The evening times. [volume] (Washington, D.C.) 1895-1902, 1901-11-02
VELOCITY OF THE STARS.
How Near and How Rapidly They
Approach the Earth.

Those VIII have followed the work done
at the Lick Observatory within the last
few years recall the measurements Of We
. loCiti's made by Prof. ". W. Campbell
with the Mills spectroEraph From "a
study of the displacement of lines IN pho
. tographs of star spectra, IL has been pos
| SIIie 70 tell approximately how rapidly
celestial bodies were approaching or go
ing away rom the earth 1t Is only mo
ton in The line Of sight which is thus
diSceTnibIe. That which takes place at
right angles with this direction is known
as proper motion. and. If considerable.
can be asCertained uy noting Il stars
change Of apparent position teIescopiraIIy.
w hen star exhibits a double spectrum
and some of its lines are displaced to the
right, while others are shifted 10 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
phenomenon is observed. This is only a
l temporary situation though. since in a
true binary system. both bodies are NOV
/ ing about a common centre I'm circular
, or ellipticaI orbits.
In a bulletin recently issued by Prof
Campbell additional information is fur
nished in regard 10 Capella. whose double
character was announced from the Lick
Observatory two years ago. The two
members Of This pair seem 70 be naarly
equal in mass, proportions between en-
being as l26 is 10 l. The bigger one be
longs 10 the solar, or pale yellow, type
I Of star. while the smaller Is between the
solar and Sirian types. Sirius is a pure
white or BLUSH star. and some astrono-
mers believe that bodies Of this class are
hotter than the yellow stars. But upon
/ that point stellar SpectrosCOpists are not
now nearly 50 unanimous as they were
twenty years ago. Visually. the principal
star Of the pair is about one magnitude
| brighter than its companion. but photo
graphically they are more closely match
I ed.
The period required by the two compo-
nents Of Capella to traverse their orbits
/ has been found 10 be I04I days. ana a
rather abstruse calculation of the dis
/ taEce between them gives 100000 kilo-
meters or 54O00,C50 miles. II the smaller
/ body passed directly between the larger
one and the earth while making its revo-
tuition, there should be a trifiing Vet per-
ceptible diminUtiou Of Capclla light
every three and half months. But care
fui watch has failed to reveal any such
effect. 1t is therefore probable that the
orbit plane makes an appreciate angle
with the line of sight"
CaDella is by FAR the brightest OF the
spectroscopic binarics- Indeed. there is
only one star visible in the northern
I heavens which is distinctly more brilliant
Sirius. though Vega and Arcturus closely
/ rival II Capella now rises well up in
the northeast in time to be conspicuous
IN the late evening Aldebarau, being
redder, fainter and further south cannot
well be mistaken for il
The triple character OF POlaris. suspect
. ed FOR several months, is now formally
confirmed By Prof Campbell While lts
nature has been discovered by the spec
I troscOpe, tbs evidence A. different from
thtt by means Of which ''spectrOscopIc
/ olnafles are Identified There are not
ihree SeTarate spectra. whose lines are
Z shifted in different directions NJ intervals.
mere IS only one nght-emitting object
IT'D the grOuE- But inequalities in the
velocity with which this receGes from the
earth pointed to the fact that PoIaris
! mas dark companion. probably a moon
which rcNoives with II around com
mon centre
The period % this motion is 3 DAYS. %
/ hours and = minutes It was "a more
! complicated and "a slower task TO secure
proof that the pair is moving about an
"thrr comparatively distant centre. in
combination with a third BODY which is
/ also rOn-luminOus. The period of this
second movement Is not vet stated but
I Prof. 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. 1870 ia GroOmbridge's catalogue.
1 By Ball and others Il has been called the
/ runaway star It's proper motion
amounts 70 1l5 seconds of arc annually.
Coupling this fact with NeWcOrnb's eSti-
mate Of the distance OF CirOOmbridga. J SO
Prof Campbell gets $50 miles a second as
its velocity at right angles with the line
Of sight The director OF the Lick OBJ
scrvatOry has now. with the ala Of the
Mills spectograph. made q computation
Of the motion away from the earth and
4 This ne puts al ffty-eight or sixty miles
second.