Evening star., 1942-06-09
Of Stors, Men
And Atoms
Notebook Of Science Progress
In Laboratory, Field
And Study
BIZ Thomas r. Henri.

Astronomers have reweighed the moon
1t is about 1000 900 900 ,ooo 900 900 ton,
heavier than had been calculated In
the past.
The new determination will become
one of the fundamental constants in
the astronomy OF the solar system.
1t recently has been announced by DR.
H. Spencer Jones, astronomer royal of
Great Britain, to whom the Interna-
tional Astronomical Union assigned the
Job OF analyzing the immense volume
Of data gathered the world over in the
autumn Of 1881. when the tiny planetoid
Eros made its closest approach to the
earth in half century.
He and his associates at the Green
wich Observatory on the edge of London
have completed the task and a few
months ago announced that the sun
was more than 100000 miles further
from the earth than hitherto had been
supposed.
The new weight of the moon is the
second result of their work.
Eros is the earth's nearest neighbor
In space, except for the moon itself. 1t
Is little ball Of rock about II miles in
diameter. 1t has an extremely eccentric
orbit. In 1881 1t approached within
16,200,000 miles Of the earth, about T.
100000 miles closer than the planet
Venus.
The simplest way OF measuring dis
tances in the heavens Is by means of
triangulation, precisely the same as that
used by surveyors in determining dis
tances on the surface of the earth. The
diameter of the earth-or, in the case of
distant stars, the diameter OF its orbit
provides the known base Of an enormous
triangle whose apex is the heavenly
object. The nearer the object the larger
the angles. Hence the lengths of the
sides of the triangle can be determined
with greater precision.
The close approach of Eros offered an
almost ideal opportunity for such tri-
angulation. With the world at peace,
almost every observatory on earth
the heavens took pictures of the tiny
planet, carefully observing the time and
their own positions. At the most favor
able time the diameter of the earth
formed the base of a triangle which, to
an observer on Eros itself, would have
been half the length Of the diameter
OF the full mean
Astronomers OF every civilized nation
including. at the time, Germany and
Japan-agreed to turn their observa-
tions over to DR.. Jones.
The weight of the moon can be de-
termined by It's gravitational effects on
the earth and the sun and these depend
on distance. Changes in the hitherto
accepted scale of distances in the solar
system make the change in its weight a
matter Of course.
Essentially the earth weighs about 81
times as much as the satellite, once q
part Of the planet itself. which is about
10000 miles away. The weight of the
earth, as determined most recently by
gravitational measurements at the
United States Bureau Of Standards, is
about 5000, ,Ooo, ,ooo, 900 900 900 900 tons.
The chief difference brought about by
DR.. Jones calculations, astronomers ex-
plain, will be In the so-called mutation"
of the moon-the varying positions Of
its north and south poles through the
years due to the gravitational pull Of
the earth. which is greatest in the di-
rection OF its equator. This will make
a fraction Of a second difference in the
prediction Of the time of eclipses.
1t also changes the center of gravity
Of the earth system-which includes both
the earth and the moon. This is i'm
portant in astronomical calculations. 1t
is somewhere near the center OF the
globe. but the new calculations move 1t
a few miles nearer the surface.
The calculations also make everything
on the surface of the earth a trif1e
lighter than was supposed before. The
weight Of . man. for example, is actually
the gravitational pull upon him Of the
center Of gravity Of the earth-moon
system. With the change in position OF
this center Of gravity his weight changes,
although not enough to be detected by
any instrument.