Evening star., 1939-12-14
Of Sturs, Men
And Atoms
Notebook Of Science Progress
In Field, Laboratory
And Study
By Thomas r. Henri.

BY Thomas r. Henry.
The whole Milky Way galaxy of 100,-
000,000,000 stars is revolving in a period
Of 207 100000 years..
All the stars are moving about a CEN
ter approximately 100000, ,0O0, 900 O0O. 900
miles, or $4,000 light years, distant from
the earth in the direction Of the con-
stellation of Sagittarius which is visible
in the southern Milky Way during the
summer.
The sun and its family of planets are
taking part in this titanic revolution at
a speed of approximately 180 miles per
second.
Such are the latest calculations of
astronomers of the Carnegie Institution
of Washington from studies of the
relative motions of stars in different
parts of the Milky Way at known dis
tances from the sun.
In such a system bodies closest tn the
center always move at higher speeds
than the more distant ones. An example,
where rather exact measurements can
be made, is the solar system. Mercury
is the nearest planet to the SUM- 1t
moves In its orbit at a rate of 80 miles
a second. Venus, which lies between
Mercury and the earth, has an orbital
speed Of % miles second. The earth,
about 23,0O0,OOO miles farther from the
center than Venus, has speed of 1875
miles per second. The outer planets
have still slower speeds. BY knowing
the rate of orbital motion it would be
possible to calculate roughly the dis
tance of any of the suns family from
the sun itself
The same is true of the galaxy itself,
where the place of planets is taken by
the far more massive stars. The center,
Of course, is not pictured as some ex-
treme massive body comparable to the
sun In the solar system, but as the CEN
ter of gravitational attraction Of the
whole system.
The stars used in calculating the dis
tance are, for the most part, those curl
Gus bodies known as Cepheid variables.
They are stars which vary in brightness
at a regular and periodic rate. The
brightness changes rapidly in periods
between 2 and so days. 1t has been
established that the period of light
change Is correlated directly with the
intrinsic brightness of the star. The
longer the period the more luminous
is the star.
If the astronomer knows the actual
luminosity Of the stellar body its dis
tance can be computed by comparing
this with its apparent brightness as seen
from the earth. The problem of galactic
motion has become one of studying more
and more of these stars.
The Carnegie astronomers now have
the data on 156 of these variables. They
are we'll distributed throughout the
Milky Way, except for certain southern
sections which can be seen only from
observatories located in the Southern
Hemisphere.
The underlying cause of Cepheid vari-
alton remains an unsolved problem. In
an individual cycle, Carnegie astrono-
mers explain, the light change shows a
quick rise to maximum followed by
more leisurely decline to minimum.
ASAOdoAlS SAAACilto "IoAA VIC oEOSt1 uElA
indicate that the stars atmosphere is
pulsating throughout the period and that
the greatest diameter is reached mid
way between maximum and minimum
light The changes in temperature and
color follow the changes in light. At
maximum light the star is whitest and
hottest and at minimum it is coolest
and reddest.
Among these Cepheid varables are
some of the most luminous and most
distant stars known. With a few excep-
tions they are located close to the plane
OF the Milky Way, and for this reason
their light is usually diminished and
changed in color by the clouds of absorb
ing material which are most abundant
in these same regions. The average
effect Of the absorption in the Milky
Way dust clouds is to reduce the appar-
ent brightness Of the stars by approxi-
mately one half in each $500 light years,
or the distance traversed by light NOV
ing at 10000 miles a second in this
period.
AS a result of this absorption most of
the known Cepheids in the Milky Way
galaxy are limited to regions within a
distance of $4,000 light years from the
earth. Since the center of the universe
is at more than twice this distance it is
extremely improbable that it ever can
be observed through telescope
Many hitherto invisible objects in the
Milky Way now are being photographed,
it is revealed by the scientific exhibit
now being arranged for the annual
meeting OF the directors at the Admins
tration Building, Sixteenth and P
streets tomorrow, and which will after
ward be opened to the public Photo
graphic emulsions with greatly increased
sensitivity to red light have become
available. Photographs of large areas
in the Milky Way show vast numbers of
red stars which were not visible on ex-
posures with ordinary blue sensitive
plates. The red sensitive plates are
effective in penetrating the heavily OBJ
scured regions. Several new clusters of
stars have been discovered in this way.
On account Of their sensitivity to the
light emitted by the red line of hydro
gen, the new emulsions give greatly in
creased prominence to diffuse nebulae
kL,a& Js-A~ k-S.k