1、DICTIONARY OFGEOPHYSICS,ASTROPHYSICS,andASTRONOMY 2001 by CRC Press LLC Comprehensive Dictionaryof PhysicsDipak BasuEditor-in-ChiefPUBLISHED VOLUMESDictionary of Pure and Applied PhysicsDipak BasuDictionary of Material Scienceand High Energy PhysicsDipak BasuDictionary of Geophysics, Astrophysics,an
2、d AstronomyRichard A. Matzner 2001 by CRC Press LLC a Volume in theComprehensive Dictionaryof PHYSICSDICTIONARY OFGEOPHYSICS,ASTROPHYSICS,andASTRONOMYEdited byRichard A. MatznerBoca Raton London New York Washington, D.C.CRC Press 2001 by CRC Press LLC This book contains information obtained from aut
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9、 Number 0-8493-2891-8Library of Congress Card Number 2001025764Printed in the United States of America 1 2 3 4 5 6 7 8 9 0Printed on acid-free paperLibrary of Congress Cataloging-in-Publication DataDictionary of geophysics, astrophysics, and astronomy / edited by Richard A. Matzner.p. cm. (Comprehen
10、sive dictionary of physics)ISBN 0-8493-2891-8 (alk. paper)1. AstronomyDictionaries. 2. GeophysicsDictionaries. I. Matzner, Richard A.(Richard Alfred), 1942- II. Series.QB14 .D53 2001520.3dc21 20010257642891 disclaimer Page 1 Friday, April 6, 2001 3:46 PMPREFACEThis work is the result of contribution
11、s from 52 active researchers in geophysics, astrophysicsand astronomy. We have followed a philosophy of directness and simplicity, while still allowingcontributors flexibility to expand in their own areas of expertise. They are cited in the contributorslist, but I take this opportunity to thank the
12、contributors for their efforts and their patience.The subject areas of this dictionary at the time of this writing are among the most active of thephysical sciences. Astrophysics and astronomy are enjoying a new golden era, with remarkableobservations in new wave bands (-rays, X-rays, infrared, radi
13、o) and in new fields: neutrino and(soon) gravitational wave astronomy. High resolution mapping of planets continuously yields newdiscoveries in the history and the environment of the solar system. Theoretical developments arematching these observational results, with new understandings from the larg
14、est cosmological scale tothe interior of the planets. Geophysics mirrors and drives this research in its study of our own planet,and the analogies it finds in other solar system bodies. Climate change (atmospheric and oceaniclong-timescale dynamics) is a transcendingly important societal, as well as
15、 scientific, issue. Thisdictionary provides the background and context for development for decades to come in these andrelated fields. It is our hope that this dictionary will be of use to students and established researchersalike.It is a pleasure to acknowledge the assistance of Dr. Helen Nelson, a
16、nd later, Ms. Colleen McMil-lon, in the construction of this work. Finally, I acknowledge the debt I owe to Dr. C.F. Keller, and tothe late Prof. Dennis Sciama, who so broadened my horizons in the subjects of this dictionary.Richard MatznerAustin, Texas 2001 by CRC Press LLC CONTRIBUTORSTokuhide Aka
17、baneKyoto UniversityJapanDavid AlexanderLockheed Martin Solar also called optical density.absorptance The fraction of the incidentpower at a given wavelength that is absorbedwithin a volume.absorption coefficient The absorptance perunit distance of photon travel in a medium, i.e.,the limit of the ra
18、tio of the spectral absorptanceto the distance of photon travel as that distancebecomes vanishingly small. Units: m1.absorption cross-section The cross-section-al area of a beam containing power equal to thepower absorbed by a particle in the beam m2.absorption efficiency factor The ratio ofthe abso
19、rption cross-section to the geometricalcross-section of the particle.absorption fading In radio communication,fading is caused by changes in absorption thatcause changes in the received signal strength. Ashort-wave fadeout is an obvious example, andthe fade, in this case, may last for an hour ormore
20、. See ionospheric absorption, short wavefadeout.absorption line A dark line at a particu-lar wavelength in the spectrum of electromag-netic radiation that has traversed an absorbingmedium (typically a cool, tenuous gas between ahot radiating source and the observer). Absorp-tion lines are produced b
