosmogoniques of 1913. Neither of these works was about cosmology, in the present meaning of the term. Cosmophysics may come closer, but this was originally a name employed for a mixture of astrophysics, meteorology, and geophysics, with little concern for the universe at large. The term may first have been used by the German Johannes . . .