The evening times., 1899-08-31
THB HDAVBNS IN AUTUMN
Bright Stars That Will Twinkle in
the Skies.
Summer VIII End at / $50 O'Clock In
the Afternoon of September 23.
How Mariners While at Sea COsn-
pute Latitude and LOngitude-The
Lunar Method of Finding Distances

Lunar Method of Finding Distances
During the month of September the
moons phases are as follows: New on the
4th, first quarter on the 18th, full on the
18th, last quarter on the Goth. She will be
in apogee on the I'd and Both, and in perigee
on the 18th. Even the most careful OBJ
server must have noticed that the moon
moves eastward among the stars every
night. performing revolution from star to
star in period of about 27 1-2 days, called
sidereal month. Since the suns eastward
motion among the stars is so much slower
than the moons, it is evident that the moon
from time to time overtakes and passes
the sun. The phases Of the moon depend
upon the relative position Of the earth,
moon, and sun. and the period from a new
moon to a new moon is called the synodic
month. which is nearly two and one-haif
days longer than the sidereal, and consti-
tutes the ordinary month. When the moon
is nearest to the earth, or in perigee, ii is
81. 900 miles nearer to the earth than when
she is remotest from the EARTH or in apogee
At the beginning Of the month Of Sep
tember the sun is little over degrees
distant from the equator, but will reach ii
on the 23d. at 80 o'clock in the afternoon,
at which moment the summer season Is at
an end and the autumn season begins.
In the almanacs the usual expression OF
this transition from the summer to the au-
tumn season is the sun enters Libra"
This is, however, not the constellation, but
the sign Libra. In consequence OF the pre-
cession of the eQuinoxes the signs and con-
stellations of the same name are no longer
identical, the consultations having, so to
speak. receded by one constellation behind
the signs of the same name. The division
of the zodiacal belt into twelve constella
tions is certainly a very convenient Cne,
but ii must not be supposed that the widths
OF these consultations are exactly the
same 1t would, in fact, be difficult mat
ter to define the line of demarcation. sepa-
rating one constellation from another, with
geometrical accuracy. The sun at the mo-
ment OF transition from the summer to the
autumn season will this year be in the
constellation of Leo, in stead of, as many
| might suppose, in that of Virgo, which is
the preceding constellation of Libra. but II
will enter Virgo the next day after the be-
ginning of the autumnal season. There
are, it is true, not few unsolved problems
in astronomy, but the determination Of the
exact position of the sun, moon, and the
planets at any day and hour of the year
does not belong to these, the astronomers
being able to fix these positions with such
accuracy as to elicit the amazement of all
persons that do not know the magical pow
er of mathematics and the nicely with
which astronomical observations are made
nowadays.
During the greater portion Of the month
Mercury will be in Leo, but about the 9th
will enter Virgo. Venus will he in Leo.
| too, at first very close to Regulus, the
| brightest star in that constellation. but
| toward the end of the month will enter
Virgo. At the time of the autumnal equi-
nox this planet will be near the sun.
Throughout the whole month it will not be
| favorable for observation with the naked
| eye. Mars is in Virgo. About the middle
of the month it will be near the bright
star Spica In that constellation. We may
| get a glimpse of this planet soon after
sunset when il will be lowering above the
| western horizon until about 7 O'Clock.
Jupiter is very near the boundary line of
Virgo and Libra, at first in the former,
and at the termination of the month within
| the latter constellation. The great planet
| will yet be acting as an evening star and
shine as such until nearly o'clock. Saturn
| is in Sagittarius, close to the boundary
| line of that constellation and Scorpio.
This planet will set a little before 10
o'clock in the evening.
1t is of course. plain to the reader that
the finding of the longitude and latitude
of places on the surface of the earth is of
the highest possible importance. and as
! it is distinctly an astronomical problem
| it is in place to say something about it in
articles devoted to astronomical subjects
There is a number of more or less simple,
ingenious and accurate methods OF both
finding the latitude and longitude. There
is not a ship crossing the sea on which
both OF these are not determined at least
once day, and this is done by means of a
| simple but indispensable instrument called
a sextant. 1t is astonishing what impor-
tant results can be obtained by means of
this simple and portable instrument. Sir
Jchn Herschei makes the noteworthy re-
mark about it, that a man with little
portable instrument held in his hand and
applied to his eye, even with so unstable
footing as the deck of a ship. shall say
positively within five miles where he is
OF boundless ocean. This, he adds, can
not but appear TO persons ignorant of phys
ical astronomy an approach to the millcu-
loas. And yet the alternatives of life and
death, wealth and ruin are daily and hourly
staked with perfect confidence on these
marvellous computations. One of the meth
ods employed at sea of finding the longi-
tude Of place is that by lunar distances.
In that guide so indispensable for the
| mariner-the Nautical Almanac-the dis
stars" from the moon are recorded for
every day IN tie year and for every three
hours each day for the sake of ships going
on long voyages and cruises, computed for
three years ahead. These nautical stars
are all situated near the moons path, and
their names are all familiar ones, viz, AL
pha, Arietis, Aldebaran, Pollux, Regulus.
Spiea, Antares, Affair, Fomalhaut, and
Markab, all of which, except the last, be-
long to zodiacal consultations, Markab. or
Alpha Pegasi, belonging to the constella-
ton Pegasus. The Nautical Almanac adds
| to these the distance of the moon from
the sun and the planets Venus, Mars, Ju-
piter, and Saturn. The distances laid down
in the almanac are computed as though
they had been observed from the centre of
the earth, but by mathematical process,
called clearing of the lunar" these al
manac distances can be reduced to those
observed at any place, and then the longi-
tude can be determined. OF course, the
usual method of finding the longitude at
sea is by means of the chronometer, but
voyages that the chronometer fails, and in
resorted to.
CygnuS, Caprfcornus, and DelphlnuS are
the three consultations which In this lati-
tude will come to the meridian about 8
o'clock in the September evenings. Cyg-
nus, or the Swan, is situated due east OF
Lyra and memorable for its shape-that of
conspicuous constellation is Alpha, of De-
Albireo, is at the foot The crosspiece is
lxod INV fhn fhra cto no1fo