Bending again on the way out

Light leaving the drop

The reflected light travels to the lower front of the drop and passes back into the air. It bends once more on the way out, and the colors spread even further. Yellow light leaves about 42° below the direction of the Sun. Red leaves at about 42.4° and violet at about 40.6°, so each color has its own exit angle.

Why?Light bends twice, once going into the water and once coming out, and both times violet bends more. So the light from a single drop fans out, each color in a slightly different direction.

Learn moreRed and violet leave about 1.8° apart. A rainbow’s band in the sky is about that wide too, roughly the width of one or two fingers held at arm’s length. On the protractor, 0° points toward the Sun (the incoming light turned around).

Exit angle (yellow light)

42°

Red leaves at

42.4°

Violet leaves at

40.6°

calculated from the refractive index of water (IAPWS, 20 °C) and the laws of refraction and reflection