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Astrophysics: Decoding the Cosmos

Astrophysics: Decoding the Cosmos

Judith Ann Irwin

ISBN: 978-0-470-01306-9

Jun 2007

446 pages

In Stock



Astrophysics: Decoding the Cosmos is an accessible introduction to the key principles and theories underlying astrophysics.

This text takes a close look at the radiation and particles that we receive from astronomical objects, providing a thorough understanding of what this tells us, drawing the information together using examples to illustrate the process of astrophysics. Chapters dedicated to objects showing complex processes are written in an accessible manner and pull relevant background information together to put the subject firmly into context.

The intention of the author is that the book will be a ‘tool chest’ for undergraduate astronomers wanting to know the how of astrophysics. Students will gain a thorough grasp of the key principles, ensuring that this often-difficult subject becomes more accessible.

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Appendix: dimensions, units and equations.


1 Defining the signal.

1.1 The power of light - luminosity and spectral power.

1.2 Light through a surface - flux and flux density.

1.3 The brightness of light - intensity and specific intensity.

1.4 Light from all angles - energy density and mean intensity.

1.5 How light pushes - radiation pressure.

1.6 The human perception of light - magnitudes.

1.7 Light aligned - polarization.


2 Measuring the signal.

2.1 Spectral filters and the panchromatic universe.

2.2 Catching the signal – the telescope.

2.3 The Corrupted signal – the atmosphere.

2.4 Processing the signal.

2.5 Analysing the signal.

2.6 Visualizing the signal.


Appendix: refraction in the Earth’s atmosphere.


3 Matter essentials.

3.1 The Big Bang.

3.2 Dark and light matter.

3.3 Abundances of the elements.

3.4 The gaseous universe.

3.5 The dusty Universe.

3.6 Cosmic rays.


Appendix: the electron/proton ratio in cosmic rays.

4 Radiation essentials.

4.1 Black body radiation.

4.2 Grey bodies and planetary temperatures.


Appendix: derivation of the Planck function.

4.A.1 The statistical weight.

4.A.2 The mean energy per state.

4.A.3 The specific energy density and specific intensity.


5 The interaction of light with matter.

5.1 The photon redirected – scattering.

5.2 The photon lost – absorption.

5.3 The wavefront redirected – refraction.

5.4 Quantifying opacity and transparency.

5.5 The opacity of dust – extinction.


6 The signal transferred.

6.1 Types of energy transfer.

6.2 The equation of transfer.

6.3 Solutions to the equation of transfer.

6.4 Implications of the LTE solution.


7 The interaction of light with space.

7.1 Space and time.

7.2 Redshifts and blueshifts.

7.3 Gravitational refraction.

7.4 Time variability and source size.



8 Continuum emission.

8.1 Characteristics of continuum emission – thermal and non-thermal.

8.2 Bremsstrahlung (free–free) emission.

8.3 Free–bound (recombination) emission.

8.4 Two-photon emission.

8.5 Synchrotron (and cyclotron) radiation.

8.5.4 Synchrotron sources – spurs, bubbles, jets, lobes and relics.

8.6 Inverse Compton radiation.


9 Line emission.

9.1 The richness of the spectrum – radio waves to gamma rays.

9.2 The line strengths, thermalization, and the critical gas density.

9.3 Line broadening.

9.4 Probing physical conditions via electronic transitions.

9.5 Probing physical conditions via molecular transitions.



10 Forensic astronomy.

10.1 Complex spectra.

10.2 Case studies – the active, the young, and the old.

10.3 The messenger and the message.


Appendix A: Mathematical and geometrical relations.

A.1 Taylor series.

A.2 Binomial expansion.

A.3 Exponential expansion.

A.4 Convolution.

A.5 Properties of the ellipse.

Appendix B: Astronomical geometry.

B.1 One-dimensional and two-dimensional angles.

B.2 Solid angle and the spherical coordinate system.

Appendix C: The hydrogen atom.

C.1 The hydrogen spectrum and principal quantum number.

C.2 Quantum numbers, degeneracy, and statistical weight.

C.3 Fine structure and the Zeeman effect.

C.4 The l 21 cm line of neutral hydrogen.

Appendix D: Scattering processes.

D.1 Elastic, or coherent scattering.

D.1.1 Scattering from free electrons – Thomson scattering.

D.1.2 Scattering from bound electrons I: the oscillator model.

D.1.3 Scattering from bound electrons II: quantum mechanics.

D.1.4 Scattering from bound electrons III: resonance scattering and the natural line shape.

D.1.5 Scattering from bound electrons IV: Rayleigh scattering.

D.2 Inelastic scattering – Compton scattering from free electrons.

D.3 Scattering by dust.

Appendix E: Plasmas, the plasma frequency, and plasma waves.

Appendix F: The Hubble relation and the expanding Universe.

F.1 Kinematics of the Universe.

F.2 Dynamics of the Universe.

F.3 Kinematics, dynamics and high redshifts.

Appendix G: Tables and Figures.



"This is a very easy to read textbook although full of physical insight. I would certainly recommend undergraduate students to take a good look at it." (The Higher Education Academy Physical Sciences Centre, June 2008)

"Good upper-level physics students…graduate students will cherish this book..." (CHOICE, January 2008)

  • An accessible student-friendly guide to the key theories and principles of astrophysics
  • Includes numerous illustrations and examples to enhance student understanding
  • Focuses on the how of astronomy- how densities, temperatures, masses, energies are actually determined
  • Each chapter focuses on a physical process that is illustrated with relevant examples and shows how the information we receive either in particles or waves provides us with an understanding of the astronomical object
  • Key background information is provided putting the subject firmly into context
  • Gives the physics first and moves on to provide examples of the theory in practice
  • Includes further reading and problems at the end of each chapter.