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 & abbreviations encountered in amateur & professional astronomy, are explained clearly & 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 & moons of the solar system, many individual comets, stars & asteroids, observatories & spacecraft. There are 57 line diagrams & 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 & invaluable reference book.