ABSTRACT
At the beginning of his Epitome astronomiae Copernicanae, Kepler lists the following components of astronomy, all of which he considers necessary to the science of celestial phenomena (Kepler 1953: 23). The astronomer's task, he says, consists of five main parts: historical, to do with the recording and classification of observations; optical, to do with the shaping of the hypotheses; physical, dealing with the causes underlying hypotheses; arithmetical, concerned with tables and computation; and mechanical, relating to instruments. The first three areas, adds Kepler, involve mainly theory; the last two are more concerned with practical aspects.
