Vilas County news. [volume] (Eagle River, Vilas County, Wis.) 1896-1927, 1899-05-15
TWILIGHT IN THE TROPICS.
How Long it Really Lasts After the
Sun Has Set.

How Long it Really Lasts After the
Sun Has Set.
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 &C
cord with facts. 1t might indeed al
most be said that they usually do not.
The toiling and moiling millions, the
humble units that, taken in the bulk,
constitute what is called great
power" have neither the time nor the
inclination to overhaul their opinions.
i ney are not assailed by doubts as to
whether the intellectual coffee which
they have at odd moments imbibeo
may not have been mostly chicory.
Such a state of mind professionally
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.
L
equator and increases with the lati-
tude-at the equinoxes-at about the
same rate as that at which the merid-
ians decrease their distance from one
another. The increase is, therefore,
very slow in low ATTITUDES and very
rapid near the poles.
Practical, or civil, twinghr Is the
time which elapses between the mo-
ment of the suns setting and the mo-
ment when he is seven degrees of a
great circle below the horizon. AT
the equator this time cannot, of course,
be less than twenty-eight minutes. At
the edges of the tropic zone it is about
thirty-one 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 twenty-eight minutes after
the sun has set without the aid of arti-
fetal light and when there is no moon
light. This is the common sense ex'
pertinent by which the duration ofprac-
teal twilight has been determined.
The actual duration is considerably
longer than practical, and, even at the
equator, something like seventy min
utes will elapse before night holds I'M
disputed sway This is the length Of
the true-the ronOmical-twilight
It is at or near the equinoxes that
the phenomenon under consideration
is at it's shortest all over the globe.
AT those periods it lasts at Honolulu
thirty minutes; at San Francisco, thir-
ty-five; at London, fOrty-fve; at st.
Petersburg, fifty-seven; at the arctic
and antarctic circles, seventy-two, and
at the poles, eighteen days. When,
then, we say that the poles have six
months light and six months dark
ness, it is little more than facon de
parler. The north pole has no less
than 222 days of practical daylight
each year, the south pole 215 days, the
equator 1877 days. hansen, when in
high northern ATTITUDES, was able to
read the ''Verdensgang' many days be-
fore the longed-for sunrise following
the long winter night. The great
length of the twilight in polar regions
is a boon indeed to explorers. The
popular imagination usually attaches
itself to the great cold they have to
endure, but the real enemy is the long
darkness, which is trying to the enthu-
siasm of even a Nansen, a Peary or a
Jackson.
There is practically no difference in
the length Of the twilight at the eQua-
tor at the equinoxes and solstices.
Even at Honolulu it will not vary by
more than a couple of minutes. But
in the higher latitudes the varying du-
ration is very marked. In latitude
591h degrees, for instance, it lasts fifty
six minutes, at the equinoxes, but at
the summer solstice it lasts from sun
set to .sunrise-that is to say, from
$40 o'clock~till $50, or for five hours
and forty minutes.
North or south of SO degrees prac-
| teal twilight~lasts all might at the
! equinoxes. j The sun, is, it is true, only
twelve hours above the horizon, but
as he cannot get more than seven de-
grees below it, there is continual day
| light for the twenty-four hours. In
such cities as Stockholm and St. Pc
! tersburg there are close on to four.