Thomas Gwyn Elger - The Moon

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STADIUS.--An inconspicuous though a very interesting formation, 43 miles
in diameter, W. of Copernicus, with a border scarcely exceeding 200 feet
in height. Hence it is not surprising that it was for a long time
altogether overlooked by Madler. Except as a known object, it is only
traceable under very oblique illumination, and even then some attention
is required before its very attenuated wall can be followed all round. It
is most prominent on the W., where it apparently consists of a S.
extension of the Eratosthenes mountain-arm, and is associated with a
number of little craters and pits. This is succeeded on the S.W. by a
narrow strip of bright wall, and on the S. by a section made up of a
piece of straight wall and a strip curving inwards, forming the S. side.
On the E. the border assumes a very ghostly character, and appears to be
mainly defined by rows of small depressions and mounds. On the N.E., N.,
and N.W. it is still lower and narrower; so much so, that it is only for
an hour or so after sunrise or before sunset that it can be traced at
all. On every side, with the exception of the curved piece on the S., the
wall consists of linear sections. The interior contains a great number of
little craters and very low longitudinal mounds. Ten craters are shown in
Beer and Madler's map. Schmidt only draws fifteen, though in the text
accompanying his chart he says that he once counted fifty. In the
monograph published in the _Journal_ of the Liverpool Astronomical
Society (vol. v. part 8), forty-one are represented. They appear to be
rather more numerous on the S. half of the floor than elsewhere. Just
beyond the limits of the border on the N., is a bright crater with a much
larger obscure depression on the W. of it. The former is surrounded by a
multitude of minute craters and crater-cones, which are easily seen under
a low sun. Though almost every trace of Stadius disappears under a high
light, I have had little difficulty in seeing portions of the border and
some of the included details when the morning terminator had advanced as
far as the E. wall of Herodotus, and the site was traversed by
innumerable light streaks radiating from Copernicus. At this phase the
bright crater, just mentioned, on the N. edge of the border was tolerably
distinct.

COPERNICUS.--This is without question the grandest object, not only on
the second Quadrant, but on the whole visible superficies of the moon. It
undoubtedly owes its supremacy partly to its comparative isolation on the
surface of a vast plain, where there are no neighbouring formations to
vie with it in size and magnificence, but partly also to its favourable
position, which is such, that, though not central, is sufficiently
removed from the limb to allow all its manifold details to be critically
examined without much foreshortening. There are some other formations,
Langrenus and Petavius, for example, which, if they were equally well
situated, would probably be fully as striking; but, as we see it
Copernicus is _par excellence_ the monarch of the lunar ring-mountains.
Schmidt remarks that this incomparable object combines nearly all the
characteristics of the other ring-plains, and that careful study directed
to its unequalled beauties and magnificent form is of much more value
than that devoted to a hundred other objects of the same class. It is
fully 56 miles in diameter, and, though generally described as nearly
circular, exhibits very distinctly under high powers a polygonal outline,
approximating very closely to an equilateral hexagon. There are, however,
two sections of the crest of the border on the N.E. which are inflected
slightly towards the centre, a peculiarity already noticed in the case of
Eratosthenes. The walls, tolerably uniform in height, are surmounted by a
great number of peaks, one of which on the W., according to Neison,
stands 11,000 feet above the floor, and a second on the opposite side is
nearly as high. Both the inner and outer slopes of this gigantic rampart
are very broad, each being fully 10 miles in width. The outer slope,
especially on the E., is a fine object at sunrise, when its rugged
surface, traversed by deep gullies, is seen to the best advantage. The
terraces and other features on the bright inner declivities on this side
may be well observed when the sun's altitude is about 6 deg. Schmidt,
whose measures differ from those of Neison, estimates the height of the
wall on the E. to be 12,000 feet, and states that the interior slopes
vary from 60 deg. to 50 deg. above, to from 10 deg. to 2 deg. at the
base. The first inclination of 50 deg., and in some cases of 60 deg., is
confined to the loftiest steep crests and to the flanks of the terraces.
There are apparently five bright little mountains on the floor, the most
easterly being rather the largest, and a great number of minute hillocks
on the S.E. quarter. S.W. of the centre is a little crater, and on the
same side of the interior a curious hook-shaped ridge, projecting from
the foot of the wall, and extending nearly halfway across the floor. The
region surrounding Copernicus is one of the most remarkable on the moon,
being everywhere traversed by low ridges, enclosing irregular areas,
which are covered with innumerable craterlets, hillocks, and other minute
features, and by a labyrinth of bright streaks, extending for hundreds of
miles on every side, and varying considerably both in width and
brilliancy.

