This revised edition contains 4,000 up-to-date entries written by an expert team of contributors, under the editorship of Ian Ridpath, renowned author and broadcaster. Covering the most recent space exploration missions and latest technological development, this authoritative dictionary covers everything from astrophysics to galaxies and time. World-wide coverage of observatories and telescopes, and major entries on supernova, Big Bang theory, and stellar evolution, make this an invaluable reference source for students, professionals, and the amateur astronomers.