This is a detailed treatment of the scientific work done in the fields of cosmology and "exobiology" (i.e. extraterrestrial life). It is written for the layman, with paragraphs written in a smaller font that hammer out the technical details.
Sagan annotates the original Russian work of Shklovskii. Sagan's annotations help clarify some of Shklovskii's work by inserting examples and 'fer-instance's, offering opposing arguments, and telling charming tales in his incomparable way.
The book has three sections. The first deals with Cosmology, which is the study of the structure and composition of the universe. The second section deals with the origins of life, how it happened on Earth, and how life might form in extraterrestrial environments, such as on other planets. The third section details the search for extraterrestrial life.
The book will give a sense of awe for the reader who may not know, for example, that there are former stars in our galaxy which are as massive as our Sun, are the size of our Earth, and that spin 300 times a second! (These are the pulsars). The book also succeeds in giving the reader a sense of enormity both in the size and the age of the universe.
There are sections in the book that you will want to ignore because they are severely outdated. For example, there are several chapters dealing with the quest for life on other planets in our solar system, such as Mars. All of the Mars pictures in the book are of fuzzy images from ground-based observatories. This book was written before Voyager, Viking, and the Hubble Space Telescope. So when Sagan asks "Are there canals on Mars?" or "Are the moons of Mars artificial satelites?", you can just skip it (there aren't and they aren't).
On the other hand there is much relevent information that deal with radio contact among galactic civilizations (if there are such civilations). Here you can see the seeds of some of Sagan's later work in "The Cosmic Connection", "Cosmos", "Contact", and well others.
