The god or war; Its sign [Symbol], spear and shield.
MEAN DISTANCE FROM THE SUN, 141,000,000 MILES. DIAMETER, 4211 MILES.
REVOLUTION, AXIAL, 24H. 37M. 22.7S.; ORBITAL, 686.98 DAYS. VELOCITY
PER MINUTE, 899 MILES. SATELLITES, TWO.
[Illustration: Fig. 62.--Apparent Size of Mars at Mean and Extreme
Distances.]
At intervals, on an average of two years one month and nineteen
days, we find rising, as the sun goes down, the reddest star in
the heavens. Its brightness is exceedingly variable; sometimes
it scintillates, and sometimes it shines with a steady light. Its
marked peculiarities demand a close study. We find it to be Mars,
the fiery god of war. Its orbit is far from circular. At perihelion
it is 128,000,000 miles from the sun, and at aphelion 154,000,000;
hence its mean distance is about 141,000,000. So great a change
in its distance from the sun easily accounts for the change in
its brilliancy. Now, if Mars and the earth revolved in circular
orbits, the one 141,000,000 miles from the sun, and the other
92,000,000, they would approach at conjunction within 49,000,000
miles of each other, and at opposition be 233,000,000 miles apart.
But Mars at perihelion may be only 128,000,000 miles from the sun,
and earth at [Page 160] aphelion may be 94,000,000 miles from the
sun. They are, then, but 34,000,000 miles apart. This favorable
opportunity occurs about once in seventy-nine years. At its last
occurrence, in 1877, Mars introduced to us his two satellites, that
had never before been seen by man. In consequence of this greatly
varying distance, the apparent size of Mars differs very much (Fig.
62). Take a favorable time when the planet is near, also as near
overhead as it ever comes, so as to have as little atmosphere as
possible to penetrate, and study the planet. The first thing that
strikes the observer is a dazzling spot of white near the pole which
happens to be toward him, or at both poles when the planet is so
situated that they can be seen. When the north pole is turned toward
the sun the size of the spot sensibly diminishes, and the spot at
the south pole enlarges, and _vice versa_. Clearly they are
ice-fields. Hence Mars has water, and air to carry it, and heat to
melt ice. It is winter at the south pole when Mars is farthest from
the sun; therefore the ice-fields are larger than at the north pole.
It is summer at the south pole when Mars is nearest the sun. Hence
its ice-fields grow smaller [Page 161] than those of the north pole
in its summer. This carrying of water from pole to pole, and melting
of ice over such large areas, might give rise to uncomfortable
currents in ocean and air; but very likely an inhabitant of earth
might be transported to the surface of Mars, and be no more
surprised at what he observed there than if he went to some point of
the earth to him unknown. Day and night would be nearly of the same
length; winter would linger longer in the lap of spring; summer
would be one hundred and eighty-one days long; but as the seas are
more intermingled with the land, and the divisions of land have less
of continental magnitude, it may be conjectured that Mars might be a
comfortable place of residence to beings like men. Perhaps the
greatest surprise to the earthly visitor would be to find himself
weighing only four-tenths as much as usual, able to leap twice as
high, and lift considerable bowlders.
_Satellites of Mars._
The night of August 11th, 1877, is famous in modern astronomy.
Mars has been a special object of study in all ages; but on that
evening Professor Hall, of Washington, discovered a satellite of
Mars. On the 16th it was seen again, and its orbital motion followed.
On the following night it was hidden behind the body of the planet
when the observation began, but at the calculated time--at four
o'clock in the morning--it emerged, and established its character as
a true moon, and not a fixed star or asteroid. Blessings, however,
never come singly, for another object soon emerged which proved
to be an inner satellite. This is extraordinarily near [Page 162]
the planet--only four thousand miles from the surface--and its
revolution is exceedingly rapid. The shortest period hitherto known
is that of the inner satellite of Saturn, 22h. 37m. The inner
satellite of Mars makes its revolution in 7h. 39m.--a rapidity so
much surpassing the axial revolution of the planet itself, that it
rises in the west and sets in the east, showing all phases of our
moon in one night. The outer satellite is 12,579 miles from Mars,
and makes its revolution in 30h. 18m. Its diameter is six and a
quarter miles; that of the inner one is seven and a half miles. This
can be estimated only by the amount of light given.