Evening star., 1939-05-20
Of Stors, Men
And Atoms
Notebook Of Science Progress
In Field, Laboratory
And Study


In Field, Laboratory
And Study
By Thomas r. Henry.
1t is approximately 1se24o,oo0, ,ooo.-
100000 miles to the hidden center Of
our system Of stars.
This measurement, Of fundamental
significance in the surveying OF creation,
has just been reported to the National
Academy Of Sciences here by DR.. Harlow
shapley. director Of the Harvard Uni
versity Observatories, based on his OBJ
servations of variable stars in front of a
window in the sky.
DR.. Shapley actually determined the
distance as somewhere between 8h and
II kiloparsecs A kiloparsec is a thou
sand parsecs The parsec, about 49,
100000, 100000 miles, is the basic unit of
astronomical measurement when the
vast sweeps of celestial space are consid-
cred. Starlight coming to the earth
from the neighborhood Of this center is
a little more than $4,000 years on the
way. If newer methods OF photography
ever penetrate this dark region, they
will record what was happening there
about 10000 years before the dawn of
recorded history.
His new measurement, DR.. Shapley
says, Is essentially in agreement with
recent estimates based on mathematical
computations Of the dynamics of our
great star system and the distributions
OF certain types Of star clusters. But In
spite OF the vast distances involved in
the new measurement, the Milky Way
galaxy becomes a smaller place and the
earth much closer to the center of things
than astronomers had calculated In the
past.
DR.. Shapley's estimates are based
largely on sky photographs made with
the most up-to-date equipment at the
Harvard Observatory at Bloemfontein,
South Africa. where special studies are
being made Of the sky in the Southern
Hemisphere.
Like a titanic pinwheel the 30OO0,-
600 y0OO-star Milky Way galaxy revolves
around a hub-actually a theoretical
point which is the center Of its gravita-
tional forces-located somewhere in the
neighborhood Of the constellation of
Sagittarius the Hunter, in the southern
sky
The center itself is hidden from direct
observation by cosmic dust clouds. The
light of stars and star clusters in the
neighborhood comes through to the
earth very family. This formerly led
to the conclusion that they were much
more distant than they actually are, and
that consequently the Milky Way galaxy
itself was the giant of creation compared
to the hundreds of thousands of similar
galaxies that lie beyond it across mil
lions of light years of empty space.
TWO years ago DR.. Shapley an
nounced the discovery of window in
the sky" through which astronomers
could look out Of the galaxy itself with
relatively unobscured vision. This was
a wide patch in the southern heavens,
photographs of which revealed an ex-
ceptlonal number of so-called spiral
nebulae, now known to be other galaxies
comparable in size to the Milky Way
system. Either more are actually locat-
ed in that direction or it is easier to see
them, DR.. Shapley reasoned. The first
hypothesis indicated a lop-sided uni
verse, in contradiction to other evidence.
The other hypothesis, now accepted, was
that there is less light-obscuring dust
between the earth and extragalactic
space in this direction.
NOW this window. he points out in his
report to the National Academy, lies in
the general direction Of the center of the
universe and, celestially speaking, is not
very distant from it. Besides the ex-
traordlnary number of outside star sys-
TENS visible in this direction DR.. Shap-
ley's observations showed more than 800
variable stars whose light grows brighter
and DINNER in regular rhythms. More
than half OF these are the so-called
Cepheid variables, now used universally
by astronomers as space measurers for
great distances
The period of such a star, it has been
determined, varies with its brightness
Hence, the actual brightness Of such a
star anywhere in the universe being
known, 1t is possible to determine its
distance from its apparent brightness.
providing that the light is coming
through a complete vacuum. Actually
such condition does not obtain any
where, for the universe is all cluttered
up with clouds of dust and debris, the
rubbish heaps of the star builders.
But in this direction, DR.. Shapley con-
cluded, there is very little obscuring
matter since the eye of the telescope
could see out of the galaxy itself into
1ncomprehensible vastnesses of space.
The Cepheid variables, however, are
parts of the Milky Way galaxy itself,
lying between the earth and the bound
aries OF the great star system. Their
light, however, is coming over the same
unobscllred path as that from the outer
galaxies. Hence, 1t could be assumed,
their apparent brightness affords a
fairly accurate measure of their distance.
The next step was one Of comparison
with the brightness of the Cepheids lying
IN the direct path to the center OF the
universe The distribution of stars pre-
sumably is essentially the same in
all directions away from the hub.
Their DINNER apparent luminosity was
matched with those of the similarly dis
trlouted variable stars in the direction Of
the window Tn this uov tho thickpoec