Evening star., 1929-12-15
Plumbing the Universe

and 1t Is not improbable that the great
open cluster of blue giant stars in Orion
is the remnant of a globular cluster
which invaded our system trillionS OF
years ago. Perhaps our sun belonged
at some time to an outside cluster, and
if so it travels now in the larger swarm
of the Milky Way because it is a cap
tive"
How can you tell the distance of
these remote bodies and their direction
and velocity of travel?" asked.
THE SpectroScope is our great ally in
studying Velocities and motions. 1t
breaks up starlight into the familiar
band of rainbow colors, ranging from
violet on one side to red on the other.
If the spectrum of star shows shift
ing of its lines toward the red side, we
know that the star is moving away; If
the shifting is toward the violet, we
know it is approaching. The amount
Of this displacement of lines, deter
minded micrometrically, indicates the
velocity.
when it comes to measuring dis
tances beyond 5000 light-years, our
most dependable yardstick is a peculiar
class of variable stars known as
Cepheids. They are called that because
the first to be discovered is in the con-
stellation Cepheus. We have cata-
logued more than 5000 Cepheids and
discovered many last year.
"Cepheids are peculiar in that the
period of variation for each star is an
indicator of its real magnitude. Thus
Cepheid which requires IL hours to
change from its maximum brightness
through minimum and back to maxi
mum has a real magnitude 100 times
that of the sun. One that has period
of 40 days is 10000 times the suns
magnitude.
Astronomers Standard Candle.
"The Cepheid has become the astron-
omer's standard candle. Whenever he
sees one he has only to time its period
of variation to determine its distance.
"Cepheids are scattered through the
Milky Way and have proved of i'm
mense help in gauging the form and
dimensions of our galaxy. We have
found Cepheids in the globular clusters
and In other outside bodies"
The richest mine for the discovery of
CepheidS, however. has been the Ma
gellanic Clouds, two great, brilliant
patches of stars which rotate around
the South Pole and are visible only in
the Southern Hemisphere. The third
research in DR.. Shapley's program Gen.
tiers on them.
we are interested in the Magellanic
Clouds" he explained, because they
are outside systems, entirely independ-
ent of our galaxy, and yet are near
enough to be resolved into individual
stars and studied in detail. The Ma
gellanic Clouds are about 100000 light
years distant. They are island uni
verses and are receding from our posi-
ton at velocity exceeding 100 miles
a second.
"All the different kinds of stars that
go to make up our Milky Way are
found In the Magellanic Clouds. They
contain both dark and luminous nebu-
lac, giant blue stars, red stars and
Cepheids, which are yellow giants.
I'VE are building 60-inch rejecting
telescope which we expect to install at
Harvard's new station in South Africa.
We will use it mainly for photograph
ing the Magellanic Clouds"
The fourth line of attack on the
mystery of stellar organization and dis
tribution is aimed at the even more
distant island universes, the spiral neb-
ulae. These differ from the Magellanic
Clouds in that they are more uniform
in shape, appearing. indeed, like great
pinwheelS of light. One of these out
side univerSes can be seen with the
naked eye-the great nebula in An
dromeda-but research indicates that
it is the largest and nearest, being only
100000 light-years away. Cepheid va
riable stars have been seen in this
nebula, and indubitably Ak its distance.
1t is estimated that there are more
than a million of these galaxies, and
many of them are many millions of
light-years distant.
Boundary Is Great Problem.
zone of the great problems, said
DR.. Shapley, ''is the question of how far
space extends. Has the universe a
boundary? Before Einstein propounded
his theory of relativity we were more
prone to think of the universe as limit
less. Exceedingly few astronomers to-
day would say that it is. Yet the answer
has not been proved experimentally-
it is all still very much in the air.
But we have this situation: The prin-
ciple of relativity has been verified by
certain astronomical tests, and we shall
never go back to our old ideas of abso-
lutte space and time Starting from this
general principle, however, there are
different forms that cosmogony may
take. One form is the universe as de-
deducted by the Dutch astronomer De
Sitter. He made some brilliant deduc-