The Blue Hour
During twilight I’ve noticed a curious dark blue cast to the sky, apparently more visible to my camera than to my naked eye.
More prominent late in dusk, early in dawn, when the sun is significantly below the horizon, does anyone else notice this?
Is it produced solely by the camera?
What causes it?
Refraction, in a word.
As Isaac Newton demonstrated thru the use of a prism in the mid 1600’s, visible light consists of a spectrum ranging from red to blue, the long wavelengths of red to the short wavelengths of blue. The atmosphere, that thin skin allowing life, about 300 miles thick, the most important part about 10 miles thick (compared to the radius of the earth, roughly 4,000 miles), bends light, refracts it, scatters it, the short wavelengths more than the long, the blue more than the red.
Thus, blue light bounces around the region of the atmosphere closest to us, whereas red light spills out and is less visible. In the same way that leaves turn color—not by addition, but by subtraction, the green of chlorophyll disappears in autumn with the end of chlorophyll production, rendering the already present bright colors to shine.
Physics does not explain why the Blue Hour appears more vividly thru photographs than to the eye. Is it simply that we are less aware than our camera, less attentive, fooled by habit? As Thoreau wisely put it, Only that day dawns to which we are awake.
The Social Landscape on Tumblr