16 Nebraskaland • August-September 2021
IN THE FIELD
Roy G. Biv — my make-believe weather friend
that helps me recall the colors of a rainbow. Red,
orange, yellow, green, blue, indigo and violet are
the colors in this spectrum and also their order of
appearance.
Rainbows represent optical phenomena that
are a function of time and place. They also require
just the right combination of atmospheric water
droplets, sunlight and viewer perspective. Often
they are a nice conclusion to a passing rain shower.
Similar to a prism, water droplets suspended
in the air both reflect and refract sunlight,
separating the wavelengths enough so we can
see white light's colorful display. The angle of
reflection when visible light goes through water
droplets is 42 degrees.
Red is the longest wavelength in the visible
spectrum and bends the least; violet is shortest
and bends the most. Position is everything with
these charming optics, as the water droplets must
be in front of you with the sun's illumination to
your back.
Sometimes you are fortunate to see a secondary
rainbow positioned above the primary, and
typically brighter, rainbow below. This second
bow is simply due to one more bounce of sunlight
in the water droplets. The extra reflection causes
the light spectrum to exit drops at a 50 degree
angle. It also results in a reversal of colors with
red on the bottom and violet on top.
Next time you are treated to a bright rainbow,
look slightly skyward to perhaps see double.
Martha D. Shulski, at the University of Nebraska-
Lincoln, is the director of the Nebraska State
Climate Office.
A double rainbow decorates the sky above the Republican River west of Indianola. JUSTIN HAAG, NEBRASKALAND
SEEING DOUBLE
By Martha Shulski
