My book attempts to describe the present position of Cosmogony and of various closely associated problems of Astronomy, as, for instance, the physical state of astronomical matter, the structure of the stars, the origin of their radiation, their ages and the course of their evolution.

In a subject which is developing so rapidly, few problems can be discussed with any approach to finality, but this did not seem to be a reason against writing the book. Many years have elapsed since the last book on general Cosmogony appeared, and the interval has seen the whole subject transformed by new knowledge imported from observational astronomy and atomic physics. It has also witnessed the growth of an interest in the results of Cosmogony, which now extends far beyond the ranks of professional astronomers, and indeed beyond scientific circles altogether.

With this in my mind, I have tried to depict the present situation in the simplest language consistent with scientific accuracy, avoiding technicalities where possible, and otherwise explaining them. As the book is intended to be, first and foremost, a rigorously argued scientific treatise, the inclusion of a substantial amount of mathematical analysis was inevitable, but every effort has been made to render the results intelligible to readers with no mathematical knowledge, of whom I hope the book may have many.