Fundamental Astronomy

497 Pages·1987·19.556 MB·English

by  Dr. Hannu Karttunen, Dr. Pekka Kröger, Dr. Heikki Oja (auth.), Dr. Hannu Karttunen, Dr. Pekka Kröger, Dr. Heikki Oja, Dr. Markku Poutanen, Dr. Karl Johan Donner (eds.)

Fundamental Astronomy
Editors: H. Karttunen, P. Kröger,
H. Oja, M. Poutanen, and K.J. Donner

tal
Editors: H. Karttunen, P. Kröger,
H. Oja, M. Poutanen, and K.J. Donner
With 399 Illustrations Inc1uding 36 Colour Plates
Springer-Verlag New York Berlin Heidelberg
London Paris Tokyo Hong Kong Barcelona
Drs. Hannu Karttunen . Pekka Kröger
Drs. Heikki Oja . Markku Poutanen . Karl Johan Donner
University of Helsinki, Observatory and Astrophysics Laboratory, Tähtitorninmäki
SF-00130 Helsinki 13, Finland
Cover photograph: Dome of the European Southern Observatory 3.6m telescope at
La Silla, Chile. (Photograph European Southern Observatory)
Frontispiece: The YJ Carinae nebula, NGC3372, is a giant HII region in the Carina spiral
arm of our galaxy at a distance of 8000 light-years. (Photograph European Southern
Observatory)
Title of the original Finnish edition: Tähtitieteen perusteet (Ursan julkaisuja 21)
© Tähtitieteellinen yhdistys Ursa, Helsinki 1984
Sources for the illustrations are given in the captions and more fully at the end of the book. Most of the
uncredited illustrations are
© Ursa Astronomical Association, Laivanvarustajank 3, SF-00140 Helsinki, Finland
ISBN 978-0-387-97567-2 ISBN 978-1-4612-3160-8 (eBook)
DOI 10.1007/978-1-4612-3160-8
Library of Congress Cataloging-in-Publication Data. Fundamental astronomy. Bibliography: p. Includes index.
1. Astronomy. 1. Karttunen, Hannu. QB43.2.F86 1987 520 86-31492
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© Springer-Verlag Berlin Heidelberg 1987
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Typesetting: K + V Fotosatz, 6124 Beerfelden
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Preface
The main purpose of this book is to serve as a university textbook for a first course in
astronomy. However, we believe that the audience will also include many serious ama
teurs, who often find the popular texts too trivial. The lack of a good handbook for am
ateurs has become a problem lately, as more and more people are buying personal com
puters and need exact, but comprehensible, mathematical formalism for their programs.
The reader of this book is assumed to have only a standard high-school knowledge of
mathematics and physics (as they are taught in Finland); everything more advanced is
usually derived step by step from simple basic principles. The mathematical background
needed includes plane trigonometry, basic differential and integral calculus, and (only in
the chapter dealing with celestial mechanics) some vector calculus. Some mathematical
concepts the reader may not be familiar with are briefly explained in the appendices or
can be understood by studying the numerous exercises and examples. However, most of
the book can be read with very little knowledge of mathematics, and even if the reader
skips the mathematically more involved sections, (s)he should get a good overview of the
field of astronomy.
This book has evolved in the course of many years and through the work of several
authors and editors. The first version consisted of lecture notes by one of the editors (Oja).
These were later modified and augmented by the other editors and authors. Hannu Kart
tunen wrote the chapters on spherical astronomy and celestial mechanics; Vilppu Piirola
added parts to the chapter on observational instruments, and Göran Sandell wrote the part
about radio astronomy; chapters on magnitudes, radiation mechanisms and temperature
were rewritten by the editors; Markku Poutanen wrote the chapter on the solar system;
Juhani Kyröläinen expanded the chapter on stellar spectra; Timo Rahunen rewrote most
of the chapters on stellar structure and evolution; Ilkka Tuominen revised the chapter on
the Sun; Kalevi Mattila wrote the chapter on interstellar matter; Tapio Markkanen wrote
the chapters on star clusters and the Milky Way; Karl Johan Donner wrote the major part
of the chapter on galaxies; Mauri Valtonen wrote parts of the galaxy chapter, and, in col
laboration with Pekka Teerikorpi, the chapter on cosmology. Finally, the resulting, some
what inhomogeneous, material was made consistent by the editors.
The English text was written by the editors, who translated parts of the original Finnish
text, and rewrote other parts, updating the text and correcting errors found in the original
edition. The parts of text set in smaller print are less important material that may still be of
interest to the reader.
For the illustrations, we received help from Veikko Sinkkonen, Mirva Vuori and sever
al observatories and individuals mentioned in the figure captions. In the practical work, we
were assisted by Arja Kyröläinen and Merja Karsma. Apart of the translation was read
and corrected by Brian Skiff. We want to express our warrnest thanks to all of them.