21、y a quantum transitionin matter that absorbs radiation at certain wave-lengths and produces a decrease in the intensityaround those wavelengths. See spectrum. Com-pare with emission line.abstract index notation A notation of ten-sors in terms of their component index structure(introduced by R. Penro
22、se). For example, thetensor T(,)= Tbaabis written in theabstract index notation asTba, where the indicessignify the valence and should not be assigneda numerical value. When components need tobe referred to, these may be enclosed in matrixbrackets: (va)=(v1,v2).abyssal circulation Currents in the oc
23、eanthat reach the vicinity of the sea floor. Whilethe general circulation of the oceans is primarilydriven by winds, abyssal circulation is mainly 2001 by CRC Press LLC accretion diskdriven by density differences caused by temper-ature and salinity variations, i.e., the thermoha-line circulation, an
24、d consequently is much moresluggish.abyssal plain Deep old ocean floor coveredwith sediments so that it is smooth.acceleration The rate of change of the veloc-ity of an object per unit of time (in Newtonianphysics) and per unit of proper time of the object(in relativity theory). In relativity, accel
25、erationalso has a geometric interpretation. An objectthat experiences only gravitational forces movesalong a geodesic in a spacetime, and its accel-eration is zero. If non-gravitational forces actas well (e.g., electromagnetic forces or pressuregradient in a gas or fluid), then acceleration atpointp
26、 in the spacetime measures the rate withwhich the trajectoryC of the object curves offthe geodesic that passes throughp and is tan-gent toC atp. In metric units, acceleration hasunits cm/sec2 ; m/sec2.acceleration due to gravity (g) The standardvalue(9.80665m/s2) of the acceleration experi-enced by
27、a body in the Earths gravitational field.accreted terrain A terrain that has been ac-creted to a continent. The margins of many con-tinents, including the western U.S., are made upof accreted terrains. If, due to continental drift,New Zealand collides with Australia, it wouldbe an accreted terrain.a
28、ccretion The infall of matter onto a body,such as a planet, a forming star, or a black hole,occurring because of their mutual gravitationalattraction. Accretion is essential in the forma-tion of stars and planetary systems. It is thoughtto be an important factor in the evolution of starsbelonging to
29、 binary systems, since matter can betransferredfromonestartoanother, andinactivegalactic nuclei, where the extraction of gravita-tional potential energy from material which ac-cretes onto a massive black hole is reputed to bethe source of energy. The efficiency at whichgravitational potential energy
30、 can be extracteddecreases with the radius of the accreting bodyand increases with its mass. Accretion as an en-ergy source is therefore most efficient for verycompact bodies like neutron stars (R 10 km)or black holes; in these cases, the efficiency canbe higher than that of thermonuclear reactions.
31、Maximum efficiency can be achieved in the caseof a rotating black hole; up to 30% of the restenergy of the infalling matter can be convertedinto radiating energy. If the infalling matter hassubstantial angular momentum, then the processof accretion progresses via the formation of anaccretion disk, w
32、here viscosity forces cause lossof angular momentum, and lets matter drift to-ward the attracting body.In planetary systems, the formation of largebodies by the accumulation of smaller bodies.Most of the planets (and probably many of thelarger moons) in our solar system are believedto have formed by
33、 accretion (Jupiter and Sat-urn are exceptions). As small objects solidifiedfrom the solar nebula, they collided and occa-sionally stuck together, forming a more massiveobject with a larger amount of gravitational at-traction. This stronger gravity allowed the ob-ject to pull in smaller objects, gra
34、dually build-ing the body up to a planetismal (a few kilo-meters to a few tens of kilometers in diameter),then a protoplanet (a few tens of kilometers upto 2000 kilometers in diameter), and finally aplanet (over 2000 kilometers in diameter). Seeaccretion disk, active galactic nuclei, black hole,quas
35、i stellar object, solar system formation, starformation, X-ray source.accretionary prism (accretionary wedge)The wedge-shaped geological complex at thefrontal portion of the upper plate of a subductionzone formed by sediments scraped off the top ofthe subducting oceanic plate. The sediments un-dergo
