Butler citizen. [volume] (Butler, Pa.) 1877-1922, 1897-04-01
THE CITIZEN
APRIL ASTRONOMY.


Several typographical errors crept in !
to NV last article, which it is of consid- /
erable importance to have corrected. I,
For the angular diameter of Venus, in F,
stead of 81 minutes 6 seconds, read 31.6 T,
seconds of arc. For fumacs, read fur
naces: for septillous, read septillions; /
for aries. read Aries, and for Titan, read !
Titan
During the month of April all the
major planets except Uranus and Nep-
tune may be seen with the naked eye
between sunset and midnight Venus
although approaching the earth, is be-
coming less brilliant, because as she
overtakes the earth more and more of her
unilluminated disk is directed toward
the latter On the 2Sth she will be in
conjunction with the sun and nearest
the earth, the distance between the two
planets at closest approach being about
26I millions of miles. Venus sets this
evening at 9:31 and on the 18th at S:33,
local time
Mercury. on the 2Sth, will be at
greatest elongation from the sun, his
angular distance from the latter being
20 deg. and 43 seconds L. This planet
being somewhat elusive and difficult to
find, is seldom seen by ordinary observ-
ers, When in the best position for OBJ
servation he shines with the brilliancy
of an average star of the first magni-
tude. To those who wish to see Mer-
curry, we suggest the following easy
method of finding him. If the sky Is
clear ON the evening of the 2Sth, let the
observer at 7:55 o'clock, standard time
direct his eye to point in the horizon
20 degrees north of due west, and then
shift the gaze straight upward from
that point 10 degrees, and the object
sought for will be seen. These direc-
tions will be approximately correct for
two or three evenings before or after
the 28th, but the latter date is prefer
able if the meteorological conditions IA
vor it, as the planet is then at greater
elongation from the sun. At the time
indicated Mercury is equal in altitude
to the seven stars, and is only about a
degree south of that agglomeration.
1t will be interesting to observe the
large apparent size of the full moon ON
the 18th inst. The moon is in perigee
on that date, and is uncommonly close
to the earth A calculation shows that
the distance between the earth and its
satellite at P NJ on that day will be
but 222, 127 miles, center to center.
From surface to surface of the two
bodies would be but little more than
217, 600 miles, and if when the moon
crosses the meridian ON that date, it is
in the zenith of the observer (which 1t
will be in south latitude 20 degrees) he
may consider himself within that dis
tance of the lunar surface.
The question will naturally arise,
why is the moon so much closer to the
earth than usual at this time? Instead
of the earth being in one of the foc1 OF
the elliptical orbit which the moon de-
scribes. it is the common center of gra-
witty of these two bodies that is so sit
| uated, and both the earth and moon re-
volve around this common center OF
| gravity, the earth describing small
orbit of about 3, 900 miles radius. Now
when the earth is displaced from this
| common center of gravity towards the
moon and the moon is at the same time
at the lower apsis OF perigee, it follows
| that the moon must then be closer to
the earth than the average perigean dis
| tance by an amount equal to the radius
of the little orbit referred to. If when
the moon is at the lower apsis the earth
is displaced from the common center of
gravity in a direction from the moon, it
| is plain the distance between them will
be 5000 miles greater than the average
Iperigean distance. The distance of the
moon at apagee is likewise subject to
these variations, its maximum distance
being about 253, 900 miles.
| On the evening of April 5th an inter
esting phenomenon may be witnessed.
The two stars 10 Tauri and 20 Tauri of
the group the Pleiades will be oc-
Quilted by he moon. These stars are
very fain being each Of the 9Th magni-
tude, and good opera glass with per
fectly clear sky will be necessary to OBJ
serve the occultations, although it is
possible the immersions behind the
dark limb of the moon might be observ-
ed by extra good eyes unaided. When
not in proximity to the moon these stars
may be easily seen with the naked eye
The eastern standard time of the phases
and the angles of position as computed
for the latitude and meridian of Butler,
are as follows
| Immersion Elm ersion
| 10 Tauri 7:54 S:5S
20 Tauri S:17 Oil
| z Angles of position in degreea:-~
| Ar Immersion AT Emersion