Financial support was given by the Finnish Ministry of Education and Suomalaisen kir
jallisuuden edistämisvarojen valtuuskunta (a foundation promoting Finnish literature), to
whom we express our gratitude.
Helsinki, June 1987 TheEditors
Contents
1. Introduetion...................................................... 1
1.1 The Role of Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Astronomical Objects of Research. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 The Scale of the Uni verse ...................................... 4
2. Spherieal Astronomy .............................................. 9
2.1 Spherical Trigonometry ....................................... 9
2.2 The Earth ................................................... 13
2.3 The Celestial Sphere .......................................... 15
2.4 The Horizontal System ........................................ 15
2.5 The Equatorial System ........................................ 17
2.6 The Ecliptic System ........................................... 22
2.7 The Galactic Coordinates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.8 Perturbations of Coordinates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.9 Constellations................................................ 28
2.10 Star Catalogues and Maps ..................................... 29
2.11 Positional Astronomy ......................................... 32
2.12 Time Reckoning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.13 Astronomical Time Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.14 Calendars ................................................... 39
2.15 Exercises .................................................... 42
3. Observations and Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.1 Observing Through the Atmosphere ............................. 47
3.2 Optical Telescopes ............................................ 50
3.3 Detectors.................................................... 64
3.4 Radio Telescopes ............................................. 69
3.5 Other Wavelength Regions ..................................... 76
3.6 Instruments ofthe Future. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.7 Other Forms ofEnergy ........................................ 83
3.8 Exercises.................................................... 85
4. Photometrie Coneepts and Magnitudes ............................... 87
4.1 Intensity, Flux Density and Luminosity .......................... 87
4.2 Apparent Magnitudes ......................................... 91
4.3 Magnitude Systems ........................................... 92
4.4 Absolute Magnitudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.5 Extinction and Optical Thickness ............................... 95
4.6 Exercises.................................................... 98
5. Radiation Meehanisms ............................................. 103
5.1 Radiation of Atoms and Molecules .............................. 103
VIII Contents
5.2 The Hydrogen Atom .......................................... 105
5.3 Quantum Numbers, Selection Rules, Population Numbers .......... 109
5.4 Molecular Spectra ............................................ 110
5.5 Continuous Spectra ........................................... 110
5.6 Blackbody Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.7 Other Radiation Mechanisms .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
5.8 Radiative Transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
5.9 Exercises.................................................... 118
6. Temperatures..................................................... 119
6.1 Exercises.................................................... 122
7. Celestial Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
7.1 Equations ofMotion .......................................... 123
7.2 Solution ofthe Equation of Motion ............................. 124
7.3 Equation of the Orbit and Kepler's First Law ..................... 128
7.4 Orbital Elements ............................................. 129
7.5 Kepler'sSecondandThirdLaw ................................. 131
7.6 Orbit Determination .......................................... 134
7.7 Position in the Orbit .......................................... 134
7.8 Escape Velocity .............................................. 136
7.9 Virial Theorem .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
7.10 The Jeans Limit .............................................. 140
7.11 Exercises .................................................... 142
8. The Solar System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
8.1 An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 147
8.2 Planetary Configurations ...................................... 148
8.3 OrbitoftheEarth ............................................ 150
8.4 Orbit ofthe Moon ............................................ 152
8.5 Eclipses and Occultations ...................................... 154
8.6 Albedos ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
8.7 Planetary Photometry, Polarimetry and Spectroscopy . . . . . . . . . . . . . . 158
8.8 Thermal Radiation ofthe Planets ............................... 162
8.9 The Structure of Planets ....................................... 164
8.10 Planetary Surfaces ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
8.11 Atmospheres and Magnetospheres .............................. 168
8.12 Mercury ... . ... ... . ... ... .... ... . ... .... ... ...... .... . .... . .. 172
8.13 Venus ............................................... '" . .... 174
8.14 The Earth and the Moon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 177
8.15 Mars ....................................................... 183
8.16 Asteroids .. ...... . ... ... . ... .... .... .. . ... ... ... . ... .... . .... 187
8.17 Jupiter .. , ............................ '" ........... '" ... , .. 189
8.18 Saturn ...................................................... 194
8.19 Uranus, Neptune and Pluto .................................... 197
8.20 Minor Bodies ofthe Solar System ............................... 202
8.21 Cosmogony.................................................. 205
8.22 Other Solar Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 209
8.23 Exercises .................................................... 210
Contents IX
9. Stellar Spectra .................................................... 215
9.1 Measuring Speetra ............................................ 215
9.2 The Harvard Speetral Classifieation ............................. 218
9.3 The Yerkes Speetral Classifieation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 221
9.4 Peeuliar Speetra .............................................. 223
9.5 The Hertzsprung-Russell Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
9.6 Model Atmospheres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 226
9.7 What Do the Observations Tell Us? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 227
10. Binary Stars and Stellar Masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
10.1 Visual Binaries ............................................... 232
