A Dictionary of Astronomy

A Dictionary of Astronomy

A Dictionary of Astronomy

A Dictionary of Astronomy


Astronomy is expanding almost as rapidly as the universe itself, and the proliferating scientific jargon can sometimes baffle even the most dedicated amateur. Now, in some 4,000 concise, up-to-date entries, this dictionary cuts a clear path through the maze of complex technical language, offering full, clear definitions drawn from all aspects of astronomy. Compiled by Ian Ridpath, a fellow of the Royal Astronomical Society, and an expert team of contributors, A Dictionary of Astronomy contains the most recent entries from astrophysics and cosmology to galaxies and time. Here are succinct definitions for the Big Bang theory, comets, eclipses, Magellanic Clouds, Mars, quasar, relativity, and variable stars. Entries on telescopes and other measuring devices, observatories, space missions, and recently named Solar System objects show how astronomers have explored the universe. The Dictionary also provides biographical entries on eminent astronomers from Copernicus to Edwin Hubble. From black hole to white dwarf, and from spiral galaxies to solar waves, A Dictionary of Astronomy opens a window on the universe for amateur astronomers everywhere.


Nearly 4000 entries in this Dictionary of Astronomy cover all aspects of the subject, from the smallest and nearest objects in the Solar System to the largest and most remote structures in the Universe. The terms and names it defines range from those in common use by amateur astronomers to those familiar only to professionals. Certain entries -- notably those dealing with the main objects in the Solar System, and the principal entries for stars and galaxies -- provide coverage in greater depth. Relevant concepts from physics are also defined.

Entries are ordered alphabetically on a letter-by-letter basis up to the first comma. This principle gives, for example, the sequence of headwords diverging lens, D layer, D lines, dMe star, Dobsonian telescope; but Hubble, Edwin Powell, Hubble classification, Hubble constant. Headwords which include a number are ordered as though the numbers were written out in words. For example, 47 Tucanae will be found under F, and 61 Cygni under S. The same principle applies to headwords in which a number follows a letter, such as H I region ('H one'), H II region ('H two'), and H O maser ('H two O'). SO galaxy is ordered as if spelt 'S nought', with apologies to American users who would look under 'S zero'. Similarly, headwords containing a Greek letter are ordered as if the letter is spelt out: for example, is treated as 'H alpha'.

Where several variants of a given term exist, our choice of headword for the main entry was strongly influenced by The Astronomy Thesaurus, compiled for the International Astronomical Union by Robyn and Robert Shobbrook. The present dictionary is the first to benefit from this valuable listing, which helps to standardize astronomical terminology.

Variants of a term are included in the dictionary with a cross-reference directing the reader to the main entry. For example, a reader looking up either microwave background radiation or cosmic microwave background will be referred to the main headword, which is cosmic background radiation. Cross-references within an entry are indicated by prefixing the term with an asterisk, thus: *cosmic background radiation. Other cross-references are printed in small capitals, for example 'see BIG BANG'.

Different senses of the same headword are numbered 1, 2, . . . . Where necessary, these numbers are appended to cross-references, as in dispersion (1), for example.

Some terms do not have a full entry, but are defined in a different entry, in which they are printed in italic. For example, a reader looking . . .

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