Customer Reviews

Why the Sky Is Blue: Discovering the Color of Life

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This book could as easily have been titled "Is the Sky Blue?" And the answer to that is yes and no.
Gotz Hoeppe, a German science journalist, points out that the sky near the horizon, if clear, is whitish not blue.
So when a child asks her father, "Daddy, why is the sky blue?" one answer could be: Take a closer look.
A longer, yet still incomplete, answer would be: Light from the sun hits viruses and molecules of gas in the atmosphere and is reflected as blue light. The sky itself -- mostly nitrogen and oxygen -- is colorless.
Figuring this out took a long time. The Greeks about 2,500 years ago were the first to become dissatisfied with mythical answers, but although they put a lot of effort into proposing reasons, they did not know how to test them.
Hoeppe traces the thinking of prescientific physicists through 2,000 years before getting to the period when real answers started to be found.
"Why is the sky blue?" is a childish question but answering it was not child's play. The first clues began to be teased out 400 years ago, and the big breakthrough came with Isaac Newton's experiments showing that white light is composed of colors, including, of course, sky blue. Newton published "Opticks" in 1704.
Some of his ideas were wrong, which began to be recognized about 50 years later. It took another hundred years to straighten most things out, but another 50 after that for Albert Einstein (and others) to explain the weird qualities of light.
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.
For example, the "blue hour." When the sun goes down, the sky stays blue for a while. The hue is almost, but not quite, the same in the blue hour as during bright daylight, but the mechanism for producing it is entirely unrelated.
A careful look at the sky, with Hoeppe's guidance, will reveal a number of other curiosities that we tend to overlook.
Unfortunately, Hoeppe's guidance goes awry in his summation, when he raises the alarm about what increased carbon dioxide is likely to mean for the blue sky.
The answer, very likely, is nothing, thanks to clouds and other buffering effects, but -- astonishingly -- Hoeppe manages to write about greenhouse gases for two chapters without mentioning the most important one -- water vapor.
It wouldn't hurt to skip Chapter 10.

When an author writes a book on a technical matter and aims it at a fairly broad readership, it is very important that he/she ensures that the text is very clear and accessible, authoritative yet friendly, very engaging and limited in specialized jargon. In my view, the author of this book has succeeded beautifully on all counts. Beginning with the philosophical musings of the ancient Greeks, various attempts at explaining the blueness of the daytime sky throughout history (up to the present) are brilliantly presented and discussed in detail. Since this book was originally written in German, well-deserved credit also goes to the translator who has done his share in ensuring that this excellent book retain its essence as a model of clarity into the English language. Amply illustrated with photos, diagrams, tables, graphs and colour plates, this well-referenced book can be enjoyed by anyone. Although readers who do not have a science background may be slowed down a bit by some passages, science buffs will likely find this book particularly satisfying. Overall, I would definitely rank this popular science book among the best of its type that I've read.

If you have any penchant for physics and enjoy the human adventure that goes with it, then you will enjoy this book, perhaps as much as I have. The author takes us back in time, and places us in the minds of those early Greeks who could only speculate as to the cause behind the beautiful blue in the sky. It is remarkable just how far and to what great heights, literally, mankind has tried to tackle this topic. Hoeppe carries the reader along this marvelous adventure, and does so with a cogent style that makes even the more complicated points easy to grasp.

Many other related subjects are addressed throughout the book that are handled in-depth and give us a view we are unlikely to find elsewhere. John W. Strutt's, Lord Rayleigh, original mechanical treatment for scattering is nicely explained, followed by a close look at his modern electromagnetic modification to it once Maxwell revealed light is an electromagnetic wave.

I especially enjoyed learning of the Chappuis Effect - it might explain the purple color of our Moon during a lunar eclipse when volcanic activity has altered our atmosphere.

With over 250 exoplanets discovered, and thousands more to come, this book will help us understand what we may someday behold when we actually obtain visible images of them. It already helps us understand what we see for the atmospheres of our neighboring planets. For instance, why the Martian sky is not blue and why the cloudless regions on Saturn are a rich sky blue color.