Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1891-09-02
THE CELESTIAL SCENERY.
The. Heavens in Observation-Disclosures Of
Jupiter-The Harvest fMoon-Disappsar
ance of saturn's Ring-When to Look
nj uff

for Mercury-Fixed Stars Visible.
WRITTEN FOR THE DfsrATcH.l
Although there are no extraordinary
astronomical events on the calendar for
september, there will be many events that
viii be Of considerable interest to the stu
dent of astronomy, if not to the general
reader. The most Important events of the
month VIII be the opposition of Jupiter on
the 9th, the disappearance Of Saturn's ring
on the I'D and the arrival of the sun at the
autumnal equinox OF the 23d.
Jupiter is now in the constellation Aqua
RUS the Waterman, and is most brilliant ana
conspicuous of all the planets. On the even
ing of the 5th he rises at 6:25 at point loo
south of east. His angular diameter is 44.W
and viewed with telescope magnifying 40
! times would appear as large as the moon
does TO the unaided eye. Jupiter being on
that date at his shortest distance from the
earth, shines his brightest, and the present
month will be the most favorable time for
viewing his satellites, which may be seen
with an opera glass or small telescope. At
4:52 P. NJ. on the 9th, which is the exact time
Of opposition, Jupiter's position in right
ascension is 22h. Som. 4Ss. and his declination
is 50 L 5O'' south. His motion at present is
retrograde or westerly, and will continue TO
be so until November 3. after which 1t Will
be direct or easterly, and in the order of the
signs OF the zodiac. Jupiter and the moon
Will be in conjunction on the 18th at 1927 A.
NJ, the planet be ing 80 45' north OF the satel
lite.
The Harvest Moon.
The phenomenon commonly known as
the "harvest moon will be prominent
feature of Septembers celestial exhibition.
At the time of the full moon which occurs
nearest the autumnal equinox, the moon is
observed to rise but little later each even
ing, SO that the number of consecutive
moonlight evenings is greater than at other
seasons of the year.
The reason of this is that when the moon
is full in the autumn, it is always moving
northward, and is i'll that part of its orbit
which inclines least to the horizon, and
when it is full in that part of its orbit, it
rises less than half an hour later each even
ing, whereas the average daily retardation
is about 81 minutes. In the spring, when
the moon is moving sonthward at us iaii .h
horizon it rises about an hour and quarter
later each evening, and the number OF
consecutive moonlight evenings is less than
the average. 1t will be readily understood
that the nearer the moons orbit Is to being
parallel to the horizon, the less Is its
descent in moving given distance, ana the
successive days. So, conversely, the nearer
its orbit is to being perpendicular to the
horizon, the greater is the descent In mov-
ing given distance. SO that under rs such saar cir
sive risings of the moon would be greater
than usual. In high latitudes the phenome-
than in Pittsburg, while at the equator It is
entirely absent.
The Autumnal Equinox.
On the 23rd of the month, at 2:45 AM,
Pittsburg time, the sun reaches the half
way point between the solstices. At that
time if we ignore the effect of atmospheric
refraction, day and night are equal through
out the inhabited world. The effect of re-
fraction is to raise the sun about 35 from its
true place when in the horizon, thus in
creasing the length of the day, Or period of
sunlight, in q greater or less degree, accord
ing to the latitude. In the latitude of Pitts
burg it makes difference of but few min.
utes, but in latitude $50 the length of the
day, when the suns declinatior is zero, is
l3 Ii. S6 m, if we consider the day to include
the whole time during which any part of the
suns disk is above the horizon, SC that the
length OF the day is increased more than an
hour by refraction.
Practically, however, there is constant
day in that latitude at the time mentioned,
as the sun descends but 40 below the horf.
zon, so that there IS strong twilight all
night. In north and south latitude quo or ex-
actly at the poles, where there is a perfectly
parallel sphere, the sun at the time of the
equinoxes circles clear around the horizon,
touching successively every point OF the
compass. The sun when ut either equinox,
would rise due eastand set due west except
within few degrees OF the poles, were it
not for the effect of refraction before men
toned. As it is, such is really the case only
in the equatorial regions, but in moderate
that it does So while in very high latitudes
such an assertion would be altogether
wrong. Thus III north latitude $50 the set
ting amplitude of the SUMS upper limb, cor
rected for refraction, ON the 22nd of Septem-
Der is 12o from the west point toward the
north. The reason of this is that in very
high latitudes the apparent diurnal motion
is nearly parallel to the horizon, and the sun
or other heavenly body moves northward in
its diurnal course q considerable distance,
while descending the 35' which refraction
elevates it, so that the point at which the
grees north of where the real object sets.
saturn's Ring to Disappear.
An event of considerable interest marks
the end of September, and that is the disap-
pearance from view of the rings of Saturn
At that time the plane Of the rings, if con-
tinued, would pass through the center of the
earth, so it will be seen that only the edge of
the outer ring is presented TO view, which
through the most powerful .aeS telescope sap apt
extending for short distance on each side
of the planet. When only the edge of the
rings are turned toward the earth, Saturn
rings are opened so as to expose the nat side
to view. Saturn will, however, be entirely
invisible to the naked eye, till nearly the
close of the month"; on account of its prox-
unity to the sun, being in conjunction with
the sun on the 18th.
This is certainly not good month for
viewing the planets. Us only two OF them are
visible the majority of the time. In the
early part of the month Jupiter has the field
to himself as the only visible planet. Later
on Mars becomes discerniDle in the morning
sky, rising heliacally on the 18th. 1t is so
faint as to be very unattracttve, its appar- |
Ont diameter being only 3."9
Mercury will be visible during the last |
week of the month, but as it is then morn |
ing star, it will probably have few observers. |
1t is at its greatest elongation from the sun
on the 2Sth at P. M, and is then 17o So dis |
tant from the central luminary On the |
morning of the 2Sth it rises at ABB. which is |
exactly an hour and a half before sunrise |
the same morning ITS angular diameter at |
mated. 1t will at the time of visibility be in |
the constellation Leo and will appear fully |
as bright as an average star of the first mag
nitude. AS there are two bright stars close |
together, visible from the 2sth to the end of |
the month, it may be necessary to state that |
the brighter OF the two and the one the high |
er up is Mercury, the other one being Saturn,
which rises heliacally, or first becomes visi- |
the morning of the 18th, but they appear |
closer together each day and on the Both are |
only 80 apart. |
The Fixed Stars.
The fixed stars of the first magnitude |
visible in this latitude ut the present time |
are Vega, Arcturus, Antares, Altan and |
Fomalhaut, all of which may be seen any |
clear evening. Those visible in the morning |
are Capella Betelgeuse, Rigel, Aldebaran, |
PoIlux Sirius and Procyon. OF those visible |
in the early evening, Arcturus is the most |
brilliant, and it shines with ruddy glow in |
the western sky. On the evening of the 18th |
Sc OF u disfo nj OfI