THE MOST EXPANSIVE DICTIONARY OF ITS KIND
`
`Oxford
`
`Astronomy
`9
`. 1!
`
`-
`
`
`
`UNIVERSITY OF TEXAS AT AU§TlN - GEN LIBS
`
`NIIIIH||l|\lilll\|\||HIM\||||Wl||||H\||$lilllWIHII|J|\|\liH|}||||HH||¢
`
`
`
`ASML
`1033
`3Ul565l.'1lH:.
`
`
`i
`
`o 5917 3015851946
`
`
`IAN RIDPATVI-I I_._....
`
`ASML 1232
`
`.‘
`~‘:£'__, "
`
`ASML 1232
`
`

`
`
`
`A Dictionary of
`
`Astronomy
`
`REVISED EDITION
`
`Edited by
`IAN RIDPATH
`
`OXFORD
`UNIVERSITY PRESS
`
`ii
`
`

`
`
`OXFORD
`UNIVERSITY PRESS
`Great Clarendon Street, Oxford OX2 6DP
`
`
`
`Oxford University Press is a department of the University of Oxford.
`It furthers the University's objective of excellence in research, scholarship,
`and education by publishing worldwide in
`Oxford New York
`
`Auckland Bangkok Buenos Aires Cape Town Chennai
`Dar es Salaam Delhi Hong Kong Istanbul Karachi Kolkata
`Kuala Lumpur Madrid Melbourne Mexico City Murnbai Nairobi
`Sao Paulo Shanghai Singapore Taipei Tokyo Toronto
`Oxford is a registered trade mark of Oxford University Press
`in the UK and in certain other countries
`Published in the United States by Oxford University Press Inc., New York
`
`© Oxford University Press ‘1997, 2003
`The moral rights of the author have been asserted
`Database right Oxford University Press (maker)
`First published 1997
`Revised Edition 2003
`
`All rights reserved. No part of this publication may be reproduced.
`stored in a retrieval system, or transmitted, in any form or by any means,
`without the prior permission in writing of Oxford University Press, .
`or as expressly permitted by law, or under terms agreed with the appropriate
`reprographics rights organization. Enquiries concerning reproduction
`outside the scope of the above should be sent to the Rights Department,
`Oxford University Press, at the address above
`You must not circulate this book in any other binding or cover
`and you must impose this same condition on any acquirer
`British Library Cataloguing in Publication Data
`Data available
`
`
`
`Library of Congress Cataloging in Publication Data
`Data available
`
`ISBN O19-860513-7
`1 3 5 7 9 10 8 6 4 2
`
`Typeset by Kolam Information Services Pvt. Ltd., Pondicherry, India
`Printed in Great Britain by Clays Ltd, St Ives plc
`
`iii
`
`

`
`59
`
`Bowen fluorescence
`
`components. The *Quadrantid meteor shower radiates every january from northern
`Bootes.
`
`boson A particle such as a *photon. a *meson, an atomic nucleus of even mass
`number (e.g. the commonest type of helium nucleus), or me hypothetical *graviton
`which has a zero or integer value of *spin. They do not obey the Pauli exclusion
`principle. Bosons are named after the Indian physicist Satyendra Nath Bose
`(1894-1974). See also FERMION.
`
`Boss General Catalogue (GC) Popular name for the five-volume General Catalogue
`of 33,342 Stars compiled in 1936-7 by the American astronomer Benjamin Boss
`(1880-1970). This catalogue contains positions and proper motions of all stars brighter
`than 7th magnitude over the whole sky. plus thousands of fainter stars for which
`accurate proper motions could be determined. It was a successor to the Preliminary
`General Catalogue of 6188 stars published in 1910 by his father, Lewis Boss (1846-1912),
`who also initiated the larger catalogue.
`
`boundary layer In a planetary atmosphere, the level of the atmosphere in direct
`Contact with the planet’s surface, In which friction between the surface and the air
`plays a significant role in determining atmospheric movements. On Earth. the
`boundary layer lies at the base of the *troposphere and varies in depth from a few
`hundred metres under stable conditions to 1-2 km when convection is strong.
`
`bound—bound transition A change to the energy of an electron within an atom,
`or more rarely within a molecule, in which the electron remains attached (bound) to
`the atom or molecule both before and after the change. When the energy is increased,
`a photon is absorbed; when the energy is reduced. a photon is emitted. Bound—bound
`transitions produce the emission and absorption lines found in stellar spectra.
`bound-free transition A change to the energy of an electron within an atom or a
`molecule in which the electron gains sufficient energy to escape. The electron goes
`from being bound to being free, and leaves behind an ion; hence this is another name
`for *ionization. The energy for the change may come from a photon, resulting in the
`absorption bands known as ionization edges in stellar spectra, or from collisions with
`other atoms or particles (collisional ionization). If the energy comes from another excited
`electron within the atom, the process is known as auto-ionization.
`
`Bouwers telescope A design of telescope identical to the *Maksutov telescope.
`developed by the Dutch optician Albert A. Bouwers (1893-1972). His publication of the
`design in 1940, during World War ll, predated that of the *Maksutov telescope. but
`gained little publicity because of the German occupation of Holland.
`Bowen, Ira Sprague (1898-1973) American astrophysicist. In 1927 he explained
`the origin of strong green lines in the spectra of planetary nebulae. They are
`*forbidden lines produced by transitions between atomic states in doubly ionized
`oxygen (0 III) and not, as W. *l-luggins had earlier speculated, by an unknown element
`termed ‘nebulium’. This led to the correct identification of lines in the solar specn-um
`that had been similarly attributed to a hypothetical ‘coronium‘. and thence to
`advances in the spectroscopic study of the compositions, temperatures, and densities
`of the Sun, stars, and nebulae.
`
`Bowen fluorescence A mechanism that gives rise to certain strong emission lines
`from ionized atoms of oxygen, carbon, and nitrogen in diffuse nebulae. Extremely hot
`stars and accretion disks (at temperatures of 30 000 K or more) produce copious
`amounts of extreme ultraviolet radiation at 30.4 nm from singly ionized helium atoms.
`These photons excite the ions of C III and N III in surrounding gas because the ions
`have a transition very close to this wavelength. These excited ions then return to the