The age of merely looking at the heavens, of mapping and cataloguing the positions of the stars down to fainter and fainter limits, is past. Throughout that long period the pace of astronomical discovery was necessarily very slow and for centuries it remained virtually static. The invention of the telescope and then the spectroscope brought about an acceleration in the rate of progress which has continued unabated to the present day. Scarcely a year now passes without some spectacular advance being made, so that today, with the co-operation of modern techniques in physics, chemistry, rocket technology and biology, many of the older notions have been completely overthrown and new ideas set up in their place. And now the rapidly developing techniques of rocket research have made it possible to carry astronomical instruments beyond the atmosphere which confines our visual and photographic observations to an extremely narrow band of the electromagnetic spectrum. Now we are able to view the universe in ultra-violet and infra-red light, and by X-rays and radio emissions which are otherwise almost completely absorbed by the atmosphere.

Each problem that is solved, however, only serves to present us with a host of others in increasing complexity. The boundaries are being pushed back steadily, it is true, but the realm of the partially understood and the totally unknown is still as great as ever, and it is with this vast no-man's-land of astronomy that this book is concerned. It deals, amongst other subjects, with astronomical instruments and their application, recent discoveries in the solar system, stellar evolution, the exploding stars, the galaxies, quasars, pulsars, the possibilities of extraterrestial life, relativity, etc. With this book as a guide, the reader cannot fail to experience some of the tremendous fascination of present-day astronomy and its innumerable unsolved problems.