Evening star., 1939-09-09
Of Stors, Men
And Atoms
Notebook Of Science Progress
In Field, Laboratory
And Study

III uSlOS 6OOVIOlVIy
And Study
By Thomas r. Henry.
At least half of creation is dust.
It outweighs all the stars-30 or 40
billions Of them-and all the planets
comets and meteors.
This dust Is generally invisible and,
up to a few years ago its existence was
not suspected.
Cosmic dust reveals itself in three
ways, says DR.. Theodore Dunham, jr.,
Carnegie Institution of Washington as
tronomer. On rare occasions, he says,
1t may be seen directly when illuminated
by the intense light of neighboring
star. Its presence may be deduced by
the blocking out of the light of the stars
behind it. In very finely divided par
as light from the setting sun is red
dened by dust on its long journey
through our own atmosphere.
Says DR.. Dunham:
THE detection of free atoms of gas in
space depends entirely on the spectro-
scope, except for rare instances, such as
the Orion Nebula, where hot stars cause
the gas to f1uoresce and become lumin-
Gus. With the spectroscope it is possible
to detect In detail changes which have
occurred in beam Of light while travel
ing through space for hundreds or thou
sands Of years in coming to us from the
stars. The effect of interstellar atoms
Is to chisel out sharp lines in the colored
band Of the spectrum of distant star
These sharp lines match exactly the lines
absorbed by certain atoms inclosed in
tube with glass windows in our physics
laboratories, so that the identity of the
atoms in space can be clearly established
Sodium and ionized calcium have been
known to exist in interstellar space for
many years. About two years ago
bright alumnized grating ruled by Prof
R. w. Wood of Johns Hopkins University
was put into operation in a new type of
powerful spectrograph which had just
been developed 1T the Mount Wilson OBJ
servatory and Which was fed by starlight
collected by the 10O-inch telescope With
this equipment two additional elements
were discovered in space dn 1886 previ-
ously announced, potassium and titan
ium. OF even greater theoretical inter-
est is the recent discovery of an excess
sively faint line due to the atoms of
neutral calcium.
I'm space every atom is subjected to
a weak but incessant bombardment by
the light of the stars on all sides. The
ultra violet portion of this light tears
away from the atoms one, two or even
three of their outer electrons, leaving
them in a mutilated condition. Occasion
ally one of these ionized atoms, while
wandering through space, meets an elec-
tron torn from some other atom long be-
fore, and picks it up by electrical attrac-
ton, being thus restored to its original
neutral condition. An equilibrium is
reached between the rate of disruption Of
atoms by starlight on the one hand and
the rate of reconciliation of ionized
atoms with electrons on the other hand.
THE discovery of the neutral atom of
calcium is important because, when the
intensity of its weak line is compared
with that of the much stronger line of
ionized calcium, it shows just how far
the equilibrium has been driven in the
direction of ionization by the light Of
the stars, before the electrons in space
are able to hold back the disrupting
process. In recent investigation at
Mount Wilson the light of all the stars
has been added together for points at
intervals throughout the spectrum, max
ing due allowance for the increased alb
sorption OF ultraviolet light 1t has
thus become possible to calculate that
an average of approximately 1000 900
electrons must be present in each cubic
meter Of space between the earth and
the star in the constellation of Orion
The only reasonable source for such a
large number of electrons in space ap-
pears to be a nearly equal number of
atoms Of hydrogen, themselves ionized
to photons and electrons by the action
of ultraviolet starlight.
with these estimates of the number
VI clcCtiOIlS dIlu VI tIlc lIlIcIlSlly Oh SLdT-
light, the numbers of atoms of sodium,
potassium, calcium and titanium, both
neutral and once, twice and three times
ionized, have been calculated. Adding
together the figures for the ions of each
atom gives the total abundances for the
elements. The results are shown in, the
following table:
Average number of particles per Gu
bic meter in path between the earth
and the star in Orion
Electrons acknowledgements 1000, 900
Hydrogen atoms --------- 100000
Sodium atoms - $50
Potassium atoms ----
Calcium atoms - 3
Titanium atoms - O.O3
These figures are preliminary estimates
subject to extensive revision as the result
of further work. It is particularly i'm
portant to emphasize that the present
atomic census applies only to the space