In a theory of the rainbow that approximates the behavior of light as a series of rays, the Descartes ray is the one that undergoes a minimum angle of deviation as a result of being refracted as it enters the drop, reflected one or more times within the drop, and then refracted again as it leaves. The significance of the Descartes ray (in this model) is that the radiance is markedly greater than that of neighboring rays. The Descartes ray is thus useful for providing an approximate rainbow position and color order.