Why the Sky Is Blue, by Götz Hoeppe is subtitled “Discovering the Color of Life,” so I was a little puzzled when Princeton University Press asked me if I wanted a review copy. But, hey, free books!
This is ultimately a physics book, but it’s really in the category that I think of as “Smart People Books,” those books that take an exhaustive look at some phenomenon from a wide range of different perspectives. In this case, it’s a survey of several thousand years of thought about the blue color of the sky.
This is an extremely comprehensive look, and I’d be surprised if there’s any historical thinker who wrote about the color of the sky who wasn’t included. Hoeppe starts with ancient Greek philosophers, who thought that blue was a mixture of black and white, and works his way forward through Arabic commentaries on Aristotle, medieval treatises on painting, Newton’s experiments with prisms, Goethe’s color theory and on up through the nineteenth-century development of the theory of Rayleigh and Mie scattering, that eventually provide the correct physical explanation for the blue color of the sky. Along the way, he provides plenty of illuminating historical anecdotes, and points out numerous interesting phenomena regarding the sky and its color. Some of the material presented is stuff I already knew, other bits were new to me (I didn’t know about the role of ozone in the color of twilight, for example).
The subtitle comes out of an argument made in the final chapter, that the blue color of the sky is in fact due to the presence of life on Earth. The relatively large fraction of oxygen in the Earth’s atmosphere is thanks to the action of photosynthetic algae and other plants, and without that, the color of the sky would be very different. It’s an interesting claim, though it seems to mostly serve as a means to tack on an environmental message, which I could’ve done without.
The earlier chapters on philosophical and artistic approaches to the color of the sky are very accessible to readers with little knowledge of the subject. The later, more physics-oriented chapters might prove rough going for a non-scientific reader, though. Equations are mostly confined to the appendices (which include a really nice explanation of how to get the wavelength dependence of Rayleigh scattering from dimensional arguments), but there are some fairly detailed discussions of the physical processes involved in light scatering by turbid media and polarizable particles, which get a bit thick in places.
The book contains numerous figures, raging from graphs of important scientific results to photographs of the various people involved in the story, to reproductions of famous works of art. Some of the more techncial figures could be explained more clearly, but in general, the selection of illustrations is good, and they cover most of the important phenomena.
This was originally published in 1999 in German, and is credited as “translated with John Stewart.” I suspect that this means John Stewart assisted the author in translating his own work, and not that the work was translated by peering through John Stewart like some latter-day Joseph Smith working on the Book of Mormon, but I don’t know the terms of art for this area. However the translation was done, the English version is very clear and free of the awkward constructions that sometimes mar translated works.
On the whole, this was a very entertaining look at a subject that I wouldn’t have thought had quite this much depth. Hoeppe manages to intelligently discuss a remarkable range of human activities using the color of the sky as an entry point, and it’s a good read from start to finish. If you enjoy the category of Smart People Books, this is worth a look.