The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1890-12-19
ASTRONOMICAL EVENTS IN 1891.
Transit OF Mercury on May 9--Total
Eclipse of the Moon.

Rochester Democrat.
The most interesting astronomical event
OF the coming year will be the transit of
Mercury on the 9th of May. In this longi-
tude the transit will begin a half hour be-
fore sunset, and the conditions viii be very
unfavorable for observation, except of the
entrance of the planet upon the suns disk.
A journey to Denver, Colo, will be neces-
sary to secure fair observations. 1t is prob
able that some organized effort will be
made to observe the transit.
During the year 1891 there will be two
partial eclipses of the sun. The first
eclipse of the sun will take place on the
9th of June In Siberia the eclipse viii be
annular. In the northwestern portion of
the United States the sun will be partially
obscured Detroit is the nearest point
from which any part of the eclipse viii be
visible. On the 1st of December there will
be partial eclipse of the sun visible in the
southern part of South America.
November Is there viii be total eclipse
of the moon visible here. 1t will begin
here about 8 80 o'clock in the evening, or
a short time after the moon rises. This
win be an event of considerable interest.
A total eclipse of the moon on the ed of
May viii be visible in Europe.
Astronomers have recently adopted an
ingenious method for determining the
position of the pole OF the heavens, or
rather the point where the earth's axis
prolonged would be located in reference to
the nxed stars. The pole star is short
! distance from the pole, and a true north
and south line on the earth is determined
by sighting across two objects
or through transit instrument at the
pole star when it appears to be directly
above or below the true pole. Astrono-
Iners will direct Photographic instruments
at the pole star, and by long exposure al
low the star to describe circle or portion
OF a circle on the sensitive plate. The CEN
ter of this circle will be the
true pole for the date of the ex-
posture. 1t is expected that the movement
of the pole caused by the wabbling of the
earth from the moons attraction will be
determined by series of photographs
The results of such investigation may
prove to be very interesting. Much, how
ever, Will depend upon the stability OF the
Photographic instrument.
ANY one who has 4 camera can try the
experiment by aiming the instrument at a
| bright star to get the focus. and then put
ting the camera in sheltered place and
pointing it at the pole star. The camera
must be sheltered from the electric light or
| reflected moonlight. An exposure of four
or i've hours would give the circular marks
of great number of circumpoIar stars. If
the camera lens be of wide angle and short
locus, IL would propdbiy take IN the little
dipper. Some of our amateur photogra-
pliers should try this experiment and CON-
pare notes. The arcs made by the stars
might be sufficiently accurate for a rough
determination of the place Of the true pole.
If the camera were used for several nights,
the central points as determined from
the ares should coincide if the pole has
not changed position. If the lines
or ares made by the star images are
| thin enough, the central point may be
found by the we'll known geometrical
formula for determining the center of q
circle which shall pass through three points
| not in q straight line. That is, take three
| points in the arc made by that star and
draw two chords. one between the first
| and second points and another between
the second and third points. Bisect each
chord and erect perpendicular from the
points of dissection. If the work be care
| fully done the point where the
perpendlculars meet will be the
center of the circle. The center may also
be found by trial with a pair of dividers.
The experiment will certainly be very in
teresting, and it may be possible for some
OF cur amateur photographers and students
OF geometry to ascertain if the earth wab-
bles to such an extent as to be ascertained
by an ordinary camera