Evening star., 1924-09-28
THE STARRY SKIES IN OCTOBER
By Prof. Barton of the University of Pennsylvania

Mars, which has been discussed so
| much in recent months, is still the
| most conspicuous object in the sky,
although it is less than half as bright
brightness will still further decrease
| a whole magnitude during the month,
so that by the end of the month 1t
will be only forr-tenths as bright as
| at the beginning. The decrease in
| brightness is due principally.to Its in
crease Of distance from the earth.
When nearest in August it was 34,-
100000 miles away. 1t is now a.
| 900, ,0G0 miles away, and at the end of
the month 61.000.00 miles. On Sep
tember "a it ceased its westward, or
retrograde motion, and is now NOV
| ing eastward slowly. The position
! at the first and last Of the month are
shown on figure 1. 1t will move more
| rapidly in the coming months, twice
as far next month. This motion and
| the decrease in brightness will be in
teresting to follow.
Just above Mars, at A. Is the group
of stars in Aquarius. which form
group known as the Y in Aquarius,
since they are arranged roughly in
| the form of that letter. They are the
| water jar which Aquarius tthe water
| carrier) carries. Southeast of Mars,
at B. is the bright star Fomalhaut,
| which is farther south than any other
first magnitude star seen here.
Canals on Marss
The south polar cap Of Mars is now
| turned toward us. The Summer on
| the southern hemisphere of Mars be-
gins October 5. The polar cap is now
melting-perhaps we should merely
say decreasing in size-for it is hard
| to believe that the temperature is
l r.
| They can disappear by evaporation.
Those who maintain that the canals
really exist say that they are for the
purpose of carrying the water from
the melting ice cap into the desert
regions. All admit that water Is very
scarce on the planet. AS the water
| flows along the canals. the vegetation
| along its banks thrives, and it is the
strip of vegetation rather than the
| canal that We see. From the rate at
which the darkening proceeds the
rate of the fiow of the water has been
found to be 2.1 miles per hour. The
| canals are more conspicuous after the
polar cap has melted-that is, now,
during the Summer season. Hence
| the canals were not expected to be
| conspicuous when the planet was
| nearest. 1t was not the proper sea-
son. However, not merely these de-
|
canals themselves has been grave1y
| doubted
| Mars is one of the smallest OF heav-
| emily bodies. 1t has diameter of
only 4,20O miles. This compares with
1920 miles diameter for the earth,
1900 for Venus. 1900 for Mercury and
2,16O for the moon. These relative
| sizes are shown in figure >. Mars has
very nearly twice the diameter of the
| moon. Mercury alone OF the ma jor
planets is smaller. but small as is the
| planet it has two satellites or moons
| revolving about it. These satellites
are exceptional in several ways. Mars
| is the smallest body observed to have
| another revolving about 1t. These
satellites are the smallest in the solar
system. They are so small that their
diameters cannot be accurately deter
mined. One estimate of their diam
eters is 36 miles for the inner one
| and 10 for the outer one. The inner
one is the brighter, but harder to OBJ
! serve, because of the glare of the
planet. They are among the most
difficult objects to observe by reason
of their faintness and the glare of the
planet. The inner satellite Phobos is
| only $3.50 miles from the surface of
the planet, and is SO close as to be in
visible from a considerable portion of
! the surface Of Mars. No other Satel-
| lite is so close to the body about
| which it revolves.
Revolutions Of the Planets.
| Phobos revolves about the planet Z
| hours and 80 minutes, while the
planet requires "a hours and 81 min
utes to turn on it's axis. This condi-
! tion is also unique in the solar sys-
| TEN. No other satellite revolves in a
| period less than that of the rotation
l Ioft ~ r. IL -; l. t.
| The revolution of the satellite re-
| Quires just a trif1e under third as
| long as the rotation Of the planet. A
| similar condition with our moon
would mean that the moon, instead of
! revolving about the earth in a month