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ASTRONOMYMagazineStarDomeMapbyAdolfSchaller.
Copyright C 1974byAatromediaCorp.All RightsReserved.
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ASTRONOMYMagazineStarDome MapbyAdolfSchaller.
Copyright©1975byAstromediaCorp.All RightsReserved.
Contemporary Astronomy
PASACHOFF
JAY M.
WilliamsCollege-HopkinsObservatory
Williamstown, Massachusetts
%
SAUNDERS GOLDEN SUNBURST SERIES
W. B. SAUNDERS COMPANY PHILADELPHIA / LONDON / TORONTO
\\ b Saunders Company: WestWashington Square
Philadelphia, PA 19105
E1aSsttbAonunren'es, REaosatdSussex BN21 U \, England
Goldthorne Avenue
T1oronto. Ontario M8Z 5T9, Canada
Librarj of Congress Cataloging in Publication Data
M
Pasachoff. Jay
ontemporary astronomy.
(
Includes bibliographies.
I Wronomy. 1. Title.
QB45.P29 520 76-014683
ISBN 0-7216-7101-2
Front finer illustration: Mars, a photograph from the Viking 1 spacecraft
as it approached in June 1976. The giant canyon in the upper hemisphere
lias a lamer diameter than the United States
Ba<k cover illustration: Jupiter, from the Pioneer 10 spacecraft, showing
tin- <ire.it Hed Spot.
Photographs courtesj ofN \s \
1 Astronomy ISB\ 0-7216-7101-2
( 1977 l>\ W. B. Saunders Company. Copyright under the International Copyright Union.
All rights reserved. This book is protected by copyright. No part of it may he reproduci >!
transmitted in any form orbyany means, electronic, mechanical,
photoi pi otherwise, without written permission from the publisher. Made
in the Unit Press of W. B. Saunders Company. Librar) of Congress
nd number 76-01 168
ligit is the print number:
Preface
Astronomy, as a science, combines the best of new and old traditions.
Every year we find something new or unexpected; quasars, molecules in
interstellar space, pulsars, coronal holes, x-ray bursts, black holes, and the
nature ofthe surface ofMars are but a few examples from recenttimes. Atthe
same time, astronomy has a rich and fascinating history.
I have attempted, in this book, to describe the state of astronomy as it is
now. I have tried to fit the latest discoveries in their places alongside estab-
lished results in order to give a contemporary picture of the state of our
science.
CONTEMPORARY ASTRONOMY
is written for students with no back-
ground in mathematics or physics. It discusses astronomy in non-mathemati-
cal terms. Students with mathematics or physics backgrounds, however, will
still find the book valuable because ofits unique coverage ofa wide range of
modern topics.
The book emphasizes topics that are of current interest to astronomers
and in which currentresearch is veryactive. In orderto gain space inthebook
and time in the academic year forthe contemporarymaterial, some traditional
material that is discussed at length in other texts has been minimized. But I
have attempted to cover all fields of astronomy, without major gaps.
A major theme of the book has been the expansion of our senses to all
parts of the spectrum. We see time and again through the entire book how
observations of gamma rays, x-rays, ultraviolet light, infrared light, and radio
waves are fit together with observations of visible light and with theory to
improve our knowledge ofthe universe andthe objects in it. Such new results
appear throughout the entire book, rather than being segregated in a few
chapters. Similarly, the historical side ofastronomy is also treated as the vari-
ous topics come up, rather than having historical discussions segregated.
A major goal of the book has been to describe astronomy in clear,
thorough, understandable and colloquial terms. Many discussions of espe-
cially important topics have been expanded in orderto have space to describe
various aspects. All the steps in chains of reasoning have been included in
order to make certain that the major points are clear.
An unusual aspect of CONTEMPORARY ASTRONOMY is that back-
ground discussions ofphysics andastronomyappearas theyare needed in the
text rather than as lengthy introductory chapters. This has the advantage of
making more apparent the connection between the background discussions
and the discussions ofmodern research. It has the further advantage ofallow-
ingthe student to begin with real astronomy at the very startofthe course, in-
stead ofhaving to wait until the introductory chapters are completed. Certain
background material may be briefly recapitulated in later chapters even
though it may have been dealt with more thoroughly earlier. Once again, the
iii
PREFACE
iv
son for this is to stress the connection between underlying concepts and
their applications.
In order to depict the widespread activity in astronomy, and to demon-
strate the human aspect ofastronomical research, I have sometimes named in-
dividual astronomers and institutions. Further, details that may not be im-
portant in themseh es are sometimes used to embellish the central point. The
ability to expand in this \\a\ 1ms enabled me to set main matters in especially
interesting contexts. But at no time should students find themselves memoriz-
ing material instead ofunderstanding concepts. As an aid in determiningjust
what is most important to remember, I have provided summaries of each
chapter in this book, and a detailed Student Study Guide (Pasachoff, Kutner,
and Pasachoff, Student Study Guide to CONTEMPORARY ASTRONOMY.
\\ B. Saunders Company, 1977* is also available.
