THE MOUNTAINS AND PLAINS OF THE MOON, AND THE SPECTACLES OF THE SUN
"... the Moon, whose orb
The Tuscan artist views through optic glass
At evening from the top of Fesole,
Or in Valdarno, to descry new lands,
Rivers or mountains in her spotty globe."--PARADISE LOST.
The moon is probably the most interesting of all telescopic objects.
This arises from its comparative nearness to the earth. A telescope
magnifying 1,000 diameters brings the moon within an apparent distance
of less than 240 miles. If telescopes are ever made with a magnifying
power of 10,000 diameters, then, provided that atmospheric difficulties
can be overcome, we shall see the moon as if it were only about twenty
miles off, and a sensitive astronomer might be imagined to feel a little
hesitation about gazing so closely at the moon--as if he were peering
into a neighbor world's window.
But a great telescope and a high magnifying power are not required to
interest the amateur astronomer in the study of the moon. Our three-inch
telescope is amply sufficient to furnish us with entertainment for many
an evening while the moon is running through its phases, and we shall
find delight in frequently changing the magnifying power as we watch the
lunar landscapes, because every change will present them in a different
aspect.
It should be remembered that a telescope, unless a terrestrial eyepiece
or prism is employed, reverses such an object as the moon top for
bottom. Accordingly, if the moon is on or near the meridian when the
observations are made, we shall see the north polar region at the bottom
and the south polar region at the top. In other words, the face of the
moon as presented in the telescope will be upside down, north and south
interchanging places as compared with their positions in a geographical
map. But east and west remain unaltered in position, as compared with
such a map--i. e., the eastern hemisphere of the moon is seen on the
right and the western hemisphere on the left. It is the moon's western
edge that catches the first sunlight when "new moon" begins, and, as the
phase increases, passing into "first quarter" and from that to "full
moon," the illumination sweeps across the disk from west to east.
[Illustration: LUNAR CHART NO. 1, NORTHWEST QUARTER.]
The narrow sickle of the new moon, hanging above the sunset, is a
charming telescopic sight. Use a low power, and observe the contrast
between the bright, smooth round of the sunward edge, which has almost
the polish of a golden rim, and the irregular and delicately shaded
inner curve, where the adjacent mountains and plains picturesquely
reflect or subdue the sunshine. While the crescent grows broader new
objects are continually coming into view as the sun rises upon them,
until at length one of the most conspicuous and remarkable of the lunar
"seas," the _Mare Crisium_, or Sea of Crises, lies fully displayed amid
its encircling peaks, precipices, and craters. The _Mare Crisium_ is all
in the sunlight between the third and fourth day after "new moon." It is
about 350 by 280 miles in extent, and if ever filled with water must
have been a very deep sea, since its arid bed lies at a great but not
precisely ascertained depth below the general level of the moon. There
are a few small craters on the floor of the _Mare Crisium_, the largest
bearing the name of Picard, and its borders are rugged with mountains.
On the southwestern side is a lofty promontory, 11,000 feet in height,
called Cape Agarum. At the middle of the eastern side a kind of bay
opens deep in the mountains, whose range here becomes very narrow.
Southeast of this bay lies a conspicuous bright point, the crater
mountain Proclus, on which the sun has fully risen in the fourth day of
the moon, and which reflects the light with extraordinary liveliness.
Adjoining Proclus on the east and south is a curious, lozenge-shaped
flat, broken with short, low ridges, and possessing a most peculiar
light-brown tint, easily distinguished from the general color tone of
the lunar landscapes. It would be interesting to know what was passing
in the mind of the old astronomer who named this singular region _Palus
Somnii_. It is not the only spot on the moon which has been called a
"marsh," and to which an unexplained connection with dreams has been
ascribed.
Nearly on the same meridian with Proclus, at a distance of about a
hundred miles northward, lies a fine example of a ring mountain, rather
more than forty miles in diameter, and with peak-tipped walls which in
some places are 13,000 feet in height, as measured from the floor
within. This is Macrobius. There is an inconspicuous central mountain in
the ring.
North of the _Mare Crisium_, and northwest of Macrobius, we find a much
larger mountain ring, oblong in shape and nearly eighty miles in its
greatest diameter. It is named Cleomenes. The highest point on its wall
is about 10,000 feet above the interior. Near the northeast corner of
the wall yawns a huge and very deep crater, Tralles, while at the
northern end is another oblong crater mountain called Burckhardt.
From Cleomenes northward to the pole, or to the northern extremity of
the crescent, if our observations are made during new moon, the ground
appears broken with an immense number of ridges, craters, and mountain
rings, among which we may telescopically wander at will. One of the more
remarkable of these objects, which may be identified with the aid of
Lunar Chart No. 1, is the vast ringed plain near the edge of the disk,
named Gauss. It is more than a hundred and ten miles in diameter. Owing
to its situation, so far down the side of the lunar globe, it is
foreshortened into a long ellipse, although in reality it is nearly a
circle. A chain of mountains runs north and south across the interior
plain. Geminus, Berzelius, and Messala are other rings well worth
looking at. The remarkable pair called Atlas and Hercules demand more
than passing attention. The former is fifty-five and the latter
forty-six miles in diameter. Each sinks 11,000 feet below the summit of
the loftiest peak on its encircling wall. Both are full of interesting
detail sufficient to occupy the careful observer for many nights. The
broad ring bearing the name of Endymion is nearly eighty miles in
diameter, and has one peak 15,000 feet high. The interior plain is flat
and dark. Beyond Endymion on the edge of the disk is part of a gloomy
plain called the _Mare Humboltianum_.
After glancing at the crater-shaped mountains on the western and
southern border of the _Mare Crisium_, Alhazen, Hansen, Condorcet,
Firmicus, etc., we pass southward into the area covered in Lunar Chart
No. 2. The long dark plain south of the _Mare Crisium_ is the _Mare
Fecunditatis_, though why it should have been supposed to be
particularly fecund, or fertile, is by no means clear. On the western
border of this plain, about three hundred miles from the southern end of
the _Mare Crisium_, is the mountain ring, or circumvallation, called
Langrenus, about ninety miles across and in places 10,000 feet high.
There is a fine central mountain with a number of peaks. Nearly a
hundred miles farther south, on the same meridian, lies an equally
extensive mountain ring named Vendelinus. The broken and complicated
appearance of its northern walls will command the observer's attention.
Another similar step southward, and still on the same meridian brings us
to a yet finer mountain ring, slightly larger than the others, and still
more complicated in its walls, peaks, and terraces, and in its
surroundings of craters, gorges, and broken ridges. This is Petavius.
West of Petavius, on the very edge of the disk, is a wonderful
formation, a walled plain named Humboldt, which is looked down upon at
one point near its eastern edge by a peak 16,000 feet in height. About a
hundred and forty miles south of Petavius is the fourth great mountain
ring lying on the same meridian. Its name is Furnerius. Look
particularly at the brilliantly shining crater on the northeast slope of
the outer wall of Furnerius.
[Illustration: LUNAR CHART NO. 2, SOUTHWEST QUARTER.]
Suppose that our observations are now interrupted, to be resumed when
the moon, about "seven days old," is in its first quarter. If we had
time, it would be a most interesting thing to watch the advance of the
lunar sunrise every night, for new beauties are displayed almost from
hour to hour; but, for the purposes of our description it is necessary
to curtail the observations. At first quarter one half of the lunar
hemisphere which faces the earth is illuminated by the sun, and the line
of sunrise runs across some of the most wonderful regions of the moon.
We begin, referring once more to Lunar Chart No. 1, in the neighborhood
of the north pole of the moon. Here the line along which day and night
meet is twisted and broken, owing to the roughness of the lunar surface.
About fifteen degrees southwest of the pole lies a remarkable
square-cornered, mountain-bordered plain, about forty miles in length,
called Barrow. Very close to the pole is a ring mountain, about
twenty-five miles in diameter, whose two loftiest peaks, 8,000 to 9,000
feet high, according to Neison, must, from their situation, enjoy
perpetual day.
The long, narrow, dark plain, whose nearest edge is about thirty degrees
south of the pole, is the _Mare Frigoris_, bordered on both sides by
uplands and mountains. At its southern edge we find the magnificent
Aristoteles, a mountain ring, sixty miles across, whose immense wall is
composed of terraces and ridges running up to lofty peaks, which rise
nearly 11,000 feet above the floor of the valley. About a hundred miles
south of Aristoteles is Eudoxus, another fine mountain ring, forty miles
in diameter, and quite as deep as its northern neighbor. These two make
a most striking spectacle.
We are now in the neighborhood of the greatest mountain chains on the
moon, the lunar Alps lying to the east and the lunar Caucasus to the
south of Aristoteles and Eudoxus, while still farther south, separated
from the Caucasus by a strait not more than a hundred miles broad,
begins the mighty range of the lunar Apennines. We first turn the
telescope on the Alps. As the line of sunrise runs directly across their
highest peaks, the effect is startling. The greatest elevations are
about 12,000 feet. The observer's eye is instantly caught by a great
valley, running like a furrow through the center of the mountain mass,
and about eighty or ninety miles in length. The sealike expanse south
and southeast of the Alps is the _Mare Imbrium_, and it is along the
coast of this so-called sea that the Alps attain their greatest height.
The valley, or gorge, above mentioned, appears to cut through the
loftiest mountains and to reach the "coast," although it is so narrowed
and broken among the greater peaks that its southern portion is almost
lost before it actually reaches the _Mare Imbrium_. Opening wider again
as it enters the _Mare_, it forms a deep bay among precipitous
mountains.
The Caucasus Mountains are not so lofty nor so precipitous as the Alps,
and consequently have less attraction for the observer. They border the
dark, oval plain of the _Mare Serenitatis_ on its northeastern side. The
great bay running out from the _Mare_ toward the northwest, between the
Caucasus and the huge mountain ring of Posidonius, bears the fanciful
name of _Lacus Somniorum_. In the old days when the moon was supposed to
be inhabited, those terrestrial godfathers, led by the astronomer
Riccioli, who were busy bestowing names upon the "seas" and mountains of
our patient satellite, may have pleased their imagination by picturing
this arm of the "Serene Sea" as a peculiarly romantic sheet of water,
amid whose magical influences the lunar gentlefolk, drifting softly in
their silver galleons and barges, and enjoying the splendors of "full
earth" poured upon their delightful little world, were accustomed to
fall into charming reveries, as even we hard-headed sons of Adam
occasionally do when the waters under the keel are calm and smooth and
the balmy air of a moonlit night invokes the twin spirits of poetry and
music.
Posidonius, the dominating feature of the shore line here, is an
extraordinary example of the many formations on the moon which are so
different from everything on the earth that astronomers do not find it
easy to bestow upon them names that truly describe them. It may be
called a ring mountain or a ringed plain, for it is both. Its diameter
exceeds sixty miles, and the interior plain lies about 2,000 feet below
the outer surface of the lunar ground. The mountain wall surrounding the
ring is by no means remarkable for elevation, its greatest height not
exceeding 6,000 feet, but, owing to the broad sweep of the curved walls,
the brightness of the plain they inclose, and the picturesque
irregularity of the silhouette of shadow thrown upon the valley floor by
the peaks encircling it, the effect produced upon the observer is very
striking and attractive.
Having finished with Posidonius and glanced across the broken region of
the Taurus Mountains toward the west, we turn next to consider the _Mare
Serenitatis_. This broad gray plain, which, with a slight magnifying
power, certainly looks enough like a sea to justify the first
telescopists in thinking that it might contain water, is about 430 by
425 miles in extent, its area being 125,000 square miles. Running
directly through its middle, nearly in a north and south line, is a
light streak, which even a good opera glass shows. This streak is the
largest and most wonderful of the many similar rays which extend on all
sides from the great crater, or ring, of Tycho in the southern
hemisphere. The ray in question is more than 2,000 miles long, and, like
its shorter congeners, it turns aside for nothing; neither "sea," nor
peak, nor mountain range, nor crater ring, nor gorge, nor canon, is able
to divert it from its course. It ascends all heights and drops into all
depths with perfect indifference, but its continuity is not broken. When
the sun does not illuminate it at a proper angle, however, the
mysterious ray vanishes. Is it a metallic vein, or is it volcanic lava
or ash? Was the globe of the moon once split open along this line?
The _Mare Serenitatis_ is encircled by mountain ranges to a greater
extent than any of the other lunar "seas." On its eastern side the
Caucasus and the Apennines shut it in, except for a strait a hundred
miles broad, by means of which it is connected with the _Mare Imbrium_.
On the south the range of the Haemus Mountains borders it, on the north
and northwest the Caucasus and the Taurus Mountains confine it, while on
the west, where again it connects itself by a narrow strait with another
"sea," the _Mare Tranquilitatis_, it encounters the massive uplift of
Mount Argaeus. Not far from the eastern strait is found the remarkable
little crater named Linne, not conspicuous on the gray floor of the
_Mare_, yet easily enough found, and very interesting because a
considerable change of form seems to have come over this crater some
time near the middle of the nineteenth century. In referring to it as a
crater it must not be forgotten that it does not form an opening in the
top of a mountain. In fact, the so-called craters on the moon, generally
speaking, are simply cavities in the lunar surface, whose bottoms lie
deep below the general level, instead of being elevated on the summit of
mountains, and inclosed in a conical peak. In regard to the alleged
change in Linne, it has been suggested, not that a volcanic eruption
brought it about, but that a downfall of steep walls, or of an
unsupported rocky floor, was the cause. The possibility of such an
occurrence, it must be admitted, adds to the interest of the observer
who regularly studies the moon with a telescope.
Just on the southern border of the _Mare_, the beautiful ring Menelaus
lies in the center of the chain of the Haemus Mountains. The ring is
about twenty miles across, and its central peak is composed of some
highly reflecting material, so that it shines very bright. The streak or
ray from Tycho which crosses the _Mare Serenitatis_ passes through the
walls of Menelaus, and perhaps the central peak is composed of the same
substance that forms the ray. Something more than a hundred miles
east-southeast from Menelaus, in the midst of the dark _Mare Vaporum_,
is another brilliant ring mountain which catches the eye, Manilius. It
exceeds Menelaus in brightness as well as in size, its diameter being
about twenty-five miles. There is something singular underlying the dark
lunar surface here, for not only is Manilius extraordinarily brilliant
in contrast with the surrounding plain, but out of that plain, about
forty miles toward the east, projects a small mountain which is also
remarkable for its reflecting properties, as if the gray ground were
underlain by a stratum of some material that flashes back the sunlight
wherever it is exposed. The crater mountain, Sulpicius Gallus, on the
border of the _Mare_, north of Manilius and east of Menelaus, is another
example of the strange shining quality of certain formations on the
moon.
Follow next the Haemus range westward until the attention falls upon the
great ring mountain Plinius, more than thirty miles across, and bearing
an unusual resemblance to a fortification. Mr. T. G. Elger, the
celebrated English selenographer, says of Plinius that, at sunrise, "it
reminds one of a great fortress or redoubt erected to command the
passage between the _Mare Tranquilitatis_ and the _Mare Serenitatis_."
But, of course, the resemblance is purely fanciful. Men, even though
they dwelt in the moon, would not build a rampart 6,000 feet high!
Mount Argaeus, at the southwest corner of the _Mare Serenitatis_, is a
very wonderful object when the sun has just risen upon it. This occurs
five days after the new moon.
Returning to the eastern extremity of the _Mare_, we glance, in passing,
at the precipitous Mount Hadley, which rises more than 15,000 feet above
the level of the _Mare_ and forms the northern point of the Apennine
range. Passing into the region of the _Mare Imbrium_, whose western end
is divided into the _Palus Putredinis_ on the south and the _Palus
Nebularum_ on the north, we notice three conspicuous ring mountains,
Cassini near the Alps, and Aristillus and Autolycus, a beautiful pair,
nearly opposite the strait connecting the two _Maria_. Cassini is
thirty-six miles in diameter, Aristillus thirty-four, and Autolycus
twenty-three. The first named is shallow, only 4,000 feet in depth from
the highest point of its wall, while Aristillus carries some peaks on
its girdle 11,000 feet high. Autolycus, like Cassini, is of no very
great depth.
Westward from the middle of an imaginary line joining Aristillus and
Cassini is the much smaller crater Theaetetus. Outside the walls of this
are a number of craterlets, and a French astronomer, Charbonneaux, of
the Meudon Observatory, reported in December, 1900, that he had
repeatedly observed white clouds appearing and disappearing over one of
these small craters.
South of the _Mare Vaporum_ are found some of the most notable of those
strange lunar features that are called "clefts" or "rills." Two crater
mountains, in particular, are connected with them, Ariadaeus at the
eastern edge of the _Mare Tranquilitatis_ and Hyginus on the southern
border of the _Mare Vaporum_. These clefts appear to be broad and deep
chasms, like the canons cut by terrestrial rivers, but it can not be
believed that the lunar canons are the work of rivers. They are rather
cracks in the lunar crust, although their bottoms are frequently
visible. The principal cleft from Ariadaeus runs eastward and passes
between two neighboring craters, the southern of which is named
Silberschlag, and is noteworthy for its brightness. The Hyginus cleft is
broader and runs directly through the crater ring of that name.
The observer will find much to interest him in the great, irregular, and
much-broken mountain ring called Julius Caesar, as well as in the ring
mountains, Godin, Agrippa, and Triesnecker. The last named, besides
presenting magnificent shadows when the sunlight falls aslant upon it,
is the center of a complicated system of rills, some of which can be
traced with our five-inch glass.
We next take up Lunar Chart No. 2, and pay a telescopic visit to the
southwestern quarter of the lunar world. The _Mare Tranquilitatis_
merges through straits into two southern extensions, the _Mare
Fecunditatis_ and the _Mare Nectaris_. The great ring mountains or
ringed plains, Langrenus, Vendelinus, Petavius, and Furnerius, all lying
significantly along the same lunar meridian, have already been noticed.
Their linear arrangement and isolated position recall the row of huge
volcanic peaks that runs parallel with the shore of the Pacific Ocean in
Oregon and Washington--Mount Jefferson, Mount Hood, Mount St. Helen's,
Mount Tacoma--but these terrestrial volcanoes, except in elevation, are
mere pins' heads in the comparison.
In the eastern part of the _Mare Fecunditatis_ lies a pair of relatively
small craters named Messier, which possess particular interest because
it has been suspected, though not proved, that a change of form has
occurred in one or other of the pair. Maedler, in the first half of the
nineteenth century, represented the two craters as exactly alike in all
respects. In 1855 Webb discovered that they are not alike in shape, and
that the easternmost one is the larger, and every observer easily sees
that Webb's description is correct. Messier is also remarkable for the
light streak, often said to resemble a comet's tail, which extends from
the larger crater eastward to the shore of the _Mare Fecunditatis_.
Goclenius and Guttemberg, on the highland between the _Mare
Fecunditatis_ and the _Mare Nectaris_, are intersected and surrounded by
clefts, besides being remarkable for their broken and irregular though
lofty walls. Guttemberg is forty-five miles and Goclenius twenty-eight
miles in diameter. The short mountain range just east of Guttemberg, and
bordering a part of the _Mare Nectaris_ on the west, is called the
Pyrenees.
The _Mare Nectaris_, though offering in its appearance no explanation of
its toothsome name--perhaps it was regarded as the drinking cup of the
Olympian gods--is one of the most singular of the dark lunar plains in
its outlines. At the south it ends in a vast semicircular bay, sixty
miles across, which is evidently a half-submerged mountain ring. But
submerged by what? Not water, but perhaps a sea of lava which has now
solidified and forms the floor of the _Mare Nectaris_. The name of this
singular formation is Fracastorius. Elger has an interesting remark
about it.
"On the higher portion of the interior, near the center," he says, "is a
curious object consisting apparently of four light spots, arranged in a
square, with a craterlet in the middle, all of which undergo notable
changes of aspect under different phases."
Other writers also call attention to the fine markings, minute
craterlets, and apparently changeable spots on the floor of
Fracastorius.
We go now to the eastern side of the _Mare Nectaris_, where we find one
of the most stupendous formations in the lunar world, the great mountain
ring of Theophilus, noticeably regular in outline and perfect in the
completeness of its lofty wall. The circular interior, which contains in
the center a group of mountains, one of whose peaks is 6,000 feet high,
sinks 10,000 feet below the general level of the moon outside the wall!
One of the peaks on the western edge towers more than 18,000 feet above
the floor within, while several other peaks attain elevations of 15,000
to 16,000 feet. The diameter of the immense ring, from crest to crest of
the wall, is sixty-four miles. Theophilus is especially wonderful on the
fifth and sixth days of the moon, when the sun climbs its shining
pinnacles and slowly discloses the tremendous chasm that lies within its
circles of terrible precipices.
On the southeast Theophilus is connected by extensions of its walls with
a shattered ring of vast extent called Cyrillus; and south from
Cyrillus, and connected with the same system of broken walls, lies the
still larger ring named Catharina, whose half-ruined walls and numerous
crater pits present a fascinating spectacle as the shadows retreat
before the sunrise advancing across them. These three--Theophilus,
Cyrillus, and Catharina--constitute a scene of surpassing magnificence,
a glimpse of wonders in another world sufficient to satisfy the most
riotous imagination.
South of the _Mare Nectaris_ the huge ring mountain of Piccolomini
attracts attention, its massive walls surrounding a floor nearly sixty
miles across, and rising in some places to an altitude of nearly 15,000
feet. It should be understood that wherever the height of the mountain
wall of such a ring is mentioned, the reference level is that of the
interior plain or floor. The elevation, reckoned from the outer side, is
always very much less.
The entire region south and east of Theophilus and its great neighbors
is marvelously rough and broken. Approaching the center of the moon, we
find a system of ringed plains even greater in area than any of those we
have yet seen. Hipparchus is nearly a hundred miles long from north to
south, and nearly ninety miles broad from east to west. But its walls
have been destroyed to such an extent that, after all, it yields in
grandeur to a formation like Theophilus.
Albategnius is sixty-five miles across, with peaks from 10,000 to 15,000
feet in height. Sacrobosco is a confused mass of broken and distorted
walls. Aliacensis is remarkable for having a peak on the eastern side of
its wall which is more than 16,000 feet high. Werner, forty-five miles
in diameter, is interesting because under its northeastern wall Maedler,
some seventy years ago, saw a light spot of astonishing brightness,
unmatched in that respect by anything on the moon except the peak of
Aristarchus, which we shall see later. This spot seems afterward to have
lost brilliance, and the startling suggestion has been made that its
original brightness might have been due to its then recent deposit from
a little crater that lies in the midst of it. Walter is of gigantic
dimensions, about one hundred miles in diameter. Unlike the majority of
the ringed plains, it departs widely from a circle. Stoefler is yet
larger than Walter; but most interesting of all these gigantic
formations is Maurolycus, whose diameter exceeds one hundred and fifty
miles, and which has walls 13,000 or 14,000 feet high. Yet, astonishing
though it may seem, this vast and complicated mass of mountain walls,
craters, and peaks, is virtually unseen at full moon, owing to the
perpendicularity of the sunlight, which prevents the casting of shadows.
We shall next suppose that another period of about seven days has
elapsed, the moon in the meantime reaching its full phase. We refer for
guidance to Lunar Chart No. 3. The peculiarity of the northeastern
quadrant which immediately strikes the eye is the prevalence of the
broad plains called _Maria_, or "seas." The northern and central parts
are occupied by the _Mare Imbrium_, the "Sea of Showers" or of "Rains,"
with its dark bay the _Sinus AEstuum_, while the eastern half is covered
by the vast _Oceanus Procellarum_, the "Ocean of Storms" or of
"Tempests."
Toward the north a conspicuous oval, remarkably dark in hue, immediately
attracts our attention. It is the celebrated ringed plain of Plato,
about sixty miles in diameter and surrounded by a saw-edged rampart,
some of whose pinnacles are 6,000 or 7,000 feet high. Plato is a
favorite subject for study by selenographers because of the changes of
color which its broad, flat floor undergoes as the sun rises upon it,
and also because of the existence of enigmatical spots and streaks whose
visibility changes. South of Plato, in the _Mare Imbrium_, rises a
precipitous, isolated peak called Pico, 8,000 feet in height. Its
resemblance in situation to the conical mountain Pico in the Azores
strikes the observer.
[Illustration: LUNAR CHART NO. 3, NORTHEAST QUARTER.]
Eastward of Plato a line of highlands, separating the _Mare Imbrium_
from the _Mare Frigoris,_ carries the eye to the beautiful semicircular
_Sinus Iridum_, or "Bay of Rainbows." The northwestern extremity of
this remarkable bay is guarded by a steep and lofty promontory called
Cape Laplace, while the southeastern extremity also has its towering
guardian, Cape Heraclides. The latter is interesting for showing,
between nine and ten days after full moon, a singularly perfect profile
of a woman's face looking out across the _Mare Imbrium_. The winding
lines, like submerged ridges, delicately marking the floor of the _Sinus
Iridum_ and that of the _Mare_ beyond, are beautiful telescopic
objects. The "bay" is about one hundred and thirty-five miles long by
eighty-four broad.
The _Mare Imbrium_, covering 340,000 square miles, is sparingly dotted
over with craters. All of the more conspicuous of them are indicated in
the chart. The smaller ones, like Caroline Herschel, Helicon, Leverrier,
Delisle, etc., vary from eight to twelve miles in diameter. Lambert is
seventeen miles in diameter, and Euler nineteen, while Timocharis is
twenty-three miles broad and 7,000 feet deep below its walls, which rise
only 3,000 feet above the surface of the _Mare_.
Toward the eastern border of the sea, south of the Harbinger Mountains,
we find a most remarkable object, the mountain ring, or crater plain,
called Aristarchus. This ring is not quite thirty miles in diameter, but
there is nothing on the moon that can compare with it in dazzling
brilliance. The central peak, 1,200 or 1,300 feet high, gleams like a
mountain of crusted snow, or as if it were composed of a mass of
fresh-broken white metal, or of compacted crystals. Part of the inner
slope of the east wall is equally brilliant. In fact, so much light is
poured out of the circumvallation that the eye is partially blinded, and
unable distinctly to see the details of the interior. No satisfactory
explanation of the extraordinary reflecting power of Aristarchus has
ever been offered. Its neighbor toward the east, Herodotus, is somewhat
smaller and not remarkably bright, but it derives great interest from
the fact that out of a breach in its northern wall issues a vast cleft,
or chasm, which winds away for nearly a hundred miles across the floor
of the _Mare_, making an abrupt turn when it reaches the foot of the
Harbinger Mountains.
The comparatively small crater, Lichtenberg, near the northeastern limb
of the moon, is interesting because Maedler used to see in its
neighborhood a pale-red tint which has not been noticed since his day.
Returning to the western side of the quadrant represented in Lunar Chart
No. 3, we see the broad and beautifully regular ringed plain of
Archimedes, fifty miles in diameter and 4,000 feet deep.
A number of clefts extend between the mountainous neighborhood of
Archimedes and the feet of the gigantic Apennine Mountains on the
southwest. The little double crater, Beer, between Archimedes and
Timocharis, is very bright.
The Apennines extend about four hundred and eighty miles in a
northwesterly and southeasterly direction. One of their peaks near the
southern end of the range, Mount Huygens, is at least 18,000 feet high,
and the black silhouettes of their sharp-pointed shadows thrown upon the
smooth floor of the _Mare Imbrium_ about the time of first quarter
present a spectacle as beautiful as it is unique. The Apennines end at
the southeast in the ring mountain, Eratosthenes, thirty-eight miles
across and very deep, one of its encircling chain of peaks rising 16,000
feet above the floor, and about half that height above the level of the
_Mare Imbrium_. The shadows cast by Eratosthenes at sunrise are
magnificent.
And now we come to one of the supreme spectacles of the moon, the
immense ring or crater mountain Copernicus. This is generally regarded
as the grandest object that the telescope reveals on the earth's
satellite. It is about fifty-six miles across, and its interior falls to
a depth of 8,000 feet below the _Mare Imbrium_. Its broad wall, composed
of circle within circle of ridges, terraces, and precipices, rises on
the east about 12,000 feet above the floor. On the inner side the slopes
are very steep, cliff falling below cliff, until the bottom of the
fearful abyss is attained. To descend those precipices and reach the
depressed floor of Copernicus would be a memorable feat for a
mountaineer. In the center of the floor rises a complicated mountain
mass about 2,400 feet high. All around Copernicus the surface of the
moon is dotted with countless little crater pits, and splashed with
whitish streaks. Northward lie the Carpathian Mountains, terminating on
the east in Tobias Mayer, a ring mountain more than twenty miles across.
The mountain ring Kepler, which is also the center of a great system of
whitish streaks and splashes, is twenty-two miles in diameter, and
notably brilliant.
Finally, we turn to the southeastern quadrant of the moon, represented
in Lunar Chart No. 4. The broad, dark expanse extending from the north
is the _Mare Nubium_ on the west and the _Oceanus Procellarum_ on the
east. Toward the southeast appears the notably dark, rounded area of the
_Mare Humorum_ inclosed by highlands and rings. We begin with the range
of vast inclosures running southward near the central meridian, and
starting with Ptolemaeus, a walled plain one hundred and fifteen miles in
its greatest diameter and covering an area considerably exceeding that
of the State of Massachusetts. Its neighbor toward the south, Alphonsus,
is eighty-three miles across. Next comes Arzachel, more than sixty-five
miles in diameter. Thebit, more than thirty miles across, is very deep.
East of Thebit lies the celebrated "lunar railroad," a straight,
isolated wall about five hundred feet high and sixty-five miles long,
dividing at its southern end into a number of curious branches, forming
the buttresses of a low mountain. Purbach is sixty miles broad, and
south of that comes a wonderful region where the ring mountains Hell,
Ball, Lexell, and others, more or less connected with walls, inclose an
area even larger than Ptolemaeus, but which, not being so distinctly
bordered as some of the other inclosed plains, bears no distinctive
name.
[Illustration: LUNAR CHART NO. 4, SOUTHEAST QUARTER.]
The next conspicuous object toward the south ranks with Copernicus among
the grandest of all lunar phenomena--the ring, or crater, Tycho. It is
about fifty-four miles in diameter and some points on its wall rise
17,000 feet above the interior. In the center is a bright mountain peak
5,000 feet high. But wonderful as are the details of its mountain ring,
the chief attraction of Tycho is its manifest relation to the mysterious
bright rays heretofore referred to, which extend far across the surface
of the moon in all directions, and of which it is the center. The
streaks about Copernicus are short and confused, constituting rather a
splash than a regular system of rays; but those emanating from Tycho are
very long, regular, comparatively narrow, and form arcs of great circles
which stretch away for hundreds of miles, allowing no obstacle to
interrupt their course.
Southwest of Tycho lies the vast ringed plain of Maginus, a hundred
miles broad and very wonderful to look upon, with its labyrinth of
formations, when the sun slopes across it, and yet, like Maurolycus,
invisible under a vertical illumination. "The full moon," to use
Maedler's picturesque expression, "knows no Maginus." Still larger and
yet more splendid is Clavius, which exceeds one hundred and forty miles
in diameter and covers 16,000 square miles of ground within its fringing
walls, which carry some of the loftiest peaks on the moon, several
attaining 17,000 feet. The floor is deeply depressed, so that an
inhabitant of this singular inclosure, larger than Massachusetts,
Connecticut, and Rhode Island combined, would dwell in land sunk two
miles below the general level of the world about him.
In the neighborhood of the south pole lies the large walled plain of
Newton, whose interior is the deepest known depression on the moon. It
is so deep that the sunshine never touches the larger part of the floor
of the inner abyss, and a peak on its eastern wall rises 24,000 feet
sheer above the tremendous pit. Other enormous walled plains are
Longomontanus, Wilhelm I, Schiller, Bailly, and Schickard. The latter is
one hundred and thirty-four miles long and bordered by a ring varying
from 4,000 to 9,000 feet in height. Wargentin, the oval close to the
moon's southeast limb, beyond Schickard, is a unique formation in that,
instead of its interior being sunk below the general level, it is
elevated above it. It has been suggested that this peculiarity is due to
the fact that the floor of Wargentin was formed by inflation from below,
and that it has cooled and solidified in the shape of a gigantic dome
arched over an immense cavity beneath. A dome of such dimensions,
however, could not retain its form unless partly supported from beneath.
Hainzel is interesting from its curious outline; Cichus for the huge
yawning crater on its eastern wall; Capuanus for a brilliant shining
crater also on its eastern wall; and Mercator for possessing bright
craters on both its east and its west walls. Vitello has a bright
central mountain and gains conspicuousness from its position at the edge
of the dark _Mare Humorum_. Agatharchides is the broken remnant of a
great ring mountain. Gassendi, an extremely beautiful object, is about
fifty-five miles across. It is encircled with broken walls, craters and
bright points, and altogether presents a very splendid appearance about
the eleventh day of the moon's age.
Letronne is a half-submerged ring, at the southern end of the _Oceanus
Procellarum_, which recalls Fracastorius in the western lunar
hemisphere. It lies, however, ten degrees nearer the equator than
Fracastorius. Billy is a mountain ring whose interior seems to have been
submerged by the dark substance of the _Oceanus Procellarum_, although
its walls have remained intact. Mersenius is a very conspicuous ring,
forty miles in diameter, east of the _Mare Humorum_. Vieta, fifty miles
across, is also a fine object. Grimaldi, a huge dusky oval, is nearly
one hundred and fifty miles in its greatest length. The ring mountain
Landsberg, on the equator, and near the center of the visible eastern
hemisphere, is worth watching because Elger noticed changes of color in
its interior in 1888.
Bullialdus, in the midst of the _Mare Nubium_, is a very conspicuous and
beautiful ring mountain about thirty-eight miles in diameter, with walls
8,000 feet high above the interior.
Those who wish to see the lunar mountains in all their varying aspects
will not content themselves with views obtained during the advance of
the sunlight from west to east, between "new moon" and "full moon," but
will continue their observations during the retreat of the sunlight from
east to west, after the full phase is passed.
It is evident that the hemisphere of the moon which is forever turned
away from the earth is quite as marvelous in its features as the part
that we see. It will be noticed that the entire circle of the moon's
limb, with insignificant interruptions, is mountainous. Possibly the
invisible side of our satellite contains yet grander peaks and crater
mountains than any that our telescopes can reach. This probability is
increased by the fact that the loftiest known mountain on the moon is
never seen except in silhouette. It is a member of a great chain that
breaks the lunar limb west of the south pole, and that is called the
Leibnitz Mountains. The particular peak referred to is said by some
authorities to exceed 30,000 feet in height. Other great ranges seen
only in profile are the Doerfel Mountains on the limb behind the ring
plain Bailly, the Cordilleras, east of Eichstadt, and the D'Alembert
Mountains beyond Grimaldi. The profile of these great mountains is
particularly fine when they are seen during an eclipse of the sun. Then,
with the disk of the sun for a background, they stand out with startling
distinctness.
THE SUN
When the sun is covered with spots it becomes a most interesting object
for telescopic study. Every amateur's telescope should be provided with
apparatus for viewing the sun. A dark shade glass is not sufficient and
not safe. What is known as a solar prism, consisting of two solid prisms
of glass, cemented together in a brass box which carries a short tube
for the eyepiece, and reflecting an image of the sun from their plane of
junction--while the major remnant of light and heat passes directly
through them and escapes from an opening provided for the
purpose--serves very well. Better and more costly is an apparatus called
a helioscope, constructed on the principle of polarization and provided
with prisms and reflectors which enable the observer, by proper
adjustment, to govern very exactly and delicately the amount of light
that passes into the eyepiece.
Furnished with an apparatus of this description we can employ either a
three-, four-, or five-inch glass upon the sun with much satisfaction.
For the amateur's purposes the sun is only specially interesting when it
is spotted. The first years of the twentieth century will behold a
gradual growth in the number and size of the solar spots as those years
happen to coincide with the increasing phase of the sun-spot period.
Large sun spots and groups of spots often present an immense amount of
detail which tasks the skill of the draughtsman to represent it. But a
little practice will enable one to produce very good representations of
sun spots, as well as of the whitish patches called faculae by which they
are frequently surrounded.
For the simple purpose of exhibiting the spotted face of the sun without
much magnifying power, a telescope may be used to project the solar
image on a white sheet or screen. If the experiment is tried in a room,
a little ingenuity will enable the observer to arrange a curtain
covering the window used, in such a way as to exclude all the light
except that which comes through the telescope. Then, by placing a sheet
of paper or a drawing board before the eyepiece and focusing the image
of the sun upon it, very good results may be obtained.
If one has a permanent mounting and a driving clock, a small
spectroscope may be attached, for solar observations, even to a
telescope of only four or five inches aperture, and with its aid most
interesting views may be obtained of the wonderful red hydrogen flames
that frequently appear at the edge of the solar disk.