14 Nebraskaland • March 2022
IN THE FIELD
After a weather front has passed, often an
overcast and rainy sky magically transforms into
a crisp indigo-blue with the air so clean you can
almost taste the freshness. This shade of blue
seems to resemble cobalt tropical ocean waters
and can occur without so much as a single cloud
to dot the hemisphere.
What you are witnessing, quite purely in this
case, is Rayleigh scattering, named after an 18th
century British physicist who discovered the
physics of why the sky is blue. Visible light in
the wavelengths emitted from the sun appear
as white light, but is actually composed of all
colors of the rainbow (see "Seeing Double" in
the Aug/Sept 2021 issue). Blue is on the shorter
wavelength end of the visible spectrum, while
red is longer.
In the clearest of air and after a front passes, the
indigo and blue can appear quite vividly. Because
the size of gas molecules and tiny particles in
the atmosphere is similar to that of blue light
(0.00002 inch), this wavelength is very effective
at scattering these hues. For the human eye,
scattering means we see it, sometimes brilliantly.
Contrast this with a warm and humid summer day.
While typically not visible to the naked eye,
microscopic particles such as water vapor,
dust and pollen can be quite prevalent in the
atmosphere. These larger particles result in Mie
scattering, named for a German physicist, which
spreads all wavelengths of solar energy. The
result is often a paler shade of blue, which can
fill either the whole sky or most often just near
the horizon.
But not to worry, the pale shade is not you, it's
Mie.
IT'S NOT YOU, IT'S MIE
By Martha Shulski
Sandhill cranes fly in a cloudless sky the morning after a rainstorm in Hall County. JEFF KURRUS, NEBRASKALAND