36、 a process of deformation, consolidation,diagenesis, and sometimes metamorphism. Thewedge partially or completely fills the trench.The most frontal point is called the toe or defor-mation front. See trench.accretion disk A disk of gas orbiting a ce-lestial body, formed by inflowing or accretingmatte
37、r. In binary systems, if the stars are suffi-ciently close to each other so that one of the starsis filling its Roche Lobe, mass will be transferredto the companion star creating an accretion disk.In active galactic nuclei, hot accretion diskssurround a supermassive black hole, whose 2001 by CRC Pre
38、ss LLC accretion, Eddingtonpresenceispartofthe“standardmodel”ofactivegalactic nuclei, and whose observational statusis becoming secure. Active galactic nuclei arethought to be powered by the release of poten-tial gravitational energy by accretion of matteronto a supermassive black hole. The accretio
39、ndisk dissipates part of the gravitational poten-tial energy, and removes the angular momen-tum of the infalling gas. The gas drifts slowlytoward the central black hole. During this pro-cess, the innermost annuli of the disk are heatedto high temperature by viscous forces, and emita “stretched therm
40、al continuum”, i.e., the sumof thermal continua emitted by annuli at differ-ent temperatures. This view is probably validonly in active galactic nuclei radiating below theEddington luminosity, i.e., low luminosity ac-tive galactic nuclei like Seyfert galaxies. If theaccretion rate exceeds the Edding
41、ton limit, thedisk may puff up and become a thick torus sup-ported by radiation pressure. The observationalproof of the presence of accretion disks in ac-tive galactic nuclei rests mainly on the detectionof a thermal feature in the continuum spectrum(the big blue bump), roughly in agreement withthe
42、predictions of accretion disk models. Sincethe disk size is probably less than 1 pc, the diskemitting region cannot be resolved with present-day instruments. See accretion, active galacticnuclei, big blue bump, black hole, Eddingtonlimit.accretion, Eddington As material accretesonto a compact object
43、 (neutron star, black hole,etc.), potential energy is released. The Edding-ton rate is the critical accretion rate where therate of energy released is equal to the Eddingtonluminosity: GMEddingtonMaccretor/Raccretor=LEddington Maccretion =4cRaccreting objectwhere is the opacity of the material in un
44、itsof area per unit mass. For spherically sym-metric accretion where all of the potential en-ergy is converted into photons, this rate is themaximum accretion rate allowed onto the com-pact object (see Eddington luminosity). Forionized hydrogen accreting onto a neutron star(RNS = 10 kmM NS = 1.4Mcir
45、cledot), this rate is:1.5 10 8Mcircledot yr1. See also accretion, Super-Eddington.accretion, hypercritical See accretion,Super-Eddington.accretion, Super-Eddington Mass accretionat a rate above the Eddington accretion limit.These rates can occur in a variety of accretionconditions such as: (a) in bl
46、ack hole accretionwhere the accretion energy is carried into theblack hole, (b) in disk accretion where luminos-ity along the disk axis does not affect the accre-tion, and (c) for high accretion rates that createsufficiently high densities and temperatures thatthe potential energy is converted into
47、neutrinosrather than photons. In this latter case, due tothe low neutrino cross-section, the neutrinos ra-diate the energy without imparting momentumonto the accreting material. (Syn. hypercriticalaccretion).Achilles A Trojan asteroid orbiting at the L4point in Jupiters orbit (60ahead of Jupiter).ac
48、hondrite A form of igneous stony mete-orite characterized by thermal processing andthe absence of chondrules. Achondrites are gen-erally of basaltic composition and are furtherclassified on the basis of abundance variations.Diogenites contain mostly pyroxene, while eu-crites are composed of plagiocl
49、ase-pyroxenebasalts. Ureilites have small diamond inclu-sions. Howardites appear to be a mixture of eu-crites and diogenites. Evidence from microme-teorite craters, high energy particle tracks, andgas content indicates that they were formed onthe surface of a meteorite parent body.achromatic objective The compound objec-tive lens (front lens) of a telescope or other op-tical instrument which is specially designed tominimize chromatic aberation. This objectiveconsists of two lenses, one converging and theother diverging; either glued to
