Evening star., 1925-10-18
SCIENTIST LISTING
RUNAWAY STARS"
Variable Luminaries, Bright,
Then Faint, Discovered by
University Professor.

WILLIAMS BAY, Wis, October
lI.-RunaWay stars and new variable
stars that periodically become bright
and then faint are being discovered
by Prof. Frank +. Ross of the Yerkes
Observatory as "a result of the study
servatory's files. Various fields of
stars. largely in the Milky Way, were
photographed some 20 years ago by
the late Prof. L. T.. Barnard, who
used thu Bruce Photographic tele-
scope. This instrument is a camera
with several lenses, the largest 10
inches in diameter, and it is mounted
so as to follow the stars in their
apparent daily motion across the sky.
Thus these photographs show the sky
as it appeared about two decades ago.
To discover what has happened in
the interval. Prof. Ross is comparing
them with similar photographs
which he is making of the same
regions through the Bruce telescope.
Rare Instrument Used.
To compare two pictures. each
showing thousands of tiny dots
representing stars, all but half a
dozen of which are precisely the
same, and to locate the ones that
have moved or otherwise changed in
the interval would seem like a hope
lessly complicated task, but the use
of an ingenious instrument known as
the blink microscope makes 1t rela
lively easy. This consists of what
might be called a double periscope.
One photogra phic plate is placed at
each end. By oscillating small
lever :he observer can see first one
and then the other In as rapid sue
ceSSion as he desires. The stars that
a
no change in appearance, but If one
has moved between the two eX-
poSureS 1t seems to dance to and
fro as the lever Is moved. If a star
has varied in light, the image dot
seems to grow larger and smaller,
while If a new star has burst out, its
image will appear and disappear.
So far, Prof. Ross has examined %
pairs of plates in this way and has
found more than $50 rapidly moving.
| or proper motion stars, and 40
variables that were not known before.
Some of the proper motion stars are
moving faster than two seconds of arc
a year. which in about 900 years would
take them over a distance equal to the
moons apparent diameter in the sky.
This may not seem very rapid, but the
most rapid star in the sky known to
astronomers, which was also discover
eu DN fTOI- Bar Is lllONIlS dl
only about five times this speed. And of
the countless legions Of stars only
about 200 have been known up to the
present that move faster than one
second of arc a year.
Measure Motion Only.
But these plates only measure mo-
ton across the sky, and if a star hap
pens to be moving directly to or from
the earth, its motion will not be APP
parent. Such motion, called '.radial
velocity" may be detected by analyz-
ing the stars light in spectroscope,
for the light waves are crowded to-
gether from an approaching star, and
spread out If it is receding. a similar
effect makes a fire engine bell, for eX-
ample, seem shriller when coming
toward one than when going away.
For three nights a week, when
weather permits. the great 40-inch
refracting telescope at Yerkes, the
largest of it's kind in the world, is
used to make these spectrum photo
graphs. This work was begun by
Prof. Edwin B. Frost, director of the
observatory, and is now being carried
on by Prof. S. B. Barrett and DR.. Otto
Struve. DIR. Struve is a young Rus
sian astronomer and belongs TO the
third generation of famil yof astron-
omers that includes some of the best
known names in the history of the
science.