Evening star., 1924-09-21
How Hot Are the Stars?
WHEN such a question is answered

NIHEN Such a question IS answered
w by layman, quoting some
book on astronomy, he is met with
incredulous looks and sometimes with
such a remark as: 1T is impossible e
for anybody to know such things"
But one OF the great astronomers
OF the world, Nordmarn, to whose
experiments is due the definite
knowledge we have Of the age and
heat of the distant stars. has told
just how their age is computed and
how the thermometer is applied to
them.
It is easy to see at once that what
is called the age of the stars, in
other words, the more or less ad
vanced state Of their development,
is related to their temperature. La
place demonstrated, and all modern
researches have but confirmed his
conception. that this modest star
which is our sun has been formed
by the gradual condensa ton OF a vast
rebula composed Of very rarefied
gases, and which at its beginning ex-
tended to beyond the orbit Of Neptune.
In the sky are to be seen a fairly
large number of these nebulae in a
state OF more or less advanced con-
Gensation, and this should suffice to
prove that the different stars have
doubtless widely differing ages. We
know in addition that the gases of
the nebulae are very cold, and Helm
holtz has proved that when a mass
of nebular gas condenses its heat
gradually increases through the sole
effect of the fall of matter toward
its center.
But this heating has a limit, and
when the gaseous mass has become
sufficiently small and dense so that
the gases can no longer move about
with ease, calculation shows that the
heat gained by condensation then be-
comes less than that which is lost by
radiation into space, and the formed
star begins to cool.
From this IT follows that the tenn
perature of a star from the begin
ming of its formation gradually in
creases, attains a maximum, then di-
minishes to the point Of coldness and
to that complete extinction Of which
the dark satellites Of certain stars
give us examples.
Now, we know that the sun is a
star denser than Sirius; that is, more
advanced IN its development. To
calculate the exact position of the
sun 1t will suffice for US to ascertain
whether Sirius has a higher or a
lower temperature than tho sun. In
the former case it will evidently
follow that the sun is star In it's
decline, tending to complete coldness-
In the latter case, on the contrary, 1t
would be a star relatively young and
destined in the course Of centuries to
become much hotter than 1t Is today.
Now, this important question, which
Is closely attached to the future Of
= our earth, it has been possible to
solve, as we are now about to see.
Ordinarily thermometers can give
only temperatures Of bodies with
which they are placed in contact.
Evidently, therefore, they cannot be
used for the sun, since the latter is
s2.00o000 miles from the earth; so it
has been necessary to seek another
method. The science of pyrometry
cessibfe objects was created when a
blacksmith first had the idea Of put
ting near his cheek the hot iron the
temperature Of which he wanted to
judge. And it is by procedure
analogous in principle. though neces-
sarily little less rudimentary in its
application, that the temperature OF
the sun has been measured.
By means of a special apparatus
called actinometers it has been proved
that the quantity of radiant heat that
ceives from the sun at the zenith is
equal to about 10000 great calories
per minute. A great calorfe Is the
quantity of heat necessary to raise
one kilogram Of water one degree
tCentiErade) in temperature. It fol-
lows that if the earth were enveloped
in layer of water 20 centimeters
thick placed at the limits Of our
atmosphere, which would Be able to
atAp all heat the sun sends us, this
vaIer would all be raised in one
minute from the temperature of ice to
that of boiling water.
Taking into account the distance OF
the sun, it is calculated that the
total quantity Of heat which this
sends into space in one year is equal
to the enormous number of almost
three decillons of great calories
That is a number which takes 35
.'naughas" to express!
Finally, from these. data it can
easily be deduced that the tempers-
ture of the solar surface is some
where between 5000 degrees and
10000 degrees Fahrenheit. Let US re-
call in this relation that the highest
temperature which has been realized
on earth, that of the positive crater
of the electric arc, is not above e,332
degrees Fahrenheit.- - ---- ---