Held up by the heliopause? Floored by the flatness problem? Intimidated by MACHOs? With this dictionary there is no need to be defeated by such astronomical jargon. These terms, along with almost 3,200 more words, names and abbreviations encountered in amateur and professional astronomy, are explained clearly and concisely in a style that is authoritative but accessible. In addition to a comprehensive selection of specialist terms, entries include all the constellations, all the planets and moons of the solar system, many individual comets, stars and asteroids, observatories and spacecraft. There are 57 line diagrams and 7 tables of additional information at the back. Anyone involved with astronomy, either professionally or as a leisure interest, will find this dictionary a handy and invaluable reference book.