.
My stress lias continually been on how to understand what is going on,
and why astronomers think or act as they do. My criterion has been to include
mostly material that can be remembered for years and that provides a basic
understanding ofthe topic, rather than facts that are merely learned for exam-
inations and then soon forgotten. In order to give a feel ofwhat it is like tobe
an astronomer, I have at several places in the text described just what an
astronomer does in different circumstances, such as observing at a large
optical or radio telescope, observing with a satellite, or working at a solar
eclipse. I have myself been fortunate to be able to observe with a variety of
optical, radio, and space telescopes in this country and abroad, and I am glad
to have the opportunity to describe the excitement an observer feels.
It also seems to me that after completing a course in astronomy a student
should be able to cany on a reasonable conversation with an astronomer.
This has led me to continue the usage ofthe somewhat strange units that are
retained by astronomers for historical reasons rather than for reasons of
logic. For example, magnitudes are used to describe the brightnesses ofstars,
though I try to make clear the relation ofthe magnitude scale to a direct scale
of brightness. Anyway, I find it easier to remember magnitudes, which are
simple numbers like 2 or 16, rather than luminosities like 2 X 104 If diese
.
units are madness, there is method in it.
I have included material meant to develop basic skills like conversion of
units; main students already have these skills and will be able to skip these
parts. (This particular skill applies as well to changing money in foreign
countries as it does to changing units in an astronomical context.) I have also
tried to bring across the importance ofestimation andrough calculation rather
than over-exact calculation based on numbers that are themselves only
roughly given or known. Of course, one is free to think that a 3rd magnitude
is (2.511887 . . .)z = 6.309573 . . . times brighter than a 5th magnitude star. I
prefer to say that it is about 6 times brighter—not because I can't do the exact
calculation (on an electronic calculator it is no harder to do than the estimate)
but because I think that the string of digits obscures the reasoning process.
The understanding of estimation and the limits ofaccurac) ran be carried b\
students into their daily lives.
In view of the importance to scientific research ofgovernmental support,
and the need for everyone to be informed about the value ofsuch research, I
have described from time to time the benefits that might accrue to society
bom
certain types of astronomical research.
Arrangement of the book
Since stars are the main point ofreference th.it most individuals have to
astronomy, I have begun my discussion with them. After discussing basic
PREFACE v
definitions and terms, I discuss the sun as a special case of a star, and then
proceed to stellar evolution, including its fascinating end-products: white
dwarfs, neutron stars (which we observe as pulsars), and black holes. I then
discuss another special case of objects closely associated with stars that we
happen to be able to study because theyare sonear: the planets. Afterthe dis-
cussions ofstars and planets, we continue outward through the universe from
small to large, with interstellar matter, our own galaxy, galaxies in general,
quasars, and then cosmological consideration ofthe universe as a whole. The
book thus describes astronomy from the inside out, beginning with the stars.
CONTEMPORARY ASTRONOMY
can be used for either a one- or two-
semester course. One topic that many professors treat in different manners is
Section III on the planets. I have placed it in this book adjacent to the dis-
cussion of stars; one could give a two-semester course with stars and planets
in the first halfandthe MilkyWay, galaxies, and cosmology in the second half.
The material in Section III on the planets could, alternatively, be taught at
other places in the syllabus or even omitted; it is not dependent on the dis-
cussions that preceded it, and neitherdo the sections thatfollow dependon it.
Some professors might want to teach the planets first; others might want to
defer the study of planets until the very end.
For aone-semesterorone-trimestersurveycourse ofall ofastronomy, one
should omit all the sections in smaller print and most of the boxes. I have
tried to construct each chapter so that the most important material appears at
the beginning, thus making itmore natural to assign onlythe firstfew sections
of the chapter and omit some of the less vital and more advanced material
that appears at the end. One possible one-semester or one-trimester course
could omit Sections 3.7 to 3.14 on observingmethods andtechniques; 4.2 and
4.3 on stellar masses and sizes, 4.5c on black holes in globularclusters; 5.2c-e
on opacity effects, 5.8 to 5.12 on secondary uses ofthe sun;6.6 onthe neutrino
experiments, 7.5 to 7.7 on relativityand novae; 8.8 to 8.12 on secondary pulsar
phenomena; 9.4 on non-stellar black holes and 9.6 on gravitational waves;
10.4 on Bodes "law"; 12.1 on the rotation ofMercury; 13.3 and 13.5 onVenus;
16.2 and 16.4 on Jupiter's moons; any or all of Chapter 18 on comets,
meteoroids, and asteroids; anyorall ofChapter 19 on life in the universe; 20.5
on spiral structure; any or all of Chapter 21 on the interstellar medium and
radio astronomy; any or all of Chapter 22 on infrared, x-ray, and gamma-ray
studies ofour galaxy; 23.2 on the origin ofgalactic structure, 23.3 on clusters
of galaxies, 23.5 on radio galaxies, and 23.6 on the formation of galaxies; 25.5
on the hierarchical universe, 25.6 and25.7 onthe creation ofthe elements and
their implications for the future ofthe universe; and any or all ofChapter 26
on how astronomical research works and on future plans and projects. This
list, obviously, can be modified substantially by individual professors. Sev-
eral alternate plans for semester or trimester courses are listed in the
Teacher's Guide.
