The times. [volume] (Richmond, Va.) 1890-1903, 1898-01-09
THE SKIES IN JANUARY.
THE APPARENT MOTIONS OF THE
KING OF DAT.
The Pole Star-The Procession OF the
Equinoxes-Laplace's NebuIar Hy-
pothes latioDs.

On the 21st of December the sun reach
ed its scuthmost limit and from that
time 1t has been very slowly but contin-
ually moving northward again. The sun
has a twofoid motion when OF course Is
only apparent, for its apparent diurnaI
motion Is owing to the actual rotation OF
the earth on its axis and its apparent an
nual motion is due TO the revolution of the
earth about the sun in the plane of the
ccliptic, which is inclined to the plane
OF the equator at an angle OF . degrees
and q minutes, called the obliquity OF the
ecliptic. The latter undeTgoes a very
siynt but continuous change until 1t Will
reach its minimum, no less than l5,VO
years hence, when IL will be p degrees,
10 minutes. After having attained this
minimum il will begin TO increase again.
The fact that calculations can be made
involving such minute changes within
an enormous period of time furnishes u
splendid testimony to the wonderful pow
er OF mathematical analysis and the IN
genuity OF man in applying II to the
grandest science that has ever been de-
vissd by man. The motion of the earth
around the great luniinary, the sun, Is
not uniform, for it is performed not IN
a circle. but in an elongated curve, the
eclipse in one of the two fOci Of which
the sun is situated by whose attractive
power this motion IS generated. But
even if the earths motion in the plane
OF the eclptic were circular and uniform
the apparent motion of the sun north and
south OF the equator or 10 use technical
phrase in declination, would still be vari-
able, for meridans that divide the eclp-
tic into equal parts do not divide the
equator into such.
The reader not wholly unacquainted
with spherical geometry will readily I'M
derstand the reason for this. In conse-
quence of the unequal motion of the sun
in declination it will move at certain
times faster or more slowly than at 9TH
er times. Near the equator the sun
moves fast, whereas near the points of its
northernmost and southernmost limits IL
moves very slowly, nay at these limits
theselves it seems 20 stand still for a
time, for which reason these limits are
called solstices from the Latin meaning
| the standing still of the sun.
MOTION OF THE SUN.
The motion of the sun in declination
is of the highest importance, as the sea
sons of the year and the shifting of the
points of the suns rising and setting de-
pend upon it. In this oblique motion OF
the sun with reference to the equator. We
must also distinguish its motion in right
ascension from that in declinadon. the
former being along or rather parallel TO
the equator.
This motion is necessarily variable too.
| The angle which the diurnal paths of the
sun and the stars make with the horizon
| depends altogether upon the latitude Of
the place Of observation At the equa-
| tor for instance, the diurnal circles Of
ha nd CT ha qf
right angle. whereas at the poles they
move parallel to the horizon. which in
this case is the equator.
on all intermediate points the angle
is oblique, its magnitude depending upon
the latitude of the place. These three
| positions are respectively called the right
the parallel and the oblique spheres.
The latitude OF a place is always equal
TO the elevation Of She nearer pole above
the horizon, a fact Of the highest import
ance and worthy OF the earnest atten-
ton of the readers. By means Of an
| instrument, called the seXtant, the mani
| pulati0ng of which IS quite simple the
traveller can always with tolerable ac-
curacy determine the latitude of tie
place where he happens TO be by observ-
ing the angle of the pole star from the
horizon. In the southern hemisphere. the
in close enough proximity, this obser-
walton would be more difficult. IL IS
| necessary TO say here that the pole star
| does not exactly mark the true pole OF
the heavens around which the armament
makes one circuit every day. At present il
is about l degree II minutes distant from
the true pole. -Four thousand years ago
it was at a far greater distance from It.
IL we connect the brightest star in the
bowl of the little Dipper with the last
star but one in the handle of the large
Dipper by a straight line and bisect IL,
the point of dissection is marked by a
sufficiently bright star In the constellation
Draco called Thubari, which formerly
was the pole star. our present pole star
will approach the true pole of the heavy
ems within half n degree of II. This limit
will be reached in about n century. after
which IL will recede more ana more and
in about twelve thousand years our pole
star will no longer act in that capacity,
but yield that privilege to the brilliant
first magnitude star, Vega. This change Of
the position OF the pole of the heavens is
due TO what Is called the procession Of
the equinoXes n subject Of the highest
importance and interest, which We shall
explain as briefly as possible, as space
forbids us TO enter into a minute discus
sion OF IL. The points whore the eclptic
intersects the equator are called the YER
nal and autumnal equinoXes. These
points have been observed 10 move slowly
westward at the rate Of 50 degrees year.
The effect of this so-called procession,
misnomer since it is really recession,
is the change Of the pole OF the heay-
ems and a backing westward of the signs
Of the zodiac into the consultations west
of them Another effect is the difference
OF the tropical year from the sideresb
the former being 20 minutes shorter than
the latter, since 3G0 degrees are swept
through in about 36j IA days which makes
il - minutes for ~ seconds.
THE PHYSICAL CAUSE.
As to the physical cause OF the pre-
cession OF the equinOxes, we confine our
selves TO the remark that it arises from
the fact of the earth not being a sphere.
and of the tendency Of the plane Of the
Equator TO coincide with the plane OF the
ecliptic. in consequence of the attraction
OF the sun and moon upon the equatorial
ring. A full and entirely satisfactory
explanation would require more knowledge
OF analytical mechanics than we cam-in
fairness supposeu the general reader 10
possess The marvellous structure Of the
heavens I'm general. and OF the solar sys-
tenn in special cannot but arouse the ma
tional desire of knowing something OF It's
origin One OF the greatest mathema-
ticians the world has ever seen, the
Frenchman, Laplace, furnished theory
which, with some necessary notifications,
has been generally accepted as the most
probably true one. He supposed that
millions OF years ago Ian accurate state
ment in this respect lies beyond the limits