Evening star., 1924-06-29
THE STARRY SKIES IN JULY
By Prof. Barton of the University of Pennsylyania

The planets Jupiter and Saturn are
conspicuous objects In the southern
sky. Jupiter Is the brightest star
now visible in the early evening. Its
position Is marked on figure /, but
1t can be Identified at once by it's
brightness. The bright star near it
at A is Antares. The four brightest
satellites of Jupiter can be seen with
very small telescope. To follow
their motions from night to night Is
very interesting. Usually the four
satellites are visible, but sometimes
one or more may be directly between
us and the planet or directly behind
the planet, or In its shadow, and in
any OF these cases the satellite will
not be visible. July 26 will be an
especially seen. interesting 7.sa evening in this
ard time, satellite No. 2 comes be-
tween us and the planet and begins
transit over the face of the planet,
which lasts until 1853. At s:4s satel-
seen from the earth. This we cali an
occultation. This oceultation last un-
til the satellite emerges from the disc
OF Jupiter, but then it is In Jupiter's
illuminated; that is, it is eciipsed.
| The satellite reappears after the
eclipse at 1858 am. Satellite No.
| was occulted from SOL until 7:25. 1t
so its occultation is complete before
from s:Id until ntfa fi:ti Thus ffom follpsse sse
beginning Of the transit of No. 2 at
one of the four satellites, No. I. will
be in sight. That one is near It's
greatest distance to the west Of the
planet The shadow Of No. crosses
not often that three satellites are in
visible at the same time. 1t Is possi-
Bile for the four to be invisible at the
same time, but that occurs very
The cause of these phenomena is
shown approximately in figure 2.
This figure shows the orbits of the
three satellites. the shadow cast by
Jupiter in the direction opposite to
in direction to that of the earth
within which satellites cannot be seen
because Jupiter hides them, and the
the satellite is in the same direction
| as Jupiter, and, hence, cannot be seen
on the equally bright background of
Jupiter's disc. Too much space would
be taken to show the position of the
| fourth satellite.
Venus is now too close to the sun
to be seen. 1t passes the sun July l.
| and after that time is a morning star.
Al the emu Oh the NlOHln IL may De
seen in the east just before sunrise.
| The position of Saturn is marked on
| figure /. The bright star at B, near
Saturn, is Spica. The one above it, at
| c, is Arcturus. Mars is in the con-
stellation, Aquarius on the eastern
horizon. 1t rises about II o'clock.
! The position of Neptune is marked
near the western horizon, and is not
visible to the naked eye. Uranus,
also invisible to the naked eye, is in
| Pisces. while Mercury cannot be seen
point of its orbit farthest from the
| sun July 3.
A small partial eclipse of the sun.
| in which about fifth of the suns
| diameter is the greatest amount seen
eclipsed from any part of the earth,
| will occur on July 81. 1t will be seen
| only from regions near the south
pole, SO is of little Importance.
Mars, the planet next to the earth
| in order of distance from the sun,
which is closer to the earth than any
| other planet except Venus at times.
| will be almost as close to the earth
next month as it is possible for it to
| come 1t is now approaching the
| earth rapidly. Figure ) shows the
reason for this unusual condition
| Each planet moves around the sun in
| elliptical orbit. The earth's orbit is
nearly circular, with the sun a-little
out of the center. The variation in
the earth's' distance from the sun
amounts to 100000 miles. It is
closest in January, and. as stated
| The orbit of Mars. although more
| fattened than that OF any other planet
except Mercury, is nearly circular,
also with the sun a greater distance