The Princeton union. [volume] (Princeton, Minn.) 1876-1976, 1890-09-25
WHY THE's SKY is BLUE.
Various Prominent Heavenly Tlnts Ana.
lyzed-Why Stars Twinkle.

4 r. i
you have all noticed'a said the pro-
fessor, according to the Cincinnati
Times Star, that when we look away
from the sun into the cloudless sky the
heavens appear blue; when, however,
we look in the direction of the sun,
especially when. after sunset, we look
toward the western horizon the color
is u yellowish red. With the spectro-
scope it can be shown that the white
light from the sun is produced by a
mingling of different colored rays. In.
deed, this can be shown by means of
any triangular prism, say one of the
pendants of chandelier. One Of
these placed in the path of beam of
light will project on Il screen band
of seven colors-red, orange, yellow,
green, light blue. dark blue. and violet.
Understanding this we can readily see
how tie effect is blue when a piece of
blue glass is interposed or red when
red glass is used. All but the blue and
red rays respectively are absorbed;
these, however, pass through freely,
+ and we say that the body is blue or
red, when really the color is not
property of the glass in any true sense
but of the sunli CHIT. What has this to
do with the sky colors? l will now
show you. Dissolve a little white
CASTLE soap in 4 tumbler of water, SO as
to make the water slightly turbid.
Place a black screen behind the
tumbler and hold the whole so that the
sunlight must be reflected from the
liquid before it can reach Your eye.
The liquid will appear blue. Hold it
next in a direct lShe toward the sun and,
it appears yellowish red. Now. these
are the exact appearances of the sky.
Sky light is refracted light. The water
particles IN the atmosphere, like the
particles of soap in the water, refract
blue light; while the background of
darkness surrounding the earth re-
places the black screen. The atmos-
phere, like the solution of soap and
water. transmits yellow and red rays,
but slightly refracted, while the blue,
being weak color, is refracted too
low to be seen; hence when we look
toward the source of light in the even
ing or morning the sky is of yellowish
red color. This effect is more pro-
nounced then than during the Gay, be-
cause when the sun is near the horizon
the rays travel greater distance in
the air in order to reach the earth than
when directly above us. Consequent
ly the blue rays are more thoroughly
refracteu
The atmosphere has many effects in
modifying the appearance Of the sky
and the heavenly bodies. Look at
Venus over there near the western
horizon and just below the crescent
moon. which has come into plain view
while we have been talking Con account
of the deepening darkness). Its real
distance from the horizon is not as
great us it appears. for the rays of
light which it reflects to us and which
it receives from the sun are bent down
ward when they pass into our air.
perhaps fifty miles from the earth's
surface.
LAS the effectois the same as that
which would be produced were there
no atmosphere, by rays proceeding
from a higher star. we locate the body
in Il more elevated position than the
one which it actually occupies. Put a
dime on the bottom of a pail filled with
water and you have like conditions
with a similar effect. If you place
your hand where YOU think that YOU
see the coiu you will not touch it, but
a spot perhaps an ineh above the true
bottom. Again. do You notice how
steadily Venus shines? fyou are here
an hour later. when the stars are all
out, YOU will observe that all those
extent, are merrily twinkling. This
,,,o,lo f,,,> Ill &c -.
by the old nursery rhyme. Twinkle,
twinkle, little star,' is mot noticeable in
the case of any planet except Mercury,
and has been u subject of much study
on the part OF scientific men; it now
generally believed that it arises from
the Unequal bending of the rays Of
light as they pass through aerial eur
rents of different temperatures and
densitics. The facts seem to support
this theory, for where the air is the
densest-near the horizon--the effect
is most noticeable, where it is the
rarest-in oHr zenith-it is less marked
This twinkling produces another
illusion. When we look ut the heavens
on clear winters night the first inn
preston on our mind is that we see IN
almost infinite number of stars. In
truth seldom can an ordinary eye dis
Germ more than 1000 at once. If you
should observe the sky nightly for a
whole year there would he presented
to your view only about 5, 600. But if
you take telescope as Sir William
Herschell did, and point it toward that
portion of the milky way which looks
the whitest and the milkiest, you will
see more than 600, 600 stars pass across
the field of your instrument every fifteen
minutes"