The Bamberg herald. [volume] (Bamberg, S.C.) 1891-1972, 1916-02-10

s5ISWe snail not KNOW eAdclly WAdI
the conditions are around the north
pole until people go and live there.
Theoretically there are about. six
months of continuous night at the
Y pole, beginning when the sun sinks
below the equator at the autumnal
equinox September %, and ending
when it rises above the equator again
at the vernal equinox, March Il. At
ter September % the region of polar
night begins to extend jsouthward
until, at the time of the winter sol
stice, December 21. it attains the
Arctic polar circle, about % IL de-
grees south of the pole, and in lati-
tude about sc IL degrees north of
the equator. Along that circle there
Is, at That time, just one sunless day,
or o1e period of "a hours, during
which the sun does not rise
Between the Arctic circle and the
pole the greatest length Of the win.
ter night varies from "a hours up
/ to six months. South of that circle
there are no sunless days. In the
latitude of Great Slave Lake, from
562 to 63 degrees north, the longest
night is about 20 hours. During four
hours of each "a the sun is above
s. the horizon there, even at the Win
ter solstice. =
The theoretical six months night
prevails only exactly at the pole.
About degrees south of the pole
s the night lasts five months; at II 1-3
degrees from the pole, four months;
Hat II degrees, three months; at
20 IA degrees, two months, and at
B ~ 2-3 degrees, one month.
These are the geometrical facts
with which it is necessary to begin.
They would be the actual facts if the
earth were perfect sphere, if it
were not surrounded by an atmos
aphere and if the sun were a mere
point of light instead of disk half
"a degree in diameter. We may ne
glect the effects of the slight fatten-
ing of the earth's poles, and of the
sensible diameter of the sun, but we
cannot neglect those due to the re-
\ traction and reflection of light by the
atmosphere.
BY refraction the atmosphere vir-
tually lifts the sun, when it is. on the
horizon, something more than half a
degree above it's true place. This
alone must shorten the polar night by
four or five days and perhaps week
Sor more, since there is reason to be-
s>lieve that the refraction is greater in
the polar regions than farther south.
But far more effective is the refiec-
s tion of sunlight from the upper air,
4 which is the principal cause of twi-
light.
On the average, evening twilight
lasts until the sun has descended 8
& degrees below the western horizon,
and morning twilight begins when
the sun has risen to within Is de-
grees of the eastern horizon.
Now, as seen from the pole, the
sun goes spirally round and round
the sky, gradually rising from March
s21 to June %, and gradually de-
scending June 22 to September %,
when it again touches the horizon,
and slowly sinks beneath it, day
or two elapsing after the lower edge
reaches the horizon before it's upper
edge sinks from sight.
Similarly, ON the approach of the
vernal equinox, March 21, there will
be morning twilight Of above two
months duration before the sun ac-
tually rises. Thus four months of
the polar night consist of twilight,
and only two months are entirely de-
prived of sunlight.
It is quite possible that on account