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Page 45
_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.
ASTEROIDS.
ALREADY DISCOVERED (1879), 192. DISTANCES FROM THE SUN, FROM 200,000,000
TO 315,000,000 MILES. DIAMETERS, FROM 20 TO 400 MILES. MASS OF ALL,
LESS THAN ONE-QUARTER OF THE EARTH.
The sense of infinite variety among the countless number of celestial
orbs has been growing rapidly upon us for half a century, and doubtless
will grow much more in half a century to come. Just as we paused
in the consideration of planets to consider meteors and comets,
at first thought so different, so must we now pause to consider a
ring of bodies, some of which are as small in comparison to Jupiter,
the next planet, as aerolites are compared to the earth.
In 1800 an association of astronomers, suspecting that a planet
might be found in the great distance between Mars and Jupiter,
divided the zodiac into twenty-four parts, and assigned one part to
each astronomer for a thorough search; but, before their organization
could commence work, Piazzi, an Italian astronomer of Palermo, [Page
163] found in Taurus a star behaving like a planet. In six weeks it
was lost in the rays of the sun. It was rediscovered on its
emergence, and named Ceres. In March, 1802, a second planet was
discovered by Olbers in the same gap between Mars and Jupiter, and
named Pallas. Here was an embarrassment of richness. Olbers
suggested that an original planet had exploded, and that more pieces
could be found. More were found, but the theory is exploded into
more pieces than a planet could possibly be. Up to 1879 one hundred
and ninety-two have been discovered, with a prospect of more.
Between 1871-75 forty-five were discovered, showing that they are
sought for with great skill. In the discovery of these bodies, our
American astronomers, Professors Watson and Peters, are without
peers.
Between Mars and Jupiter is a distance of some 339,000,000 miles.
Subtract 35,000,000 miles next to Mars and 50,000,000 miles next
to Jupiter, and there is left a zone 254,000,000 miles wide outside
of which the asteroids never wander. If any ever did, the attraction
of Mars or Jupiter may have prevented their return.
Since the orbits of Mars and Jupiter show no sign of being affected
by these bodies for a century past, it is probable that their number
is limited, or at least that their combined mass does not approximate
the size of a planet. Professor Newcomb estimates that if all that
are now discovered were put into one planet, it would not be over
four hundred miles in diameter; and if a thousand more should exist,
of the average size of those discovered since 1850, their addition
would not increase the diameter to more than five hundred miles.
[Page 164]
That all these bodies, which differ from each other in no respect
except in brilliancy, can be noted and fixed so as not to be mistaken
one for another, and instantly recognized though not seen for a
dozen years, is one of the highest exemplifications of the accuracy
of astronomical observation.
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