Evening star., 1924-08-31
THE STARRY SKIES IN SEPTEMBER
By Prof. Barton of the University of Pennsylvania.

Mars still dominates the sky.
Although it was nearest and bright
est August %. it's distance has in
creased so little since then-600, 600
miles September THAT the planet is
still in very favorable position for
observation The position is mark ed
on figure l. To the naked eye the
planet looks like. red star of un-
usual brightness and unusual redness.
a little closer inspection shows that
it does not twinkle like the fixed
stars-Fromalhaut, for instance, at A,
southeast of Mars. Observations
made on different nights will reveal
its motion with respect to the stars
about it,
When we view Mars through a tele-
scope many factors determine what
can be seen. First of all. the planet
rotates upon its axis once in "a hours,
81 minutes. so that different parts of
the planet are successfully turned to-
ward the earth Its axis is inclined
about "a degrees to the plane Of the
obit in which it revolves about the
sun. and the plane of its orbit is
inclined a little less than degrees
TO that of the earth. For this reason
sometimes one of its poles is tipped
toward us and sometimes the other.
Then the planet has different phases.
only half of it being Illuminated by
the sun at one time. From the earth
we cannot see more than half of the
planet at one time. Often part of
the half we might see is not illumi
mated by the sun and it is not visible
The moon and the planets closer to
the sun than the earth have all the
phases, but planet whose orbit is
outside that of the earths can never
show crescent phase. The nearer
the planet is to the sun the greater
the departure from the full phase can
be. Figure shows the planet as it
appeared when nearest to the earth,
August %, and nearly as it appears
now. 1t is almost full AS it re-
cedes to the earth its apparent size
becomes smaller and smaller. and we
also see smaller part of the illumi-
mated half until December =, when
Mars shows the greatest departure
from the full phase. After that time
the disc appears smaller, but more
nearly fully Illuminated
Years on Mars Are Longer.
As the axis of rotation of Mars is
inclined to the plane of its orbit at
nearly the same angle as the axis of
the earth is inclined to the plane of
the earth's orbit there are seasons
'
earths but nearly twice as long. since
the year of Mars is 1.SS of our years
in length. The appearance OF Mars
changes with its seasons. Around
each of the poles of Mars a snow
white spot may be seen. The spot
forms as the Winter approaches at
each pole and gradually decreases in
size with the coming of Spring, and
sometimes disappears altogether.
Y h..r Nov 1, l. 81
is turned toward us. so that we can
see the changes at the south polar
cap better than those of the northern
This year the Winter of the Northern
Hemisphere of the planet--the Sum
mer of the Southern Hemisphere
begins October >, corresponding to
our December II. The season of Mars
on September l corresponds to ours
on November 80.
About half of the surface Ct Mars,
the northern half, is bright, and the
other half dark. 1t has been sup
posed that the lighter part is land
and the darker part water. but this
is found impossible. The lighter
parts are dull red and orange in color.
The darker parts vary from gray to
black. The surface features undergo
slight seasonal and other changes,
but are nearly permanent.
1t might be supposed that it is only
necessary to photograph the planet
in order to get a good representation
of its surface. This is not the case
for several reasons. There are many
difficulties. The planet rotates while
the exposure is being made. The red
color lengthens the exposure. The
image is very small and if enlarged
before photographing the exposure is
heightened and the small image can
not be enlarged indefinitely after ex-
poSure. Aside from the rotation, the
object to be photographed moves.
Just the stars twinkle. as seen
with the naked eye, so do they in a
telescope, and the motion is increased
in the same proportion that the tele-
scope magnifies. Every detail of the
planets disc is thus dancing. At some
moments all may be comparatively
quiet and the details seen sharply; in
the next moments the fine details may.
be lost by reason OF the agitation.
The eye can discriminate and look
only when the seeing is good. The
camera must take the good and bad
together, and the exposure is so long
that some bad is included. The only
thing to be done is to get a large
number of pictures and select the
best. Photographs are very valuable,
indeed, but the eye is still better for
this work.
We know very well a Photographic
plate will consistently show stars
with different comparative brightness
from that with which the eye sees
them, and different results will be OBJ
tanned with different kinds of plates.
We also know that there are some
who, having eyes, see not and others
who have visions. In the case of the
finest details on the surface of Mars
we are on the limit of vision. Some
have seen details which others have
not. This of itself is not surprising.
The details claimed are a series of