Evening star., 1950-10-25
Most Remote of Planets
Measured by Telescope
Mount PoIomur Scientists
Report on Pluto Findings
By Thomos R. Henry


An apparently accurate measurement
of the diameter of Pluto, most remote Of
the planets, has been made with the 200
inch Mt. Palomar telescope.
This outermost of the suns family
approximately $3.50 100000 miles from
the sun itself and more than 3,500,000,000
miles from the earth-has been the sub
ject of many differences Of opinion among
astronomers.
It now can be considered as having q
diameter of 46 that of the earth, says
DR.. Gerard P. Kuiper, director of the
Yerkes and Mcdonald Observatories of
the University of Chicago. This places
it about midway in size between Mars
and Mercury.
This makes both its volume and mass
about tenth that Of the earth. 1t must
retain, DR.. Kuiper believes, some traces
Of an atmosphere. At the best, however,
this could not be more than hundredth
part the atmosphere of the earth.
Temperature Estimated.
1t is easier to estimate the temperature,
due to the enormous distance from the
sun, the planets only possible source of
heat. This cannot be more than from
40 to so degrees above absolute zero.
This is -459 Fahrenheit, the limit of
cold and the temperature of outer space
where all molecular motion starts.
Under these conditions Pluto hasn't
much to offer for those who believe that
flying saucers come from some other
planet which is the abode of intelligent
life. Its reflected light is about that
which would come from a snow-covered
surface. 1t hardly can be assumed that
the planet is covered with snow, as the
term is understood on earth. 1t is highly
improbable, however, that any of its
rocks are visible.
The mass determined for the outer
most planet is far from sufficient to
account for the gravitational attraction
exerted on the great planet Neptune from
that direction. 1t was this attraction
that led to the assumption of Pluto's
existence long before it was discovered
mass about 10 times that of the earth
Is required. There may be other planets
still more remote.
The diameter measured with the Mt.
Palomar telescope, DR.. Kuiper says, is
almost certainly accurate to within about
five per cent.
The day-the time of the earth's rota-
ton on its axis-varies by about a
thousandth of second each year.
This fluctuation has a pendulum like
periodicity. according to a report Just
made to the Royal Astronomical Society
by DR.. H. F. Finch of the Greenwich
Observatory. He used both British data
and observations of the Naval Observa-
tory in Washington, the time-keeper for
the United States.
According to the observations. the
time of rotation decreases from Janu-
ary through April, increases in late spring
and early summer, decreases in late sum-
mer and increases again from September
through December. Despite the SEEM
1ngly lnf1niteSimal time period involved,
DR.. Finch says, it is well within the
limits of accurate measurement with the
battery of quartz crystal clocks now set
up at Greenwich. The fluctuation has
been suspected for years. Recently Ger
man observers reported about the same
cycle.
It long has been recognized that the
rate of the earth's rotation is not abso-
lutely constant. It is gradually slowing
down due to the drag of tides on the
bottoms of shallow seas. It also is subject
to sudden fluctuations, all extremely
minute, Wnlcn are Unexplained and are
significant chiefly because of the time
keepers penchant for absolute accuracy.
Despite all this, the earth remains a
fairly good time piece for all practical
purposes, although by no means as accu-
rate as the atomic clock recently built
at the United States Bureau of Stand
ards.
At least tentative explanation now
can be offered for the period f1uctuation,
DR.. Finch says. 1t recently has been
demonstrated that there are great sea-
sonal shifts of air masses between the
hemispheres which result in changes of
pressure over the planets surface. The
time cycle seems to correspond with these
shifts, leading to the supposition of some
sort of cause and effect.