Evening star., 1901-10-23
STELLAR VELOCITIES
SPECTRosCOPIC WORK AT THE LICK
OBSERVATORY.
Capella n Double and POIaris a Triple
Star Groombridge's
"Runaway."
From the New York Tribune.

From the New York Tribune.
Those who have followed the work done
at the Lick observatory within the last
few years, recall the measurements of We
locities made by Prof. w. W. Campbell
with the Mills spectrograph. From Study
of the displacement of lines in photogra phs
of star spectra it has been possible to tell
approximately how rapidly certain celestial
bodies were approaching or going away
from the earth. 1t is only motion in the
line of sight which is thus discernibe
That which takes place at right angles
with this direction is known as proper
notion and, if considerable, can be ascer-
tanned by noting a stars change of appar-
ent position telescopically.
When a star exhibits a double spectrum
and some of it's lines displaced to the
right while others are shifted tc the left
it is recognized as a double. One of the
twin bodies is moving away from the. earth
and the other toward us when that phe-
nomenon rs observed. This is on,y tenn
porary situation, though, Since a true
binary system both bodies are moving
about common center in circular CT clip
tical orbits.
CapeIIa's Character.
In a bulletin recently issued by Prof.
Campbell additional information is fur
nished in regard to Capella, whose, double
character was announced from the Lick
observatory two years ago. The two mem
bers of this pair seem to be nearly equal
in mass proportions between them being as
1.26 is to l. The bigger one belongs to the
solar, pale yellow, type Of star, while
the smaller is between the solar and Sirian
types. Sirius is a pure white or blIis1
star, and some astronomers believe that
bodies of this class are hotter than the vel
low stars. But upon that point stellar spec
troscopists are not now nearly so un2ni-
nous as they were twenty years ago. V1s-
ually theprincipal star of the pair is about
one magnitude brighter than it's companion.
but photographically they are more closely
matched.
The period required by the two compo-
nents of Capela to traverse their orbits
has been found to be 104.1 days, and a
rather abstruse calculation of the distance
between them gives S5,000O00 kilometers, OF
"a 600 600 miles. If the smaller body passed
directly between the larger one and the
earth while making it's revolution there
should be a trifling yet perceptible diminu-
tion of Capellas light every three and a
half months. But careful watch has failed
to reveal any such effect. 1t is therefore
probable that "the orbit plane makes an
appreciable angle with the line of sight"
spectroscopic binaries. Indeed, there is
only one star visible in the northern heav-
ems which is distinctly more brilliant, Sirius,
though Vega and Arcturus closely rival II.
Capela now rises well up IN the northeast
in time to be conspicuous in the late even
ing. Aldebaran, being redder, fainter and
further south, cannot we'll be mistaken
for it.
Notes on Polaris.
The triple character of Polaris, suspected
for several months is now formally con-
firmed by Prof Campbell. While it's ma
ture has been discovered by the spectro-
scope the evidence is different from that
by means of which "spectroscopic binaries'
are identified. There are not three separate
spectra whose lines shifted in different
directions at intervals. There Is only one
light emitting object In the group. But
inequalities in the velocity with which this
recedes from the earth pointed to the fact
that Polaris has a dark companion, prob
ably a moon which revolves with it around
a common center. The period of this mo-
ton is-three days, twenty-three hours and
fifteen minutes 1t was more complicated
and a slower task to secure proof that the
pair is moving about another comparatively
distant center, in combination with third
body, which is also non-luminous. The pc
riod of this second movement is not yet
stated but Professor Campbell declares
that the reality of the phenomenon Is no
longer doubtful
The largest apparent movement at right
angles with the line Of sight which was
known for many years was that OF Star
No. / $50 in Groombridge's catalogue. By
Ball and others it has been called the run
away star Its proper motion amounts to
705 second of arc annually. Coupling this
fact with Newcomb's estimate of the dis
tance of Groombridge $50, Professor
Campbell gets $50 miles a second as its We
locity at right angles, with the line of sight.
The director of the Lick observatory has
now, with the aid of the Mills spectrograph
made a computation of the motion away
from the earth and this he puts at fifty
eight or sixty miles second.