Monday, November 20, 2006

Light and Color in the Open Air

"Light and Color in the Open Air" by M. Minnaert is one of the best books ever, one of the few great classics, destined to be carried into innumerable bomb shelters and deserted desert island hermitages.

To the left is an image of the shadow and penumbra of Mt. Wrightson, 9500', at sunset. To the right is the diffraction pattern of a street light through a tree. Minnaaert explains:

"One sees at night, when a street-lamp is shining just behind a tree, that the light is reflected here and there by the twigs; these shining patches are, in reality, shorter or longer lines of light, and all these lines lie in concentric circles round the light-source. Owing to perspective we see branches that lie parallel to the plane of incidence greatly shortened, whereas those at right angles show their full length. Since there are as many branches to be found in either direction, we shall see light lines mainly at right angles to the plane of incidence. Each shining ring can be traced to a definite branch or twig. " [paraphrase]

This has some similarity to x-ray diffraction.

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