Evening star. [volume] (Washington, D.C.) 1854-1972, 1928-07-29

100000 miles from the earth. Nov
1t is considered that the stars within
our range of visibility form a single
system 100000 light years in diameter
But there are many other such stellar
systems. Our own system Is called the
Galactic system, or system of the Milky
Way. II has definite limits and is
shaped like a thin watch, having a
thickness equal to about one-eighth of
its diameter. Some think 1t has a
spiral structure. and TO an observer on
distant planet Ii would look like the
spiral nehula seen in our own heavens.
The half dozen nebulae which are
nearest the Galactic system, including
the Magellanic Clouds, are at distances
ranging from 100000 to 100000 light
years. Their diameters range from
1000 to $4,000 light years. and their
actual brightness from 10000 900 to
l ,000, 000. 900. 900 times that of our sun.
The l00-inch rejecting telescope of
Carnegie Institutions Mount Wilson,
Calf. Observatory has pushed back the
boundaries of human visibility TO a
radius of 100000 light years. With
faster Photographic plates and Ia
telescopes, both possible. man will be
able to push these limits several times
farther back With improvements, IL
may be possible TO detect brilliant nehu-
lac at distance of thousand million
light years and to photograph them
with light that started on its Journey
when the earth itself was an infant.
In examining these nebulae. an as
tronomer peeps at scenes which &C.
Cured in the geologic ages The near
est universe to our Galactic system is
the Magellanic which our cameras
l. Ik~t@a f.fN
region 100000 years ago. We can see
them as they we're in the great ice age,
before the dawn of man Conspicuous
spiralS belong to the Pliocene Age while
those at the extreme limits of the OBJ
servable region are of the CarboniferouS
age
These Photographic records are fossil
records in sense, just as the dinoSaur
eggs found i'm the Cobb Desert. And 1t
is even suggested that the present APP
pearance of these distant bodies is de-
ceptive as they may have been de-
Stroyed since the rays of light started
on their Journeys many years ago
= y
IN exploring systems outside our own.
astronomers have perfected a meth
cd of gauging star brightness for deter
mining distances. BY comparing a stars
apparent brightness with what is be-
lleved to be its actual brightness one ar
rives at a fairly accurate estimate This
method is based on the assumption
that light having certain bright
ness at unit distance appears only one
fourth as bright at double the distance;
one sixty-fourth as bright at eight
times the distance one hundredth as
kvtr Of hN fvfa
on. Thus with the apparent brightness
and intrinsic brightness, IL has been
found possible to determine actual dis
tances
Ways of determining stars actual
brightness have been defined in the
last six years DR. Walter S. Adams of
the Mount Wilson Observatory showed
that when the light Of an intrinSically
bright star Is passed through a spectre
scope certain telltale lines in the spec
trum reveal good deal about the star S
luminosity. Some of these lines are
more intense than
others. DR.. Adams showed also that in
the case of weak stars, these character
iStic intenSitieS are reversed.
This method. found TO be accurate
for nearby stars whose distances arc
known. Is now accepted as reliable for
fixing the distances OF remote suns
A second important method Is that |
perfected at Harvard University OhServ- |
atory. Here It was observed that certain |
stars pass through definite periods of |
variation In which their luminosity be- |
comes more intense, then gradually |
weakenS, The periods range from less |
than one day TO 100 days, depending |
upon the individual star, II was noted !
that among these stars, all giant suns |
larger than our own, a definite relation. |
ship exists between their actual bright |
ness and the period of their variation /
The brighter the star The longer Il /
takes TO complete Its cycle
Recently, Carnegie Institution issued !
4 memorable atlas of selected regions