Democratic Northwest. [volume] (Napoleon, Ohio) 1869-1894, 1890-07-03
WHY THE SKIS BLUE.
VARIOUS PROMINENT HEAVENLY
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Atmospheric Reffaction and Modi.
fcation-Enect OF the Mipgiing of
Rays-The Pretty But Deceptive
Twinkiing Star.
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"You have all noticed, ;" said the pro-
fessor, "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, espec-
tally when, after sunset, we look toward
the western horizon, the color Is o yell
lowish red. With the spectroscope it
can be shown that the white light from
different eolored rays. Indeed this can
be shown by means of any triangular
prism, say one of the pendants of a
path of beam of light will project on
a screen a band Of seven colOrs-red,
orange, yellow, green, light blue, dark
blue and violet. Understanding this
we can readily see how the effect is
blue when piece OF blue glass is inter-
posed, or red when red glass is used.
| All DuI ttIt Uluc anu fcu rays IccDCCk-
lively 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 sunlight.
What has this to do with the sky col
ors? will now show you. Dissolve
little white CASTLE soap in tumbler of
water, so as to make the water slight
ly turbid. Place 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
! 1t next in direct line 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 water, refract
blue light; while the background of
darkness surrounding the earth replac-
ed the black screen. The atmosphere,
like the solution of soap and water,
transmits yellow and red rays but
slightly refracted, while the blue, being
a weak color, IS refracted to low to be
seen, hence when we look toward the
source of light in the evening or morn
ing the sky is ofa yellowish red color.
This effect is more pronounced then
than during the day, because when the
sun is near the horizon the rays travel
agreater distance through the air in Or
der to reach the earth then when di-
rectly above us. Consequently the
blue rays are more thoroughly refract-
ed.
"The atmosphere has many effects
in modifying the appearance of the sky
and the heavenly bodies. Look at Ven
us over there near the western horizon
and just below the crescent moon,
which has come into plain view while
we have been talking ION account of
the deepening darkness). Its real dis
tance from the horizon is not as great
as it appears, for the rays of light
which it reflects to US and which it re-
ceives from the sun are bent downward
when they pass into our air, perhaps
fifty miles from the earth's surface.
"As the effect is the same as that
which would be produced, were there
no atmosphere, by rays proceeding
from higher star, we locate the body
in more elevated position than the
one which it really occupies. Put a
dime on the bottom of pail filled with
water and you have like conditions
with a similar effect. If you place
your hand where you see the coin you
will not touch it, but q spot perhaps an
inch above the true bottom. Again, do
you notice how steadily Venus shines?
IF you are here an hour later, when the
stars are all out you will observe that
all those near the horizon, the others to
a smaller extent, are merrily twinkling,
This appearance, made familiar to all
of us by the old nursery rhyme,
'Twinkle, twinkle little STAR" is not
noticeable in the case Of any planet
except Mercury, and has been a SUBJ
lject of much study on the part of fscien-
tific men; 1t is now generally believed
that it arises from the unequal bend
i ing of the rays of light as they pass
through aerial currents of different
temperatures and densities. The facts
seem to support this theory, for where
the air is the densest-near the horizon
the effect Is noticeable, where it is the
: rarest-in our zenith it is less mark
ed.
"This twinklIng produces another
illusion. When we look at the heav-
ems on a clear winters night the first
impression on our mind is that we see
an almost infinite number of stars. In
truth, seldom can an ordinary eye dis
Germ more that 1000 at once; if you
should observe the sky nightly for a
whole year there would be presented to
your view only about 5000. But if you
take telescope, as Sir VIM. Herschell
did, and point it toward that portion of
the milky way which looks the whitest
and the milkiest, you will see more than
600,0 900 stars pass across the field of your
instrument every fifteen minutes."-
Cincinnati 7smes-Stdr.