Evening star., 1901-06-01
1 Il,

sion regarding the age of the Egyptian
pyramids.
To Watch the Shifting North Pole.
The shifting of the north pole Of the
heavens referred to above-the south pole
shifts in the same way-is due to the same
cause which effects the procession of the
equinoXes." explained last month, namely
a slow. gyratory motion of the earth as 1t
spins on its axis In consequence of this
motion the two points at which this axis
prolonged pierces the starry sphere are
movable, describing two circles in the
heavens, having "A radius of 231a degrees in
period of about 2J,S00 years. Besides
this professional movement the poles have
q minor movement, known as mutation
which is due to the fact that the earth is
loaded by the moon, and which has a
period of about nineteen years. The two
points at which the earth's- axis pierces
the heavens at any time are the celestial
poles for that time. 1t is desirable for
astronomers to know as exactly as posi-
bic where among the stars those points
Recently series of Photographic obser-
VationS has been commenced with this end
in view. the design being to continue them
for years and thus to obtain record dur
ing that time OF every change in the po-
sition of the north pole. The method en-
pioyed Is simply to point a photogra phic
telescope to the north celestial pole and
after night to take photographs of that
region with long exposure. AS the earth
turns on its axis, turning with it the teIe-
scope, and giving to the heavens the ap-
pearance of turning in the contrary direc-
ton, every star which casts it's image on
the Photographic plate will describe a
trail, forming an are of circle and
the common center of all of the ares will
or course, be the true pole during the time
that the plate was being exposed. The
telescope which is to do this work is
mounted at the observatory of Helsing-
fors In Finland, which offers the advantage
OF being In a high latitude. so that the
north pole is at a greater elevation above the
horizon and the troublesome effects of at
mospheric refraction are minimized The
plates are to be sent for measurement and
n. Y. which has special facilities for work
of this kind.
The Planets.
Mercury has been an evening star since
May IA, and by the first of this month
should become visible as such on a clear
evening. half hour or so after sunset, low
in the west. 1t will continue to be visible
as an evening star throughout the month
and we'll into July.
Venus has been an evening star since
April 80 and ought soon to be far enough
from the sun to become visible. On May
is Mercury and Venus were in corjunc-
tlon. The latter planet is, Therefore, now
the farther east and will be the first to be-
come visible. Mercury will continue to be
seen at higher altitude than Venus until
July /, when, in drawing in toward the
sun, it will again be in conjunction with
the brighter planet
Mars continues to be an interesting even
ing star. in the constellation Leo. Its posi-.
ton the first of the month is about ten
degrees east of Regulus During the month
1t will move about fifteen degrees farther
east.
Jupiter in Sagittarius. and Saturn, In the
same constellation, about twelve degrees
farther east, are both evening stars rising
at the beginning of the month shortly
after o'clock. BY the close of the
month they will both have become early
evening objects. in the southeast. Uranus
in the Scorpion, rises more than an hour
before Jupiter. 1t is some ten degrees
northeast of Antares. and is easily visible
through an opera glass.