Astronomy, being the oldest of the exact sciences, has a very long historical tradition going back many thousands of years. For the greater part of this time, the study of the skies has been inseparable from astrological and religious traditions. Indeed, in the past, astronomy was more intricately woven into the fabric of civilization than is the case today. Not until the time of Galileo and Newton do we find the scientific aspects of astronomy to be distinguishable from its mystical overtones. To review the long evolution from the many primitive views of the cosmos to our own complex picture would be a vast task, and one which would be out of place in an encyclopaedia of modern astronomy. Our purpose, therefore, is to take four of the significant themes and show how these were slowly developed by individual scientists to give us our present understanding.
The selection of topics for a limited discussion must be somewhat arbitrary. We have chosen to describe the following major trends:
The development of theories of the planetary system, with particular
reference to the impact of these theories on man’s understanding of
the Universe and to the thrust given to the branch of mathematics
known as celestial mechanics.
Methods by which cosmic distances are evaluated and their relationship to
the model of the Universe adopted in working out the distances.
The rise of astrophysics as a separate discipline, and the attempts of
physicists to deduce the nature of stars and the Sun through analyses
of the known laws of physics.
The discovery of the vast Universe beyond our Galaxy and the calibration
of the extragalactic distance scale.
The adoption of this scheme brings out more clearly the main steps involved in the calibration of the distance scale for example at the expense of a strictly chronological story. Since our aim is to show how parts of astronomy developed in practice, rather than to give a detailed account of every small advance and major setback, we feel justified in abandoning the traditional order of presentation.
Our story does not begin in deepest prehistory. We could have started with a survey of primitive astronomy and protoastronomy throughout the world, drawing in the contributions of Babylonia, Central America and neolithic Europe, together with description of alleged observatories such as those at Stonehenge and Carnac. Although this is in itself a fascinating tale, it cannot be linked in an unbroken chain to the present day. Hence we shall begin in the classical world of the Mediterranean, where the earliest planetary models that we can still describe with certainty were invented.