10.2 Astrometrie Binary Stars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
10.3 Speetroseopie Binaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
10.4 Photometrie Binary Stars ...................................... 235
10.5 Exercises .................................................... 237
11. Stellar Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 241
11.1 Internal Equilibrium Conditions ................................ 241
11.2 Physieal State of the Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
11.3 Stellar Energy Sourees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 249
11.4 Stellar Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
11.5 Exercises .................................................... 255
12. Stellar Evolution .................................................. 259
12.1 Evolutionary Time Seales ...................................... 259
12.2 The Contraetion of Stars Towards the Main Sequenee .............. 260
12.3 The Main Sequenee Phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 262
12.4 The Giant Phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
12.5 The Final Stages ofEvolution .................................. 267
12.6 The Evolution of Close Binary Stars ............................. 270
12.7 Comparison with Observations ................................. 272
12.8 The Origin ofthe Elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 273
13. The Sun ......................................................... 277
13.1 Internal Strueture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 277
13.2 The Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 279
13.3 Solar Aetivity ................................................ 283
14. Variable Stars .................................................... 291
14.1 Classifieation ................................................ 292
14.2 Pulsating Variables ........................................... 293
14.3 Eruptive Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 296
14.4 Exercises .................................................... 303
15. Compact Stars .................................................... 305
15.1 White Dwarfs ................................................ 305
15.2 Neutron Stars ................................................ 306
15.3 Blaek Holes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
x Contents
16. The Interstellar Medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 317
16.1 Interstellar Dust ............................................. 317
16.2 Interstellar Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 329
16.3 Interstellar Moleeules ........................................ 337
16.4 The Formation of Protostars .................................. 341
16.5 Planetary Nebulae ........................................... 342
16.6 Supernova Remnants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 343
16.7 The Hot Corona ofthe Milky Way ............................. 346
16.8 Cosmie Rays and the Interstellar Magnetie Field .................. 347
17. Star Clusters and Associations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
17.1 Associations................................................ 350
17.2 Open Star Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 351
17.3 Globular Star Clusters.. .. . . ... .... . ... ... ... . .. ... .... .... . .. 354
18. The Milky Way ................................................... 357
18.1 MethodsofDistaneeMeasurement ............................. 359
18.2 Stellar Statisties ............................................. 362
18.3 TheRotationoftheMilkyWay................................ 367
18.4 The Strueture and Evolution ofthe Milky Way ................... 374
18.5 Exercises................................................... 377
19. Galaxies ......................................................... 379
19.1 TheClassifieationofGalaxies ................................. 379
19.2 Elliptieal Galaxies ........................................... 381
19.3 Spiral Galaxies .............................................. 388
19.4 Lentieular Galaxies .......................................... 392
19.5 Luminosities ofGalaxies .. , ............ , ........ " ...... , . .... 392
19.6 Masses of Galaxies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 393
19.7 Systems of Galaxies .......................................... 395
19.8 Distanees of Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
19.9 Aetive Galaxies and Quasars .................................. 398
19.10 The Origin and Evolution of Galaxies. . . . . . . . . . . . . . . . . . . . . . . . . .. 403
20. Cosmology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 405
20.1 CosmologiealObservations ................................... 405
20.2 The Cosmologieal Principle ................................... 412
20.3 Homogeneous and Isotropie Universes . . . . . . . . . . . . . . . . . . . . . . . . .. 414
20.4 The Friedmann Models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 416
20.5 Cosmologieal Tests .......................................... 421
20.6 History ofthe Universe ....................................... 423
20.7 The Future ofthe Uni verse .................................... 426
Appendices ..................................................... 429
A. Mathematies ..................................................... 429
A.1 Geometry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
A.2 Taylor Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
A.3 Veetor Calculus ............................................. 431
A.4 Conie Seetions .............................................. 433
Contents XI
A.5 Multiple Integrals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 434
A.6 Numerical Solution of an Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 435
B. Quantum Mechanics .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
B.1 Quantum Mechanical Model of Atoms. Quantum Numbers ......... 437
B.2 Selection Rules and Transition Probabilities ...................... 438
B.3 Heisenberg's Uncertainty Principle .............................. 438
BA Exclusion Principle ........................................... 439
C. Theory of Relativity ............................................... 439
C.1 Basic Concepts ............................................... 439
C.2 Lorentz Transformation. Minkowski Space . . . . . . . . . . . . . . . . . . . . . . . 441
C.3 General Relativity ............................................ 442
CA Tests of General Relativity ..................................... 443
D. Radio Astronomy Fundamentals .................................... 444
D.1 Antenna Definitions .......................................... 444
D.2 Antenna Temperature and Flux Density .......................... 446
E. Tables........................................................... 447
Further Reading ...................................................... 465
Photograph Credits ................................................... 469
Subject Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 471