Why is the sky blue?
Parents don't know what to say when their children ask.
Why the Sky is Blue answers this ancient and surprisingly complex question in a more entertaining and accessible way than ever before. Götz Hoeppe takes the reader on a historical and scientific journey to show the various ways people in different times and places have explained why the sky looks blue. The richly illustrated story begins with ancient myths and philosophy and ends with the cutting-edge science of optics, statistical physics, and ozone depletion. Most importantly, it is the story of how scientists discovered that the sky's blue depends on life on Earth and the makeup of our planet's ozone layer. Without microbial life's impact on the composition of the atmosphere, the clear daytime sky would probably lack its distinctive color. And without the ozone, the twilight sky's color would also be very different – not the sapphire tone of l'heure bleue, but rather a yellowish or greenish hue.
Why the Sky is Blue shows that skylight can be viewed from a surprising variety of vantage points. We learn how our physiology and cognitive capacities govern our perception of the sky's color. And we discover why this everyday experience has been such a source of fascination and controversy over the centuries.
Delightful and intriguing, Why the Sky is Blue shows how the attempt to answer this age-old and deceptively simple question only enhances the magic of the blue sky we see above us.
List of Illustrations ix
List of Tables xvii
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
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
Further Reading 311
Götz Hoeppe is an editor of the popular German science magazine Spektrum der Wissenschaft and a lecturer in social anthropology at Heidelberg University. He is the author of Conversations on the Beach: Fishermen's Knowledge, Metaphor and Environmental Change in South India.
"As Götz Hoeppe's excellent history of our attempts to explain the blue of the sky shows, from moments of wonder [...] scientific theories grow [...] A thorough and detailed history."
– P. D. Smith, Times Literary Supplement
"Delivering far more than the title promises, Hoeppe's book describes an intellectual quest that began with the ancients. He details our growing understanding of the sky's light, and the insights and experiments that brought it about [...] A well-illustrated, rewarding read."
– Jon Richfield, New Scientist
"Hoeppe offers accessible insights into a question that extends well beyond the realm of science."
"This book could as easily have been titled 'Is the Sky Blue?' And the answer to that is yes and no [...] One of the interesting things about Why the Sky is Blue is that as a German, Hoeppe spreads credit for the development of physics farther east than most popular scientific histories in English do. He also presents a number of phenomena that readers can try out in their backyards."
– Harry Eagar, Maui News
"Sure we all know it's blue, and most of us know why. Or, at least we think we know why. This book shows that our sky comes in as many shades of blue as a painter has in their palette. But each shade has a natural explanation, hence the size and value of this enlightening book. Hoeppe's book works through humanity's understanding of the phenomenon of the blue sky by advancing chronologically [...] [The] attention to detail, the thoroughness of his review and the vibrant style of writing (even though a translation) make this book worthwhile reading."
– Mark Mortimer, Universe Today
"This wonderful, discursive book begins with a child's common question and proceeds to provide and interdisciplinary answer with historical perspective and insight [...] [Hoeppe] enhances the very perception of both the immediate and farthest reaches of the universe."
– N. Sadanand, Choice
"Why the Sky Is Blue is popular science at its best. In fact, it is considerably more than that: in ten chapters, an epilogue, several appendices, notes, and a bibliography of further reading, the book provides a broad overview since classical antiquity of how scholars have grappled with explanations for the intriguing blue color of the sky above us all. As it turns out, the simple question, why the sky is blue, requires a veritable tour de force through western cultural history and the history of science for a complete and satisfactory answer."
– Hans J. Rindisbacher, European Legacy
"The subject of this book is interesting enough in its own right, but equally importantly, it is an informative case study of the ways that human thinking has progressed in our attempts to understand the world in which we live."
– David Kay, Cosmos Magazine
"Why the Sky Is Blue answers an ancient and surprisingly complex question in an entertaining and accessible way."
– Lunar & Planetary Information Bulletin
"Overall, I found the book to be very well written and translated, well illustrated, and an easy and quite enjoyable read. The author makes use of a number of stories to enhance the subject matter that will make this a very useful textbook for those teaching high school or lower-division undergraduate level courses on the subjects of optics, atmospheric science, and history of science. Noting that there are few books that are currently available on the subject that deal with this historical perspective, I would wholeheartedly recommend this book."
– Jeffrey S. Gaffney, Bulletin of the American Meteorological Society
"This delightful combination of science and history should be required reading for poets, pilots, artists, weather watchers, and anyone who ever marveled at the manifest colors of the sky or wondered why it is only sometimes 'blue.'"
– James Rodger Fleming, Colby College
"An absorbing study of historical approaches to the everyday fact of the blue sky above us, Götz Hoeppe's Why the Sky is Blue is full of revelations. The story it tells of the sky's appearance as an issue of speculation and investigation will appeal both to the specialist and the general reader."
– Eileen Reeves, author of Painting the Heavens: Art and Science in the Age of Galileo
Praise for the original German edition:
"In this richly illustrated volume, the author describes and explains the color and appearance of the firmament, from earlier times to the current day. It is an exciting excursion from mythology, art, and philosophy up through modern science."
– Die Welt
"This is a multilayered book that makes a seemingly commonplace observation the starting point of an exciting journey of discovery [...] The color of the sky proves to be the key to understanding many of our cultural achievements in science, art and everyday life."
– NDR 1's Bücherwelt
"Hoeppe has succeeded in something completely special: the book combines the research of the natural sciences with philosophical and cultural reflections – all elegantly expressed."
– Saarländischer Rundfunk