The Anderson intelligencer. [volume] (Anderson Court House, S.C.) 1860-1914, 1899-05-17
TWILIGHT'S LENGTH.
HOW IT VARIES AT DIFFERENT TIMES
AND PLACES.

when 1t In at Hts Shortest All Over
the Globe, 1t Lasts For Thirty aian-
Days at the Poles.
The belief that there is little or no
twilight within the great tropical belt
encircling our planet is very wide
spread one. History. however. warns
US that beliefs need not necessarily ac.
cord with facts. 1t might indeed almost
be eaid that they usually do not
The roiling and moiling millions. the
humble units that, taken in the bulk,
constitute what Is called 'great pow
er, have neither the time nor the in
clinatiOn to overhaul their opinions.
They are not assailed by doubts as to
whether the intellectual coffee which
they have at odd moments imbibed
may not have been mostly chicory
Such state of mind unquestionably
makes more happiness. and although
such happiness may bear rather too
much resemblance to that Of. say, the
cow it is none the less real for all that.
Twilight is at it's shortest at the
equator and increases with the latitude
at the equinoxes-at about the same
rate as that at which the meriCians de-
crease their distance from one another
The increase is. therefore. very slow in
low latitudes and very rapid near the
poles.
Practical or civil twilight is the time
which elapses between the moment Of
+, uY7v, IN
he is seven degrees Of n great circle be-
low the horizon. At the equator this
time cannot. Of course. be less than 90
minutes. At the edges of the tropic
zone it is about 81 minutes
A person with good eyesight will.
should he care to make the experiment.
find that when at sea and on or near
the equator he is able to read average
type on deck for at least % minutes
after the sun has set without tho aid of
artificial light and when there is no
moonlight.
This is the common sense experiment
Of which the duration is considerably
longer than the practical. and even at
the equator something like 20 minutes
will elapse before night holds undis-
puted sway. This is the length Of the
true, the astronomical twilight.
1t is at or near the equinoxes that the
phenomenon under consideration is at
its shortest all over the globe. At those
periods it lasts at Honolulu 80 minutes !;
at San Francisco, 35; at London. 45; ;
at st. Petersburg, 81 at the Arctic and
Antarctic circles. 70, and at the poles.
1S days. When, then, we say that the
poles have six months light and six
months darkness. it is little mere than
facon de parler.
The north pole has no less than 22a
days OF practical daylight each year. the
south pole 215 days, and the equator
1877 days. Nansen, when in high NORTH
ern latitudes. was able to read The
Verdensgang many days before the
longed for sunrise following the long
winter night. The great length of the
twilight in polar regions is boon in
deed to explorers. The popular imagina-
tion usually attaches itself to the great
cold they have to endure. but the real
enemy is the long darkness. which ia
trying to the enthusiasm Of even
Nansen, Peary or a jackson.
the length OF the twilight at TIE eaua-
tor at the equinoxes and solstices. Even
at Honolulu it will not vary By more
than couple Of minutes But in the
higher latitudes the varying duration
is very marked. In latitude 5811 de-
grees. for instance, it lasts 90 minutes
at the equinoxes, but in the summer
Eolstice it lasts from sunset till SUNRISE
that is to say, from 9:10 o'clock till
3 $50. or five hours and 40 minutes
North or south Of 83 degreespractica
twilight lasts all "night'' at the eqni-
nOxe. The sun is, it iB true, only 12'
hours above the horizon, but as he eau
not yo more than z degrees below it
there Is continual daylight for the a.
hours. In such cities as Stockholm and.
st. Petersburg there are close OH. to IA
hours of daylight at those seasons when
day and night are said to. be equal, and
at the equator itself the day all the
year round is made Vi 8 hours daylight
and II hours darkness It must not be
forgotten that in those ATTITUDES where
the sun remains for months below the
horizon there is during that period
good deal Of daylight, 30 that along the
eightieth parallel north "a little north
Of which the Jackson n-Harmsworth ex-
petition spent three consecutive years
in the Franz Josef islands). although
the sun does not rise between Oct. 10
and Feb. %. there is period. Of three
weeks following the final. sunset and
another Of the same length preceding
the first sunrise Of the year. on each
day Of which good type can be read for
a few minutes up to some hours with
out artificial light. FRANCISCO Call.
Some Curious Clubs.
New York has new feature in clubs.