Swiss alpinist Horace-Bénédict de Saussure (1740-1799) wondered how the blue of the sky changes with altitude.
He observed that the color of sky was lighter close to the horizon. He suspected that the blue would get darker at higher altitudes, but how much darker? Legend had it that if you climbed to the tops of the Alpine peaks, the sky would be black, and there was a risk of “falling into the void.”
So he made a “cyanometer,” by dipping swatches of paper into a suspension of Prussian blue in order to obtain nearly sixty evenly spaced swatches of blue ranging from white to black.
In 1787, Saussure hired two guides and undertook a three-day trek to the 15,780-foot summit of Mont Blanc. When he tested his cyanometer against the sky, it matched swatch 39, the darkest he had ever seen.
Although our modern understanding of scattering of light by air molecules still hadn’t been completely figured out, Saussure had made an important breakthrough. On top of a very tall mountain, there is less air above the observer to scatter the sunlight and produce a blue veil over the blackness of space.
When I painted the temple on the highest peak of Dinotopia, I made sure to use a darker blue for the sky, and a more abrupt transition above the horizon.
Full story of Saussure's Cyanometer at the RCS Chemical Sciences website
Wikipedia on Saussure
Wikipedia on Mont Blanc
Previously: How to make your own cyanometer from blue paint chips from the hardware store
Reproduction of Palace in the Clouds in Imaginative Realism
More about "sky blue" in Color and Light
Palace in the Clouds from Dinotopia: A Land Apart from Time - The 20th Anniversary Edition