Democratic messenger. [volume] (Snow Hill, Md.) 1869-1973, 1899-05-27
TWiLIGHT'S LENGTH.
HOW 1T VARIES AT DIFFERENT TIMES
AND PLACES.

/ eNiNG 7 @FNSG0s
When u Is Rt Its shortest All Over
| the Globe. u LASTS For Thirty Min
| utcs ut Iinno:uim aud For Eighteen
Days at the Poles.
The belief that there is little or no
twilight within the great tropical belt
encircling our planet is a very wide
spread one History, however. warns
us that beliefs need not necessarily az
cord with facts. 1t might indeed almost
he said that they usually do not.
Tho toilng and moiling millions. the
humble units that, taken in the bulk.
constitute what is called great pow
er. E" have neither the time nor the in
clination to overhaul their opinions
They are not assailed 10y doubts as TO
whether the intellectual ccfTec which
they have at odd moments imbibed
may not have been mostly Chicorv.
Such IA state of mind unquestionably
makes more happiness. and although
such happiness may bear rather too
much resemblance To that of. say. the
Twilight is ut its shortest mt the
equator and increases with the latitude
at the equinuXcS ut about the same
rate as that at which the meridians de-
crease their distance from one another.
The increase is. therefore. very slow in
low ATTITUDES and very rapid near the
poles.
Practical civil f,x.tli.rl,f i fl,.,
which elapscs between the moment Of
the sun ) setting and the moment when
he is seven degrees of great circle be-
low the horizon. At the equator this
time cannot, of course. be less than %
minutes. At the edges of the tropic
zone il is about 81 minutes
a person with good cycsight will.
should he care 10 make the experiment.
find that when at STA and on or near
the equator he is able tn road average
type on deck for at least 2S minutes
after the sun has set without the aid of
artificial light and when there is no
moonlight.
This Is the common sense experiment
of which the duration is considerably
ifAfr-'i aiisaAi AhE tiA"i fN'h dt
the equator something like 20 minutes
will elapse before night holds undis-
rutcd sway This is the length Of the
true. the Astronomical twilight
Ii is nj or near the ,quinoxes that the
phenomenon under consideration is ut
its shortest all over the globe. At those
periods it lasts ut Honolulu 80 minutes;
4 Sun fsrut,..sA,, .,t I,nI,t, 4
nj 81. Petersburg - at the Arctic and
Antarctic circles. -. AMI at the poles,
Is days. Whom. then. we say that the
poles have six months light and six
months darkness. il is little mere than
a facon de- parler.
The north pole has no less than 232
days of practical daylight each year. the
south pole 3i5 days, and the equator
i97 DAYS. Nansen. when in high north
ern ATTITUDES. was able to read The
Nerdrnsgang many days before the
longrd 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
COLI they have to endure, but the real
enemy is the long darkness. which is
trying to the enthusiasm of even
Nansen. Peary or a jackson.
There is practically no difference in
the length of the twilight ut the equa-
tor AT the cquinnNes and solstices. Even
at Honolulu il will not vary by more
than couple of minutes. But in the
higher ATTITUDES the varying duration
is very marked In latitude 59i de
grces. for instance. il lasts ID minutes
at the equinoxcs. but in the summer
solstice il lasts from sunset till sunrise
that is to say. from $40 o'clock till
90. or five hours and 10 minutes
North or south of So degrees practical
twilight lasts all might at the equi
noxe. The sun is. il is true. only IL
hours above the horizon. but as he can
not 20 more than degrees below it
there is continual daylight for the "a
hours. In such cities as Stockholm and
ST Petersburg there are close on to II
hours of daylight AT those Seasons when
day and night are said To hc equal. and
at the equator itself the day all the
year round is made of 3 hours daylight
and hours darkness Ii must not be
forgotten that in those ATTITUDES where
the sun remains for months below the
horizon there is during that period "a
good deal of daylight 81 that along the
eishtieth parallel north "a little north
of which the Jackson n-IIarmsworth ex
petition spent three consecutive years
in the Franz Josef islandsl. 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
IA few minutes mp to some hours with
out artificial light san Francisco Call.