Evening star., 1953-01-16
Moons fCout of Dust
Is Perfect Insulation
Naval Astronomers Guuqe
Its Heat by Rudio Waves

Naval Astronomers Gauge
Its Heat by Rodio Waves
By Thomas R. Henry
The moon wears heat-proof, cold
proof overcoat of dust
theoretically on its light side, ex-
posed constantly to the full head of
the sun. it should have temperature
Of about 400 degrees above absolute
zero, far above the boiling point Of
water The temperature of it's dark side
should be about 100 degrees above abso-
lutte zero, almost the cold of outer space.
Quite different is the story revealed
to Naval Research Laboratory astron-
omers by the new radio astronomy, de-
lection and Interpretation of short
radio waves received from the moon.
Such waves come from any body whose
molecules are moving-that is, any,
thing above the temperature of absolute
zero. They indicate, with considerable
accuracy. the heat Of their source.
The moons radio messages, as de-
scribed by DR.. John P. Hagen of the
Naval Research Laboratory, indicate a
constant temperature of about $50
above absolute zero, In sunshine and
darkness.
The explanation for this, Dr. Hagen
says. Is fairly simple. The surface Of
the moon must be covered by a fairly
thick layer Of fine dust. It provides al
most perfect insulation. Almost no heat
can get in or out. Existence of such a
dust coat previously has been postulated
on other grounds.
No Atmosphere.
The radio measurement also makes it
certain that the earth's satellite exists
in what is close to an absolute vacuum.
1t has not a trace Of anything COM
parable to the earth's atmosphere.
The origin of the moon has been
considerably debated. A common
theory is that it was once part of the
earth and was torn loose in some
cataclysm two or three billion years
ago, leaving the present basin of the
Pacific. Presumably it is made of pre-
cisely the same materials as the earth
and may have carried some of the
earth's atmosphere with it. It was far
too light a body, however, for its
gravity to hold this atmosphere for
more than few years.
Consequently it receives the full
force of the suns radiation. The
earth's atmosphere is opaque to most
of the energy sent out by the sun.
Only visible light and short radio
waves, the basis of the new astronomy,
get through.
Without any shielding atmosphere
the moon surface is bombarded con-
stantly by meteoriteS, the shooting
stars, Of which millions hit the outer
atmosphere of the earth every day.
They are burned up passing through
the outer levels of the atmosphere.
On the moon such a bombardment
over two or three billion years pre-
sumably is responsible for pulverizing
overcoat.
Not Entirely Dead.
Thus the radio astronomers have
demonstrated that the moon is not
yet entirely dead, although the process
apparently is in the direction Of even
tual loss of all its heat.
Obviously the radio emissions from
such cold body are very feeble. They
can be detected only when the Naval
Research Laboratory's great dish
shaped aluminium antenna, so feet in
diameter and the second largest in the
world, first is turned on the night sky.
This sky has certain constant ennis
sion. This is compared with what is
received when the dish" is turned on
the moon.
While exceeded in size by one an
tenna in England, the giant in WASH
ington has by far the SharpeSt beam
and is being used chiefly to study the
radio emissions from the sun. With
other apparatus only the output of the
whole sun can be obtained. This one
makes it possible to isolate the mes
Sages" sent out from about one-eighth
of the solar surface. Hence the solar
disk can be scanned daily for varia-
tions-Such as radio emissions which
are found in the vicinity Of sunspots
and solar flares.
In this way it is possible to deter
mine the heat of different layers Of
the sun. This already has led to the
surprising finding that the corona. the
pearl-colored ring around the sun seen
during q total eclipse, has q tempera-
ture of more than l million degrees r.
This temperature decreases at greater
depths in the suns atmosphere. The
temperature of the visible surface, for
example, ranged from 5000 to 10000
degrees.