The notable crater-row on the W., often utilised by observers for testing
the steadiness of the air and the definition of their telescopes, should
be examined when it is on the morning terminator, at which time Webb's
homely comparison, "a mole-run with holes in it," will be appreciated,
and its evident connection with the E. side of Stadius clearly made out.
There is another much more delicate row running closely parallel to this
object; it lies a little W. of it, and extends farther in a northerly
direction.

ARCHIMEDES.--Next to Plato the finest object on the Mare Imbrium. It is
about 50 miles in diameter. The average height of its massive border is
about 4000 feet above the interior, which is only depressed some 500 or
600 feet below the Mare, the highest peak (about 7000 feet) being on the
S.E. The walls are terraced, and include much detail, both within and
without. The most noteworthy features in connection with this formation
are the crater-cones, craterlets, pits, white spots, and light streaks
which figure on the otherwise smooth interior. Mr. T.P. Gray, F.R.A.S.,
of Bedford, who, with praiseworthy assiduity, has devoted more than ten
years to the close scrutiny of these features, Mr. Stanley Williams, and
others, have detected four crater-cones on the E. half of the floor, and
about fifty minute craters and white spots, also probably volcanic vents,
and a very curious and interesting series of light streaks, mostly
traversing the formation from E. to W. A little E. of the centre is a
dusky oval area about 6 miles across, and S.W. of this is another, much
smaller. Under some conditions of illumination the two principal light
markings may be traced over the W. wall, and for some distance on the
plain beyond.

On the southern side of Archimedes is a very rugged mountain region,
extending for more than 100 miles towards the south: on the W. of this
originates a remarkable rill-system, best seen under evening
illumination. The two principal clefts follow a nearly parallel course up
to the face of the Apennines near Mount Bradley, crossing in their way,
almost at right angles, other clefts which run at no great distance from
the E. foot of this range and ramify among the outlying hills. Archimedes
A is a brilliant little ring-plain on the S.E. of Archimedes. It casts an
extraordinary shadow at sunrise, and has a well-marked crater-row on the
E. of it, and two long narrow valleys, one of which appears to be a
southerly extension of the row.

BEER.--A very bright little crater, with an unnamed formation of about
the same size adjoining it on the N., with which is associated a curious
winding ridge that appears to traverse a gap in its N. wall.

TIMOCHARIS.--A fine ring-plain, 23 miles in diameter (the centre of a
minor ray-system). It stands isolated on the Mare Imbrium (below the
level of which it is depressed some 3000 feet), about midway between
Archimedes and Lambert. Its walls, rising about 7000 feet above the
floor, are conspicuously terraced, and on their W. outer slopes exhibit
some remarkable depressions. There is a distinct break on the N., and a
bright little crater on the N.W., connected with the foot of the _glacis_
by a prominent ridge. On the bright central mountain, Schmidt, in 1842,
detected a crater, which is easily seen under a moderately high light.
Timocharis and the neighbourhood, especially the peculiar shape of the
terminator on the E. of the formation, is well worth examination at
sunrise.

PIAZZI SMYTH.--A conspicuous little ring-plain, 5 or 6 miles in diameter,
depressed about 1500 feet below the Mare Imbrium, with a border rising
about 2000 feet above it. With the curious arrangement of ridges, of
which it is the apparent centre, it is a striking object under a low sun.

KIRCH.--A rather smaller object of the same class on the S.E.

