Question 08/99

ZEROTH ORDER RAINBOW

A ray of light coming from the sun (A) enters a water drop, is reflected internally once, and exits in direction B. The angle of maximal intensity of this reflected light depends on the index of refraction of the water and thus is slightly different for different colors. This gives rise to the primary rainbow at about 42 degrees opposite to the direction of sun. (The secondary rainbow corresponds to two internal reflections.) Question: Why can't we see a zeroth order rainbow by looking at rays like C that exit the drop without internal reflections?

This problem was suggested by D. J. Bergman

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