Evening star., 1951-10-17
Blue Aurora Boreulis
Seen in Arctic Down
Rare Occurrence Reported
By Navel Test Stution
By Thomos R. Henry

By Thomos R. Henry
A blue aurora borealis, hitherto unob-
served phenomenon Of the Arctic dawn,
has been reported here.
It is believed to be at least as rare an
occurrence as "blue moon" and much
more striking.
The strange event IS described by Drs.
D. Barber and D. r. Williams Of the
q. s. Naval Ordnance Test Station at
1nyokern. Calf. who saw it while carry
ing out studies of the physics Of the
upper atmosphere near the University Of
Alaska.
Ordinarily, the northern lights, most
striking display OF the Arctic heavens,
range from shimmering white through
pale green's and reds. Their cause still
Is not entirely understood. It now is
generally believed, however. that they
are due to streams of minute particles
spurted from the surface Of the sun,
moving through empty space with a
speed approaching that of light, and
being pulled toward the polar regions
by the attraction Of the magnetic pole
area.
There the particles break up or
"ionize" atoms in the extremely tenuous
atmosphere 200 miles or more above
the earth. AS the atoms lose outer elec-
irons, the energy released appears in
the form Of light which takes the shape
Of long, Pickering arches across the sky.
Disappears at Sunrise.
The phenomenon disappears generally
at sunrise because the suns light browns
it out. These aurora displays are closely
associated with magnetic storms and
radio disturbances on earth and afford
one Of the few means by which informa-
ton can be obtained on conditions in
the atmosphere at extreme attitudes.
The blue aurora described BY Drs.
Barber and Williams came at dawn in
late February, according to their report.
recently published in the Journal Of Geo.
physical Research of the Carnegie 1nsti-
tuition Of Washington.
just before dawn they observed q
broad auroral arc of conventional type
extending completely through the zenith
of the Arctic sky. The change occurred
"instantaneously." Filaments of the
aurora increased in brightness 10 to 20
fold and became an unearthly blue in
color. The phenomenon continued for
about 10 minutes. Then it vanished
nearly as suddenly as it had appeared.
The filaments are described as looking
like gigantic squirming blue snakes in
the heavens.
Drs. Barber and williams tentatively
attribute the phenomenon to combina-
ton of events in the high atmosphere
which probably has existed rarely since
the beginning of time. Far to the east
ward dawn was breaking. Although not
apparent at the Alaska station, solar
radiation had struck the extremely high
altitude at which the aurora existed.
The effect Of this ordinarily would be
to cause the aurora to fade away.
Effect of Combination.
But simultaneously, Drs. Barber and
Williams believe, there must have been a
great increase in auroral activity-per-
haps an exceptional large stream Of the
infinitesimal particles. The effect Of
the combination was to produce the blue
aurora. E-..z.
AS the 'blue snakes" faded away, q
brilliant band of green flashed through
the zenith. Later, toward the south,
there appeared patch of white light
like strato-cirrus cloud which persisted
for few minutes before melting away
in sky which by that time had become
too bright with the normal light of
dawn to permit it to be observed.
The colors of the aurora are due to
the wave-lengths of light emitted by the
atoms ionized by the particle streams or
possibly by ultraviolet light, accord
ing to other theories. Each element
emits light of different wave-lengths,
and hence different colors. BY isolating
these wave-lengths with a spectrograph
it is possible to determine what ele-
ments, such as nitrogen and oxygen, are
present at extreme attitudes.
The Spectrogram of the blue aurora,
however, did not reveal anything un-
usual, probably due to the very brief
interval during which it could be OBJ
served.
Throughout much of the preceding
night, Drs. Barber and Williams re-
port. the aurora had been very active,
with ill-defined brick-red patches inter-
spersed through diffuse veil of green
which extended over large part of the
sky. The patches apparently were unre-
lated to the veil.
Drs. Barber and Williams made ex-
tensive spectroscopic observations both
OF the aurora and the normal faint lu-
mineScence of the night sky. They
found about Is light lines which could
not be identified because Of their ex-
treme weakness but which probably be-
long to elements known to be present
in the high atmosphere.