The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1894-06-21
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minutes above the south point of the hor-
lion, or twice the obliquity of the ecliptic.
But what is the suns position at
midnight at the Arctic circle
South of this point the sun dips
below the horizon. increasing his mid
night depression as we go south. But on
the Arctic circle he is seen just TO touch
the north point OF the horizon at midnight
He sets AMI rises at the same time, and the
day is twensy-four hours long. So in pass
ing from the Antarctic to the Arctic circle
on June q we. have passed through all
variations of the length of day from zero
TO twenty-four hours. At the winter
solstice, on December n. the same features
will appear in travelling from the Arctic to
the Antarctic circle.
North of the Arctic circle there will of
course be perpetual day, the suns meridian
altitude at noon always being greater than
his elevation at night until the north pole
is reached. where the sun appears to move
in circle parallel to the horizon. Here
the perpetual day limit runs from March
20 to September - Between these
dates, if the suns diurnal course in the
armament could be marked, 1t would APP
pear TO be not IN exact circle, but a beau
tiful spiral. having its base in the horizon
and rising % degrees q minutes above the
horizon.
Again taking our place at the Arctic
circle, let US move south. have said the
sun will dip below the horizon at mid
night, this depression increasing as we go
south. This means that the length of the
nights will increase. The twilight will,
however, last all night until we reach lati-
tude As degrees SO minutes. Below this
parallel there will DE some period of abso-
lutte darkness. For instance. on the par
aliel of AZ degrees the evening twilight viii
last till about Ii o'clock. The morning
twilight will begin at l O'Clock, giving
abou, two hours of total darkness.
Another interesting feature of the long
est day is 10 note the length of shadows
cast at noon as compared with their length
on the shortest DAY. 1t is easy TO see that
the higher the altitude of the sun the
shorter the shadow. Accordingly the
shadow cast by an object on June 81 Is
much shorter than the shadow cast by the
same object on December n How much
is this difference? This, of course, de-
ponds on the latitude of the place. In
order that the reader may make a COM
parison | will give the number by which
the length of an object must be multiplied
in order to give the length of the shadow
cast at uoon on June 81 and December 81
for the following ATTITUDES:
Latitude June sf. Dec Ell.
20 deg. n min. (Tropic Cancer). 10000 1.u6e62
81 deg. 4 min. (San Francisco .2a5s26 .S2276
II deg (0lympia) ....-.........-- .4S5s = $500
&c deg. s3 min. (Arctic Circge),. .9357SS Infnity
Now let US compare the amount of heat
received from the sun on June 81 and De-
cember 81.
Since this depends upon the direction
with which the suns rays strike a given
place on the earth, the suns altitude will
regulate this supply of heat, and this in
turn will depend on the latitude of the
place.
Taking the same parallels given above.
we have the following figures expressing
the relative amount of heat received June
n and December 81 considering the heat
received when the sun is in the zenith as
unity: