Recreations in Astronomy by Henry Warren

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How terrible is the fear of ignorance and superstition when the sun
or moon appear to be in the process of destruction! how delightful
are the joys of knowledge when its prophesies in regard to the
heavenly bodies are being fulfilled!

MARS.

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.

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.

JUPITER.

The king of the gods; sign [Symbol], the bird of Jove.

DISTANCE FROM THE SUN, PERIHELION, 457,000,000 MILES; APHELION,
503,000,000 MILES. DIAMETER, EQUATORIAL, 87,500 MILES; POLAR, 82,500
MILES. VOLUME, 1300 EARTHS. MASS, 213 EARTHS. AXIAL REVOLUTION, 9H.
55M 20S. ORBITAL REVOLUTION, 11 YEARS 317 DAYS. VELOCITY, 483.6
MILES PER MINUTE.

[Illustration: Fig. 63.--Jupiter as seen by the great Washington
Telescope. Drawn by Mr. Holden.]

Jupiter rightly wears the name of the "giant planet." His orbit
is more nearly circular than most smaller planets. He could not
turn short corners with facility. We know little of his surface.
His spots and belts are [Page 165] changeable as clouds, which they
probably are. Some spots may be slightly self-luminous, but not the
part of the planet we see. It is covered with an enormous depth of
atmosphere. Since the markings in the belts move about one hundred
miles a day, the Jovian tempests are probably not violent. It is,
however, a singular and unaccountable fact, as remarked by Arago,
that its trade-winds move in an opposite direction from ours.
Jupiter receives only one twenty-seventh as much light and heat from
the sun as the earth receives. Its lighter density, being about that
of water, indicates that it still has internal heat of its own.
Indeed, it is likely that this planet has not yet cooled so as to
have any solid crust, and if its dense vapors could be deposited on
the surface, its appearance might be more suggestive of the sun than
of the earth.

_Satellites of Jupiter._

In one respect Jupiter seems like a minor sun--he is royally attended
by a group of planets: we call them moons. This system is a favorite
object of study to everyone possessing a telescope. Indeed, I have
known a man who could see these moons with the naked eye, and give
their various positions without mistake. Galileo first revealed
them to ordinary men. We see their orbits so nearly on the edge
that the moons seem to be sliding back and forth across and behind
the disk, and to varying distances on either side. Fig. 64 is the
representation of their appearance at successive observations in
November, 1878. Their motion is so swift, and the means of comparison
by one another and the planet so excellent, that they can be seen
to change their places, [Page 166] be occulted, emerge from shadow,
and eclipse the planet, in an hour's watching.

[Illustration: Fig. 64.--_a._ Various Positions of Jupiter's Moons;
_b._ Greatest Elongation of each Satellite.]

ELEMENTS OF JUPITER'S SATELLITES.
+-------------------------------------------------------------+
| | Mean Distance | | |
| | from Jupiter. | Sidereal Period. | Diameter.|
| |---------------+------------------+----------|
| | Miles. | Days Hrs. Min. | Miles. |
| I. Io | 260,000 | 1 18 28 | 2,352 |
| II. Europa | 414,000 | 3 13 43 | 2,099 |
| III. Ganymede | 661,000 | 7 3 59 | 3,436 |
| IV. Callisto | 1,162,000 | 16 18 5 | 2,929 |
+-------------------------------------------------------------+

It is seen by the above table that all these moons are larger than
ours, one larger than Mercury, and the asteroids are hardly large
enough to make respectable moons for them. They differ in color:
I. and II. have a bluish tinge; III. a yellow; and IV. is red.
The amount of light given by these satellites varies in the most
sudden and inexplicable manner. Perhaps it may be owing to the
different distributions of land and water on them. The mass of all
of them is .000171 of Jupiter.

[Page 167]
If the Jovian system were the only one in existence, it would be
a surprising object of wonder and study. A monster planet, 85,000
miles in diameter, hung on nothing, revolving its equatorial surface
forty-five miles a minute, holding four other worlds in steady
orbits, some of them at a speed of seven hundred miles a minute,
and the whole system carried through space at five hundred miles
a minute. Yet the discovery of all this display of power, skill,
and stability is only reading the easiest syllables of the vast
literature of wisdom and power.

SATURN.

The god or time; sign [Symbol], his scythe.

MEAN DISTANCE FROM THE SUN, 881,000,000 MILES. DIAMETER, POLAR,
66,500 MILES; EQUATORIAL, 73,300 MILES. AXIAL REVOLUTION, 10H.
14M. PERIODIC TIME, 29T YEARS. MOONS, EIGHT.

The human mind has used Saturn and the two known planets beyond
for the last 200 years as a gymnasium. It has exercised itself
in comprehending their enormous distances in order to clear those
greater spaces, to where the stars are set; it has exercised its
ingenuity at interpreting appearances which signify something other
than they seem, in order that it may no longer be deluded by any
sunrises into a belief that the heavenly dome goes round the earth.
That a wandering point of light should develop into such amazing
grandeurs under the telescope, is as unexpected as that every tiny
seed should show peculiar markings and colors under the microscope.

[Illustration: Fig. 65.--View of Saturn and his Rings.]

There are certain things that are easy to determine, such as size,
density, periodic time, velocity, etc.; but other things are exceedingly
difficult to determine. It requires long sight to read when the
book is held [Page 168] 800,000,000 miles away. Only very few, if
more than two, opportunities have been found to determine the time
of Saturn's rotation. On the evening of December 7th, 1870,
Professor Hall observed a brilliant white spot suddenly show itself
on the body of this planet. It was as if an eruption of white hot
matter burst up from the interior. It spread eastward, and remained
bright till January, when it faded. No such opportunity for getting
a basis on which to found a calculation of the time of the rotation
of Saturn has occurred since Sir William Herschel's observations;
and, very singularly, the two times deduced wonderfully
coincide--that of Herschel being 10h. 16m., that of Mr. Hall being
10h. 14m.

[Page 169]
The density of Saturn is less than that of water, and its velocity
of rotation so great that centrifugal force antagonizes gravitation
to such an extent that bodies weigh on it about the same as on the
earth. All the fine fancies of the habitability of this vaporous
world, all the calculations of the number of people that could
live on the square miles of the planet and its enormous rings,
are only fancy. Nothing could live there with more brains than a
fish, at most. It is a world in formative processes. We cannot hear
the voice of the Creator there, but we can see matter responsive
to the voice, and moulded by his word.

_Rings of Saturn._

The eye and mind of man have worked out a problem of marvellous
difficulty in finding a true solution of the strange appearance
of the rings. Galileo has the immortal honor of first having seen
something peculiar about this planet. He wrote to the Duke of Tuscany,
"When I view Saturn it seems _tricorps_. The central body seems the
largest. The two others, situated, the one on the east, and the
other on the west, seem to touch it. They are like two supporters,
who help old Saturn on his way, and always remain at his side."
Looking a few years later, the rings having turned from view, he
said, "It is possible that some demon mocked me;" and he refused
to look any more.

Huyghens, in March, 1655, solved the problem of the triform appearance
of Saturn. He saw them as handles on the two sides. In a year they
had disappeared, and the planet was as round as it seemed to Galileo
in 1612. He did not, however, despair; and in October, [Page 170]
1656, he was rewarded by seeing them appear again. He wrote of
Saturn, "It is girdled by a thin plain ring, nowhere touching,
inclined to the ecliptic."

Since that time discoveries have succeeded one another rapidly.
"We have seen by degrees a ring evolved out of a triform planet,
and the great division of the ring and the irregularities on it
brought to light. Enceladus, and coy Mimas, faintest of twinklers,
are caught by Herschel's giant mirrors. And he, too, first of men,
realizes the wonderful tenuity of the ring, along which he saw
those satellites travelling like pearls strung on a silver thread.
Then Bond comes on the field, and furnishes evidence to show that
we must multiply the number of separate rings we know not how many
fold. And here we reach the golden age of Saturnian discovery,
when Bond, with the giant refractor of Cambridge, and Dawes, with
his 6-1/3-inch Munich glass, first beheld that wonderful dark
semi-transparent ring, which still remains one of the wonders of
our system. But the end is not yet: on the southern surface of
the ring, ere summer fades into autumn, Otto Struve in turn comes
upon the field, detects, as Dawes had previously done, a division
even in the dark ring, and measures it, while it is invisible to
Lassell's mirror--a proof, if one were needed, of the enormous
superiority possessed by refractors in such inquiries. Then we
approach 1861, when the ring plane again passes through the earth,
and Struve and Wray observe curious nebulous appearances."[*]

[Footnote *: Lockyer.]

Our opportunities for seeing Saturn vary greatly. As the earth at
one part of its orbit presents its south pole [Page 171] to the sun,
then its equator, then the north pole, so Saturn; and we, in the
direction of the sun, see the south side of the rings inclined at an
angle of 27 deg.; next the edge of the rings, like a fine thread of
light; then the north side at a similar inclination. On February
7th, 1878, Saturn was between Aquarius and Pisces, with the edge of
the ring to the sun. In 1885, the planet being in Taurus, the south
side of the rings will be seen at the greatest advantage. From 1881
till 1885 all circumstances will combine to give most favorable
studies of Saturn. Meanwhile study the picture of it. The outer ring
is narrow, dark, showing hints of another division, sometimes more
evident than at others, as if it were in a state of flux. The inner,
or second, ring is much brighter, especially on the outer edge, and
shading off to the dusky edge next to the planet. There is no sign
of division into a third dusky innermost ring, as was plainly seen
by Bond. This, too, may be in a state of flux.

The markings of the planet are delicate, difficult of detection,
and are not like those stark zebra stripes that are so often
represented.

The distance between the planet and the second ring seems to be
diminished one-half since 1657, and this ring has doubled its breadth
in the same time. Some of this difference may be owing to our greater
telescopic power, enabling us to see the ring closer to the planet;
but in all probability the ring is closing in upon the central
body, and will touch it by A.D. 2150. Thus the whole ring must
ultimately fall upon the planet, instead of making a satellite.

We are anxious to learn the nature of such a ring. [Page 172]
Laplace mathematically demonstrated that it cannot be uniform and
solid, and survive. Professor Peirce showed it could not be fluid,
and continue. Then Professor Maxwell showed that it must be formed
of clouds of satellites too small to be seen individually, and too
near together for the spaces to be discerned, unless, perhaps, we
may except the inner dark ring, where they are not near enough to
make it positively luminous. Indeed, there is some evidence that the
meteoroids are far enough apart to make the ring partially
transparent.

We look forward to the opportunities for observation in 1882 with
the brightest hope that these difficult questions will be solved.

_Satellites of Saturn._

The first discovered satellite of Saturn seen by Huyghens was in
1655, and the last by the Bonds, father and son, of Cambridge,
in 1848. These are eight in number, and are named:

Distant from Saturn's centre.
I. Mimas 119,725 miles.
II. Enceladus 153,630 "
III. Tethys 190,225 "
IV. Dione 243,670 "
V. Rhea 340,320 "
VI. Titan 788,915 "
VII. Hyperion 954,160 "
VIII. Japetus 2,292,790 "

Titan can be seen by almost any telescope; I., II., and III., only
by the most powerful instrument. All except Japetus revolve nearly
in the plane of the ring. Like the moons of Jupiter, they present
remarkable and unaccountable variations of brilliancy. An inspection
[Page 173] of the table reveals either an expectation that another
moon will be discovered between V. and VI., and about three more
between VII. and VIII., or that these gaps may be filled with groups
of invisible asteroids, as the gap between Mars and Jupiter. This
will become more evident by drawing Saturn, the rings, and orbits of
the moons all as circles, on a scale of 10,000 miles to the inch.
Saturn will be in the centre, 70,000 miles in diameter; then a gap,
decreasing twenty-nine miles a year to the first ring, of, say,
10,000 miles; a dark ring 9000 miles wide; next the brightest ring
18,300 miles wide; then a gap of 1750 miles; then the outer ring
10,000 miles wide; then the orbits of the satellites in order.

