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Why the Sky is Blue: Discovering the Color of Life

Götz Hoeppe
Princeton University Press
Publication Date: 
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[Reviewed by
Sarah Boslaugh
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“Why is the sky blue?” must be one of the most common questions ever posed by mankind: and anyone with children has probably fielded it more than once, and scholars have been seeking the answer since ancient times. Although this question may be asked by a child, however, the answer proves to be far from obvious. In fact, this seemingly simple question contains within itself many more questions, such as “what do you mean by blue?” “how do our eyes (and brain) perceive color?” “what has the color blue meant in different cultures?” “what causes the gradations we observe in the sky’s color?” and “how can the sky remain blue after the sun has set?”.

Götz Hoeppe has an unusual background for a science writer, since he studied both hard sciences and ethnology and has published a previous book based on fieldwork among fisherman in Kerala, India. The breadth of his knowledge is evident in Why the Sky is Blue, which is as concerned with the historical and cultural contexts in which this question was examined as it is in the theories generated and tested to answer it. Hoeppe casts his net wide, with ample inclusion of contributions from outside Europe: among the various artists, philosophers and scientists whose theories are discussed in Why the Sky is Blue are Aristotle, Abus Yusuf Ya’qub Ibn Ishaq al Kindi, Ali al-Hasan Ibn al-Haytham, Roger Bacon, Leon Battista Alberti, Leonardo da Vinci, Isaac Newton, Alexander von Humboldt, Johann Wolfgang von Goethe, John William Strutt (Lord Rayleigh), Chandrasekhara Venkata Raman, and Edward Olson Hulburt.

Why the Sky is Blue is fascinating reading, taking the reader on a scientific and historical journey from the ancient Greece to the present-day, from nomads in the desert to modern scientists in the lab. Hoeppe has the gift of presenting massive quantities of information with a light touch but without cheapening the tone of his text. For instance, in describing investigations into the chameleon’s ability to change the color of its skin, he remarks that the scientists of the Imperial Academy of Sciences in Vienna placed an order in 1851 for 10 chameleons with one Dr. Lautner, a corresponding member of the academy “known as a reliable procurer of flies, spiders, and parasites from the Egyptian desert.” (p. 131) The main story can be easily followed even by readers without a strong physics background, while technical explanations are provider for the more scientifically-minded. The text is amply illustrated with a number of diagrams and tables, including 24 beautiful color plates.

Götz Hoeppe studied physics, astronomy and ethnology in Göttingen, Albuquerque and Berlin and has done fieldword in Papua New Guinea and India. He is an editor of Spektrum der Wissenschaf, a popular German science magazine, and is a lecturer in social anthropology at Heidelberg University. He has also written Conversations on the Beach: Fishermen’s Knowledge, Metaphor and Environmental Change in South India (Berghahn Books, 2006).

Sarah Boslaugh ( is a Performance Review Analyst for BJC HealthCare and an Adjunct Instructor in the Washington University School of Medicine, both in St. Louis, MO. Her books include An Intermediate Guide to SPSS Programming: Using Syntax for Data Management (Sage, 2004), Secondary Data Sources for Public Health: A Practical Guide (Cambridge, 2007), and Statistics in a Nutshell (O'Reilly, forthcoming), and she is Editor-in-Chief of The Encyclopedia of Epidemiology (Sage, forthcoming).

 List of Illustrations ix
List of Tables xvii
Acknowledgments xix
Prologue: Looking at the Sky 1
Chapter 1: Of Philosophers and the Color Blue 9
Chapter 2: A Blue Mixture: Light and Darkness 31
Chapter 3: Aerial Perspective 52
Chapter 4: A Color of the First Order 77
Chapter 5: Basic Phenomenon, or Optical Illusion? 108
Chapter 6: A Polarized Sky 131
Chapter 7: Lord Rayleigh's Scattering 169
Chapter 8: Molecular Reality 203
Chapter 9: Ozone's Blue Hour 235
Chapter 10: The Color of Life 261
Epilogue 289
Appendix A: Determining the Height of the Atmosphere from the Duration of Twilight 291
Appendix B: Blue Eyes as Turbid Media 293
Appendix C: A Simple Derivation of the Inverse Fourth Power Law 295
Appendix D: Atmospheric Extinction and Avogadro's Number 297
Notes 299
Further Reading 311
Index 325