The Appeal. [volume] (Saint Paul, Minn. ;) 1889-19??, 1922-06-10
DISTANCES OF !.
STARS MEASURED
New Method Being Employed by
Astronomers at Harvard
College Observatory.
BASED ON STUDY OF SPECTRUM
Vast Collection Of Photographs Nov
Being Used and Exact Figures
No Longer Depend on -. :.
{ p: .sstss Old System. Il

-
are now being measured for the first
time at Harvard College Observatory
by recently developed methods based.
upon a study Of the spectrum It has
been found that the huge collection
Of photographs Of star spectra, as
sembled at Harvard during the past
generation and numbering over 3OO,-
COO plates, can be put to new use
In determining the distance of stars,
and the work of measurement is. go
ing ahead rapidly. E~
Many Of the vast number Of stars
whose distances are still unknown are
the bright, comparatively nearby
southern stars, because nearly all the
observatories where stellar distances
are measured are located in the north
ern hemisphere. The Harvard astron-
omers are therefore concentrating
much of their attention upon photo
graphs of southern stars at the Har-
ward station at Arequipa, Peru.
.~. New Method.
The new methods of measuring the
distance Of star by a study Of it's
spectrum are based upon discoveries
by number Of astronomers. A re-
markable contribution to the subject
has been made by Dr. Neigh Mad Saba,
an East Indian, who is assistant pro-
fessor Of physics in the University Of
Calcutta.
Until recently the only available
method for measuring star distances
has been the parallax method, which
consists of triangulation, using the
line. In other words, observations Of
a star are made at intervals of about
six months. During this period of six
months the observer is carried by the
motion Of the earth to a point some
1856 million miles from that Of his first
observation, and using this distance
as a base line he can work out the
distances of the nearer stars.
Almost all the stars, however, are
so vastly remote from the earth that
even with a base line of 1856 million
miles their distances cannot be TRAN
gulated. XII .
It Is for these more distant stars
that the new methods are used. AT
the Mount Wilson observatory, w. 8.
Adams and his associates have sue
ceeded in developing procedure de-
pending on the lines in the spectra Of
stars as photographed with large tele-
scopes fitted out with powerful spec
troscopes. The lines are due to the
absorption Of light from. the stars
surface by the. clouds of iron, nickel,
calcium and other elements that form
it's atmosphere. DR.. Bertil Lindblad
has provided another method, based
upon the examination Of the so-called
"cyanogen" bands in the spectra.
These new methods have been care
fully checked by the older ones.
The Next Problem.
Now that methods Of measuring
star distances from a study Of spec
ira have been worked out, standard
lied and checked, the next problem is
to apply these methods to those thou
sands of stars whose distances are
still unknown. One of the funda-
mental tasks Of astronomy is to de-
termine how the stars are distributed
through space, and this can never be
known until the distances are meas
ured.
It is this task Of applying the new
methods for which the Harvard col
lection Of photographs Of stellar spec
ira has been found to furnish ex-
cellent material. To give a single ex-
ample, photographs made at Cam
bridge thirty-five years ago give the
distance Of Alpha Ursae Majoris, one
Of the pointers In the big dipper,
as about seventy-two light years. In
other words the light now coming in
from that star began its journey about
1850, and the light photographed on
the Harvard plates in 1887 started In
1916.