Evening star. [volume] (Washington, D.C.) 1854-1972, 1897-07-03

III IlluneaVenS IN the
northwest, and overhead the Dragon, Her.
cules, Bootes and the Northern Crown
The Swan (Cygnus) is easily identified
from the arrangement of its six brighter
stars in the form of "a St. Andrews cross.
The northernmost Of these stars, Alpha
Cygni, known also as Deneb, the Tail" is
of above the average. of second-magnitude
brightness and is Sometimes reckoned
among the first-magpitude, stars The re-
naming five are, nohceably less brilliant,
being barely above the third magnitude
Deneb, as Its name implies is in the
Swans tail; the head is emarked by the
star Beta on the extreme right. This star
also marks the foot of the Gross The
arms of the Cross form the Swans wings.
The Swan lies in the thick of the Milky
Way and is one of the richest of the con-
stellations in stars visible or invisible to
the naked eye.
Alpha Cygni is one of the ten brilliant
stars Of the northern hemisphere upon
which DR.. Elkin few years ago made a
series of observations with the Yale Col
lege hellometer for the purpose of ascer-
tanning their distances from us and # is
one of these-Arcturus being another-of
which the 'parallax" proved to be a uuan-
tity SO minute that no trustworthy meas
urement of 1t could be obtained. Bright as
this star is, it is apparently plunged in
space to depth unfathomable by anv
means now available to astronomers, and
we must regard it of those stu
pendous suns by the side Of which our own
brilliant luminary would become a mere
pigmy.
The star Beta is a beautiful colored
double star. sufficiently wide to be sep
arated by even a small telescope. Its com
ponents are yellow and deep blue 1t is
the most splendid object of its class in the
entire heavens.
An Interesting Star.
A small circle on the planisphere marks
the position of a star, which, though of
only the fifth magnitude, is far more in
terestlnS than either of the stars Just men
toned, I'll Cygni, famous the first of the
stars to surrender the secret of its dis
lance, or, rather, the first of which this
discovery was announced, by Bessel some
sixty years ago. The star is visible to the
naked eye, and can easily be found from
its position at one corner of a four-sded
figure, of which the three other corners
are marked by the three lower stars of the
cross. A little triangle of stars, brought
out very prettily with an opera glass. will
be found here. The star in question is the
uppermost of the three which form this
triangle; A telescope which magnities no
more than twenty or thirty times will
show 1t to be double star its components
being OF about the same -brilliancy and
both of deep orange color.
star distances are determined nv meas
urlng the amount of change which takes
place In the position of a star with refer
ence to it's neighbors in consequence of the
change in our point of view, in the course
OF the year, due to the revolution of the
earth in its orbit around the SUM- The
diameter of the earth's orbit is about 1s5.-
UO,OOO miles. In the course of the six
months required by the earth to go half
way around this immense circle our posi-
ton In space changes, of course, to this
extent. Suppose that at the beginning of
the SIX months two stars. one of which is
comparatively near us, while the other Is
almost infinitely remote, are seen to be
very nearly in range with each other Then
at the end of the six months the range will
not be precisely the same; the two stars
will appear a little closer together or a lit
tie farther apart, as she case may be, the
nearer star having rHbved.apparently, and
the nearer to us It IS theit greater will be
the amount Of !, this shiftI.of position. or
quantity which the astronomer aiming to
find the stars distance must measure. To
give some idea of the difficulties involved
in the measurement it may be said that no
star has yet been found of which the paral-
lax or annual shift Of position is large
as one second of angular measurement.
One second Is the angle included between
two straight lines which, starting at a
common point, diverge SO slowly that at a
distance of three and quarter miles they
are but one inch apart. In order that they
radius OF the earth's orbit-for it can be
shown eeometrically hat the "parallaX" Ct
star is the angle which would be SUBJ
tended by the earth,s orbit, viewed from
the distance of the star-these lines must
have a length of about twenty million mil
lion miles. This would therefore be the dis
lance of the star of which the parallax
was one second. That of 81 Cygni is less
than half second, and its distance ac-
cordingly is more than forty million million
miles. or, in round numbers, 100000 times
the distance of the sun-a distance travers-
Cd by light in about seven years.
Immensc Distances.
A stars distance being known. some idea
may be formed of It's size from the bril-
liancy of its light. It has been estimated
that the combined masses Of the two bodies
which form the star 81 -Cygni would make
single sun about half as massive as ours.
which in their place would shine as star
OF the third magnitude. The most striking
tact In this case, however, is that although
these two bodies appear to the naked eye,
ana even when looked at through Q field