The revised second edition of this established dictionary contains over 4,300 up-to-date entries on all aspects of astronomy. Compiled with the help of thirty-four expert contributors under the editorship of renowned author Ian Ridpath, the book covers everything from space exploration and the equipment involved, to astrophysics, cosmology, and the concept of time--plus biographical entries on eminent astronomers and worldwide coverage of observatories and telescopes. The appendices include tables of Apollo lunar landing missions, the constellations, and a table of planetary data. The entries have been fully revised and updated and fifty new entries have been added. The content is enhanced by web links which are regularly updated on a companion website.