Evening star., 1902-08-02
THE AU GUST SKIES
Jupiter is Seen Low in the
Southeast.
ST. ANDREWS SCROSS.
FORMED BY THE SIX BRIGHTEST
STARS IN THE SWAN.
How to Determine the Distances of
the Heavenly Bodies From Each
Other and the Earth.
Written for The Evening Star.

Written for The Evening Star.
Five stars of the first magnitude will be
above the horizon at o'clock this evening.
They are Vega. nearly overhead; Arcturus,
in the west; Spica, at a low altitude be-
tween west and southwest; Antares. a little
west of south. at one-fourth of the distance
from horizon to zenith Affair. at two-fifths
of the distance from Vega to the southeast
ern horizon
The very brilliant star seen low in the
southeast is the planet Jupiter. A short
distance to the right, or west OF Jupiter,
appearing as an orange-yellow star of the
first magnitude, is the planet Saturn.
Consultations.
Vega stands at one corner of the Lyre
Arcturus is in the left leg of Bo-otes, the
Herdsman. Between these two constella-
tions lie Hercules and the Northern Crown.
Between Hercules and the Pole Star is
Draco. the Dragon, the two eyes" of which
are nearly in line between Vega and the
Great Dipper. now in midheavens in the
northwest. At about the same altitude in
the northeast is the W-shaped figure Of
Cassiopeia. Below Vega, between it and
| the eastern horizon. is the Swan or North
ern Cross, and still lower between east and
northeast the great Square of Pegasus is
| fairly above the horizon. Antares stands
at the center Of the Scorpion. Affair marks
| the position of the Eagle; Between the
Eagle and the Square of Pegasus is the
sparking little constellation of the Dol
| phin. the Jobs Coffin" Of modern star
gaZers.
The Swan.
| This constellation is readily identified
from the arrangement of its six brighter
| stars in the form of a St Andrews cross.
| If the lowermost of these stars is omitted.
| the remaining five constitute a cross of the
| ordinary type; and, in fact, the consteEa~
tion, is known popularity as the Northern
| Cross The northernmost of these six stars
Alpha in the head of the Cross, tail of
| the Swan-is nearly up to the first magni-
| tude; the remaining five are rather below
| the second magnitude.
! The Swan, standing in the very thick of
| the Milky Way. occupies one of the richest
star regions in the heavens, and is a splen-
| did field for opera glass survey, particularly
the portion just north or the star Alpha. A
| large telescope brings its stars out In SEEM
| ingly inexhaustible profuson, affording one
| of the most impressive of celestial sights.
Are these stars, which shine so family that
| to the naked eye their existence is revealed
| only by their blended light. really enormous
| suns as they were assumed to be by Her.
schel. and as Is still held by most astrono-
mers to be the case, or may they not be
| comparatively Insignificant bodies. at no
| great distance from us, as star distances
go? This very interesting question IL at
| present unanswerable; the nature of the
Milky Way is still one Of the most profound
enigmas of the heavens.
Two Interesting Double Stars.
| The star Beta Cygni. which forms the foot
| of the Cross, the beak of the Swan, is one
of the most beautiful Of the colored double
| stars and is, moreover. wide enough to
be separable with ordinary spy glass. %
| 1t consists of an orange-yelow star of the
| third magnitude and a smaller companion,
| which is deep blue
A small circle on our chart marks the po-
| Sition Of a second double star, which, al
| though 1t shows no striking contrasts of
| color, it's components being both orange
| yellow and of about equal brilliancy, is still
| very pretty object even for a telescope
| which magniies no more than thirty or
| forty times. 1t Is of about the fifth mag
| nitude, and is, therefore, easily seen with
| the naked eye. Note its relation to the
| bright stars Of the Cross. and also that It
| is the uppermost of small triangle of stars
| of about equal brightness.
| This star is the famous 61 Cygni, inter-
esting as the first star to yield up to us the
secret Of its distance--or rather, the first
of which this discovery was announced, by
| Bessel some sixty years ago.
Measuring Star Distances.
The determining of star distance is a feat
of mensuration which may well be perplex-
ing to the unscientific reader. and few
| WOfQS III eluciOdtiOu U1 ttllS subject may De
| in order here. The method employed for
this purpose is based upon the familiar fact
that when we look at an object from two
| different points Of view we do not see it in
| the same direction from each point. In
consequence Of the earth's revolution in it's
orbit round the sun the point of view from
| which we see the stars is shifted semi-an-
| nually about 1856 0O00o0 mies-the diameter
| of the earth's orbit. Since the stars are
at unequal distances from us, some COM
paratiyely near and others vastly more re-
| mote there must be some shifting of their
| relative positions. as they are seen from
our changing points of view. Let us sup
pose for example. that two stars. one of
| which Is near. while the other is at a
observed on the LIST of January to be exact
4 ly in range with each other or, in other
| words, to be situated that a straight
| line run from the earth to the farther star
! passes through the nearer star. Clearly on
| the LIST OF July, when the earth has half
completed It's annual revolution. these two
| stars will no longer range exactly with
| each other The near star will be off the
| line, and the nearer 1t Is the greater vii!
/ be its shift Of position. The measurement
Of the amount of this shift in any given
case-this ''paraliax." as it is called-affords
| the astronomer, therefore, quantity by
means of which he can calculate the stars
distance. Some idea Qe the difficulty OF
making the requisite observations can be
| formed when Ii Is said that star has yet
been found to show a parallax as great as
one second Of angular measurement. This
| is the angle tnclosed between two straight