An illustrated encyclopedia which includes some 140 extended essays on the solar system and deep-space astronomy, arranging them alphabetically from "Antimatter" and "Asteroids" through "White Dwarf Stars" and "X-Ray Astronomy." Entries cover not only the traditional subjects on which astronomers and physicists are more or less agreed but also the results of the latest research and discoveries: "Brown Dwarf Stars," "Extra-Solar Planets," and "Quantum Cosmology."

Essays are divided into various sections. Top matter lists the topic and its primary field(s) of study; an "overview" defines the topic and its importance; following this primary information is a section identifying "applications," "methods of study," or "knowledge gained." The final section, "context," places the topic in historical and scientific perspective.