An instructive problem in the geometrical optics of caustics is afforded by the classical theory of the rainbow. Since any caustic may also be viewed as a cusp locus of wavefronts, the same problem has bearing on certain aspects of the diffraction theory of the rainbow. Using a method of caustic analysis capable of delineating the complete emergent caustic of the primary rainbow, it is shown that past conceptions of the full caustic locus have been markedly in error. The correct locus is found to exhibit an odd cusp on a segment of the (virtual) caustic lying wholly within the raindrop.

Topics
Atmospheric optical phenomena, Diffraction theory, Geometrical optics, Optical aberrations
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© 1963 American Association of Physics Teachers.
1963
American Association of Physics Teachers
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