An international team of scientists working with Disney have figured out how twin rainbows form while trying to enhance rainbow images in computer graphics.
Rendering results for different types of rainbows: (a) Rainbow derived from Lorenz-Mie theory; (b) Single primary rainbow with considering the angular view of the sun; (c) Double rainbow with a flipped secondary rainbow; (d) Multiple supernumerary rainbows caused by small water drops with uniform sizes; (e) Twinned rainbow resulted from mixture of non-spherical water drops and spherical ones. (Iman Sadeghi, Adolfo Muñoz, Philip Laven, Wojciech Jarosz, Francisco Seron, Diego Gutierrez, Henrik Wann Jensen)