" Blue Sun "

" Blue Sun " September 1950

One of the best-documented occurrences
this century,happened during September 1950.

"The skies took on strange colors"

Strange sorts of lights,
followed by almost complete darkness.
Varying shades from pink and orange
to yellow and brown filled the sky .

The sun disc appearing and disappearing
through breaks in the clouds,
appeared blue or purple,

This incident was reported
in the scientific journal, Weather.


Like blue skies
blue, green or lavender
suns and moons,
owe their color to
scattering of light
in the atmosphere.

The difference is in the size
of the particles doing the scattering.

The sky is blue because the molecules of air
are much smaller than the wavelength of visible light.

Blue light has a shorter
wavelength than red,
and reacts more strongly
with the tiny molecules
than red does.

The blue light is thus scattered more than red,
and we see the scattered light of the sky
as blue and the sun as reddish,
especially when it is low in the sky
and must pass through a lot of air to reach our eyes.

The effect is called Rayleigh scattering,
and it is responsible for what is called Tyndall blue.

Blue eyes, some blue feathers,
and the bluish color of the veins in your skin
are all due to Rayleigh scattering.

Particles that are much larger
than the wavelength
of light scatter all wavelengths
about equally.

Clouds and snow
are made up of particles
several times larger than
the wavelength of light
and they look white.

Blue suns and moons
and pinkish skies
occur when there are particles
in the air whose size
is just a little larger
than the wavelength of light.

These particles can resonate with light
so that certain wavelengths are strongly scattered,
while others are only affected
about half as strongly.

Oily droplets about 1 micrometer across
(a twenty-five thousandth of an inch)
will scatter red light strongly,
while letting blue light pass through,
just the opposite of Rayleigh scattering.

On September 23, 1950,
several muskeg fires
that had been quietly smoldering
for several years in Alberta
suddenly blew up into major
and very smokey fires.

The winds
carried the smoke
eastward and southward
with unusual speed.

The conditions of the fire
produced large quantities
of oily droplets of just
the right size to scatter red
and yellow light.

Wherever the smoke cleared enough
so that the sun was visible,
appeared lavender or blue.

Ontario and much
of the east coast of the U.S.
were affected by the following day.


Two days later...
observers in England
reported an indigo sun
in smoke-dimmed skies,
followed by an equally
blue moon that evening.

Forest fires
are not the only possible
producers of blue suns.

Fine, far-travelled dust
and also volcanic ash
has been known to produce
the same effect.


Many of the scientific articles written
about the blue sun of September 1950
mentioned also the strange optical effects
produced by the eruption of the volcanic
Island of Krakatoa a century ago.

The important point
is the particles
in the atmosphere
must all be very close
to the same size,
and that size must be about
a micrometer across,
a combination of circumstances
that occurs literally
once in a
"BLUE MOON".