If the scenery of Jupiter is magnificent, that of Saturn must be
sublime. If one could exist there, he might wander from the illuminated
side of the rings, under their magnificent arches, to the darkened
side, see the swift whirling moons; one of them presenting ten times
the disk of the earth's moon, and so very near as to enable him
to watch the advancing line of light that marks the lunar morning
journeying round that orb.

URANUS.

Sign [Symbol]; the initial of Herschel, and sign of the world.

DISTANCE FROM THE SUN, 1,771,000,000 MILES. DIAMETER, 31,700 MILES.
AXIAL REVOLUTION UNKNOWN. ORBITAL, 84 YEARS. VELOCITY PER MINUTE,
252 MILES. MOONS, FOUR.

Uranus was presented to the knowledge of man as an unexpected reward
for honest work. It was first mistaken by its discoverer for a comet,
a mere cloud of vapor; but it proved to be a world, and extended the
[Page 174] boundaries of our solar system, in the moment of its
discovery, as much as all investigation had done in all previous
ages.

Sir William Herschel was engaged in mapping stars in 1781, when he
first observed its sea-green disk. He proposed to call it _Georgium
Sidus_, in honor of his king; but there were too many names of the
gods in the sky to allow a mortal name to be placed among them. It
was therefore called Uranus, since, being the most distant body of
our system, as was supposed, it might appropriately bear the name
of the oldest god. Finding anything in God's realms of infinite
riches ought not to lead men to regard that as final, but as a
promise of more to follow.

This planet had been seen five times by Flamsteed before its character
was determined--once nearly a century before--and eight times by
Le Monnier. These names, which might easily have been associated
with a grand discovery, are associated with careless observation.
Eyes were made not only to be kept open, but to have minds behind
them to interpret their visions. Herschel thought he discovered six
moons belonging to Uranus, but subsequent investigation has limited
the number to four. Two of these are seen with great difficulty by
the most powerful telescopes.

If the plane of our moon's orbit were tipped up to a greater
inclination, revolving it on the line of nodes as an axis until
it was turned 85 deg., the moon, still continuing on its orbit in that
plane, would go over the poles instead of about the equator, and
would go back to its old path when the plane was revolved 180 deg.;
but its revolution would now be from east to west, or [Page 175]
retrograde. The plane of the moons of Uranus has been thus inclined
till it has passed 10 deg. beyond the pole, and the moons' motions are
retrograde as regards other known celestial movements. How Uranus
itself revolves is not known. There are more worlds to conquer.

NEPTUNE.

God of the sea; sign [Symbol], his trident.

DISTANCE FROM THE SUN, 2,775,000,000 MILES. DIAMETER, 34,500 MILES.
VELOCITY PER MINUTE, 201.6 MILES. AXIAL REVOLUTION UNKNOWN. ORBITAL,
164.78 YEARS. ONE MOON.

Men sought for Neptune as the heroes sought the golden fleece.
The place of Uranus had been mapped for nearly one hundred years
by these accidental observations. On applying the law of universal
gravitation, a slight discrepancy was found between its computed
place and its observed place. This discrepancy was exceedingly
slight. In 1830 it was only 20"; in 1840,190"; in 1884, 2'. Two
stars that were 2' apart would appear as one to the keenest unaided
eye, but such an error must not exist in astronomy. Years of work
were given to its correction. Mr. John C. Adams, of Cambridge,
England, finding that the attraction of a planet exterior to Uranus
would account for its irregularities, computed the place of such
a hypothetical body with singular exactness in October, 1841; but
neither he nor the royal astronomer Airy looked for it. Another
opportunity for immortality was heedlessly neglected. Meanwhile,
M. Leverrier, of Paris, was working at the same problem. In the
summer of 1846 Leverrier announced the place of the exterior planet.
The conclusion was in striking coincidence with that of Mr. [Page
176] Clark. Mr. Challis commenced to search for the planet near the
indicated place, and actually saw and mapped the star August 4th,
1846, but did not recognize its planetary character. Dr. Galle, of
Berlin, on the 23d of September, 1846, found an object with a
planetary disk not plotted on the map of stars. It was the
sought-for world. It would seem easy to find a world seventy-six
times as large as the earth, and easy to recognize it when seen. The
fact that it could be discovered only by such care conveys an
overwhelming idea of the distance where it moves.

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