The Student Study Guide to CONTEMPORARY ASTRONOMY, written
in collaboration with Marc L. Kutner and Naomi Pasachoff, provides a de-
tailed glossary for the terms in this book, discussions of the material in
CONTEMPORARY ASTRONOMY chapter by chapter, worked problems,
quizzes and questions, and chapter by chapter lists ofbooks and articles. In
some cases, it will be adopted for class use along with the main text; in other
cases, individual students might choose to use the book on their own.
A Teacher's Guide to CONTEMPORARYASTRONOMY is also available.
It contains problems, tests, and answers, and lists films, tapes, and other
audio and visual aids for use as supplementary material.
PREFACE
vi
We have arranged to have over220ofthe illustrations in this hook avail-
able on transparencies for overhead projection. The set includes hoth
drawings and photographs. For further information writeTextbook Marketing
Department, W. B. Saunders Company, West Washington Square, Phila-
delphia. Pa 19105.
U knowledgments
The publishers and ha\ e placed a heavy premium on accuracy, and have
I
made certain that the manuscript and proof have heen read not only by stu-
dents forclarity and stylehutalso h> se\ era! astronomers fortheirprofessional
comment. would like to thank, in particular, Thomas T. Amy (University of
I
Massachusetts at Amherst), Marc L. Kutner (Rensselaer Polytechnic In-
stitutei, Richard L. Sears (University of Michigan), and Joseph F. Veverka
Cornell University for reading the entire manuscript.
I
I would also like to thank other astronomers and physicists who have
commented on parts ofthe manuscript in their particular areas of expertise.
They include (in the approximate order in which the topics are treated in
the book
•:
fean Pierre Swings (Institut d'Astrophysique, Liege, Belgium), stars and
quasars; Jeffrey L. Linsky (Joint Institute for Laboratory Astrophysics,
Boulder), radiative transfer; David Park (Williams College), atomic physics;
Janus G. Baker (Harvard College Observatory), optics; Jonathan E. Grindlay
larvard-Smithsonian Center for Astrophysics), black holes and x-ray bursts;
I
Peter V. Foukal (Harvard-Smithsonian Center for Astrophysics), the sun;
Robert F. Howard ( 11ale ( )bsen atories), the sun; Lawrence Cram (Fraunhofer
Institute. Freiburg, German) ), opacity effects; J. CraigWheeler(University of
Texas), stellar evolution; Raymond Davis. Jr. (Brookhaven National Labora-
tory), solar neutrinos; Joseph II. Taylor, Jr. (University of Massachusetts,
Amherst), pulsars; John A. Wheeler (University of Texas), black holes; Ken-
neth Brecher (Massachusetts Institute of Technology), black holes; Peter
Conti (University of Colorado), stars; Bruce E. Bohannan (University of
Colorado), stars; Maurice Shapiro (Naval Research Laboratory), cosmic rays;
Owen Gingerich (Harvard-Smithsonian Center for Astrophysics), history
of astronomy; David D. Morrison (University of Hawaii and NASA Head-
quarters), the solar system; James P. Pollack (NASA Ames Research Center),
the solar system; Farouk El-Baz (NASA Headquarters and National Air and
Space Museum. Smithsonian Institution), the moon; Ewen A. Whitaker
lunar and Planetary Laboratory, University ofArizona), the moon; Gerald
J.
Wasserburg (California Institute of Technology), lunar chronology; William
K. Mooniaw (Williams College), ozone; Ian Halliday (Herzberg Institute of
Astrophysics, Ottawa). Neptune and Pluto; Donald Fernie (David Dunlap
J.
Observatory, Toronto), the Adams-Leverrier affair; P. Kenneth Seidel-
mann (U.S. Naval Observatory), ephemeridjes and planetarj parameters.
Brian Marsden (Harvard-Smithsonian Center for Astrophysics), comets,
asteroids, and meteoroids; George D. Gatewood (Allegheny Observaton
I,
Barnard's Star; Everett Mendelsohn (Hanaid Universit) superstition; Alan
>,
T. Moffet (California Institute ofTechnology), radio astronomy;
:is Kalnajs (Mt. Stromlo Observatory, Australia), spiral structure;
Barrj Turner (National Radio Astronomy Observatory), the latest interstellar
molecules; Juri Toomre (Joint Institute for Laboratory Astrophysics), gravita-
tional efleets on galaxies; Leonid Weliaehew (Ohservatoire de Paris. France
.\ies; George K. Mile) (LeidenObservatory,the Netherlands),interferom-
etry; Bernard J. T. Jones (Institute for Astronomy, Cambridge, England),
galaxy formation; Jerome Kristian (Hale Observatories), quasars, Seyfert and
and John Lathrop (Williams College), cosmology.
