The times. [volume] (Richmond, Va.) 1890-1903, 1898-10-23
HOW FAR AWAY ?
\ New Method 10 Determine the Dis
lance of "a star.


Among the capabilities Of the spectro-
scope Is its power Of Indicating the
rapidly OF n stars movement "In line
OF sight" that Is, directly toward us or
directly from us. Such a movement is
shown by slight. yet measurable. dis
placement OF the lines OF the stars spec
trum. to the right or the left as the case
may BE-. the amount OF which displace-
ment is proportiOned to he rate Of the
stars movement.
A very ingenious use has lately been
made Of this fact for determining the
distances from US Of some OF the binary
stars.
a binary .star-Or 10 speak more
strictly a binary system--conssts of two
stars or suns. which are revolving one
about the other Ike two balls OF a
dumbbell tossed into the air. Il the orbit
IN which they circle IS set more or less
edgewise toward US. then one star will be
approaching while the other is seceding-
except when. as they pursue their circu-
lar course both are moving sqcprely
across the line OF sight-and this differ
ence Of movement can be detected with
the spectrOscOpe
one OF the largest known II these
binary stars-discOyered 10 be bina-y by
the elder Herschel-is Gamma Virgins,
Il star OF the third magnitude. not far
from the bright star Spica, In the con-
stellation Virgo. Professor BelopOlsky.
OF the PulkOWa Observatory. has re-
Gently made a spectroscopic study OF this
star for the purpose OF determining lis
distance by the method ,5oye indicated.
and here are the results If lis Obsera-
tons
One Of the two components " Gamma
Frs.r
rs at the rate OF 1349 miles a second;
the other. at the rate Of l2sl miles a
second. The difference in these two
ates, LIS miles a second. must be due
TO the orbital movement OF one star
about the other. or more strictly. Cf both
about their common centre OF gravity.
These figures form the basis Of the pro-
fessor's calculations. The orbit of the
companion Of Gamma Virgins. he u rger
star being regarded as stationary-has
been calculated and plotted by several
astronomers. Knowing, then. the lay OF
this orbit in space. he could determine
easily from the stars observed rate OF
recession how fast 1t actually travels In
its orbit. a part OF its movement Delhs
lcross the line Of light.
Now. It is known that this companion
star reyOlves around its primary In
period OF $50 years. The rate In miles
Der second at which 1t travels having
been found, the size OF the orbit could
be figured out easily. DR.. BeOpolsky
found that its size is such that. one-half
0f its longer diameter is 1914 times the
oarth's distance from the sun, or more
than two and a half times that OF Nep-
tune from the sun.
The farther away a thing Is the smaller
it looks 10 be. Having discovered the
actual size of this orbit, and knowing
how small II appears 10 be-or. what
amounts 10 the same thing, knowing the
apparent distance apart OF the two stars
which form Gamma Virginis-the as
trOnomer was able next 10 determine how
Tar away the system Is He found Its
distance from us TO be so great that light
requires 81 years 10 flash across the IN
tsryening space. The sun removed 10
that distance would become a star or the
sixth magnituds-one OF those little
twinklers just visible to the naked eye.
The combined mass of the two suns which |
form Gamma Virgins, according TO Be
lopolsky's calculations. is about ID times
that OF the sun.
Another very interesting binary star I
IS Gamma Leons. the third star in the |
sickle" reckoned from Regulus. IL Is
OF about the same magnitude as Gamma /
Virgins. and, like that star. II is a very !
pretty object for a small telescope. Pro-
lessor Belopolsky finds that the SEMI
ionger-of the orbit IN this
case is l02 times that of the earth's orbit |
that the combined mass OF the TWO stars /
which form the binary Is 90 times tne
SUMS mass and that the distance OK the
system from US Is l61 light years
The principle which underlies this METH ,
od-iirst 10 determine the actual size or +
the orbit in the case OF binary ana
then 10 determine its distance from us
apparent size-is simple enough. Tns
difficulty In applying the principle lies
in the minuteness Of the quantities which