Evening star. [volume] (Washington, D.C.) 1854-1972, 1926-06-27
THE STARRY SKIES IN JULY
by PROF. SAMUEL G. BARTON
or the University of Pennsylvania.

Last month we discussed briefly our
dependence upon the sun for light
and heat and some of the ways In
which we recognize the debt by our
language. often unconsciously. We
will now consider the graVitational
tie which keeps us from losing those
benefits. The earth in a year moves
around the sun In mighty orbit
about 5S4 900 900 miles In length. The
path is very nearly circle of $4,000
600 miles radius. with the sun about
800 900 miles out OF the center We
are farthest from the sun on July ..
at a distance Of "a. 500. 900 miles. jan
uary we are 91,34O. 900 miles away.
which Is the least distance. The varia-
ton in distance causes only about 3
per cent varia ton in the amount of
light and heat.
Many are puzzled as to what mNs-
terious force keeps the earth thus
moving in its orbit perpetuallN. Sci
entists know we'll that no force at all
is necessary to maintain motion.
Motion is a more natural state than
action of force when either the
rapidity OF the motion or its direc-
ton changes. Since the direction and
rapidity of the earth's motion are con-
stantlN changing. there is evidence
nf Il force. II Is a great force directed
toward the sun. We call it the sun 5
attraction What this force is no one
knows. 1t is as mysterious to the
scientist as to the layman. Giving 1t
Il name in no way explains II. 1t is
Just as true that the earth attracts
the sun, bat as the sun Is $685. 900
times as assi.e as the earth its in
fluence on the earth is that much
greater than the earth's influence on
the sun.
The force holding the earth To the
sun is equivalent to the weight of 80
,tuintillionS Of tons t36 followed by
u ciphersl. To keep the earth in It's
path, If there We're no attraction. we
should require a rod OF the very best
steel 5000 miles in diameter: that IL
a seventh as large as the earth itself
in cross.section. How such stupendous
forces can act across space from one
body to another without any apparent
material connection is an unsolved
mystery unless it is really explained
by Einsteins theory 1t Is called "ac-
ton at a distance"
When the moon comes between the
earth and the sun it cuts off the suns
light and heat, but the sun s attrac-
ton for the earth is in no way af-
fected. This again is mysterious.
Should the suns attraction sud
denly cease the earth would keep on
moving In the direction in which II
was moving at the time. with the
same velocity. The direction of its
motion would be that of the tangent
to the orbit and its velocity 1912
miles second the rate at which il
moves in its orbit. Since the tangent
Il perpendicuiar tu In" direction of
the sun. the earth would leave the
sun Very SLOWLY at first. In the first
second ii would rtcede only One-ninth
OF All inch. Each second thereafter
IL would leave the sun more rapidly
until ii reached the maximum OF lS.o
miles d second. which was its velocity
in space all the time. In as years II
would have reached the distance OF
Neptune from the sun. but long before
that time the temperature would have
fallen 10 such a point that life on the
earth would have persisted.
One may ask why. if the suns Al
traction is so very powerful. it is not
quickly pulled into the sun. If 1t
were not revolving in its orbit il would
he II its orhital snotion we're sud
denly stopped it would fall ne-ninth