PLATO.--This beautiful walled-plain, 60 miles in diameter, with its
bright border and dark steel-grey floor, has, from the time of Hevelius
to the present, been one of the most familiar objects to lunar observers.
In the rude maps of the seventeenth century it figures as the "Lacus
Niger Major," an appellation which not inaptly describes its appearance
under a high sun, when the sombre tone of its apparently smooth interior
is in striking contrast to that of the isthmus on which the formation
stands. It will repay observation under every phase, and though during
the last thirty years no portion of the moon has been more diligently
scrutinised than the floor; the neighbourhood includes a very great
number of objects of every kind, which, not having received so much
attention, will afford ample employment to the possessor of a good
telescope during many lunations.

The border of Plato, varying in height from 3000 to 4000 feet above the
interior, is crowned by several lofty peaks, the highest (7400 feet)
standing on the N. side of the curious little triangular formation on the
E. wall. Those on the W., three in number, reckoning from N. to S., are
respectively about 5000, 6000, and 7000 feet in altitude above the floor.
The circumvallation being very much broken and intersected by passes,
exhibits many distinct breaches of continuity, especially on the S. There
is a remarkable valley on the S.W., which, cutting through the border at
a wide angle, suddenly turns towards the S.E., and descends the slope of
the _glacis_ in a more attenuated form. Another but shorter valley is
traceable at sunrise on the W. On the N.W., the rampart is visibly
dislocated, and the gap occupied by an intrusive mountain mass. This
dislocation is not confined to the wall, but, under favourable
conditions, may be traced across the floor to the broken S.E. border. It
is probably a true "fault." On the N.E., the inner slope of the wall is
very broad, and affords a fine example of a vast landslip.

The spots and faint light markings on the floor are of a particularly
interesting character. During the years 1869 to 1871 they were
systematically observed and discussed under the auspices of the Lunar
Committee of the British Association. Among the forty or more spots
recorded, six were found to be crater-cones. The remainder--or at least
most of them--are extremely delicate objects, which vary in visibility in
a way that is clearly independent of libration or solar altitude; and,
what is also very suggestive, they are always found closely associated
with the light markings,--standing either upon the surface of these
features or close to their edges. Recent observations of these spots with
a 13 inch telescope by Professor W.H. Pickering, under the exceptionally
good conditions which prevail at Arequipa, Peru, have revived interest in
the subject, for they tend to show that visible changes have taken place
in the aspect of the principal crater-cones and of some of the other
spots since they were so carefully and zealously scrutinised nearly a
quarter of a century ago. The gradual darkening of the floor of Plato as
the sun's altitude increases from 20 deg. till after full moon may be
regarded as an established fact, though no feasible hypothesis has been
advanced to account for it.

On the N.E. of Plato is a large bright crater, A; and, extending in a
line from this towards the E., is a number of smaller rings, the whole
group being well worth examination. On the N. there is a winding cleft,
and some short crossed clefts in the rugged surface just beyond the foot
of the wall, which I have seen with a 4 inch achromatic. The region on
the W., imperfectly shown in the maps, includes much unrecorded detail.
On the Mare Imbrium S. of Plato is a large area enclosed by low ridges,
to which Schroter gave the name "Newton." It suggests the idea that it
represents the ruin of a once imposing enclosure, of which the
conspicuous mountain Pico formed a part.

TIMAEUS.--A very bright ring-plain, 22 miles in diameter, with walls
about 4500 feet in height, on the coast-line of the Mare Frigoris, and
associated with the E. side of the great enclosed plain W.C. Bond.
Schmidt shows a double hill, nearly central, and Neison a crater on the
S.W. wall.

BIRMINGHAM.--A large rhomboidal-shaped enclosure, defined by mountain
chains and traversed by a number of very remarkable parallel ridges. It
is situated nearly due N. of Plato on the N. edge of the Mare Frigoris,
and lies on the S.E. side of W.C. Bond, to which it bears a certain
resemblance. This region is characterised by the parallelism displayed by
many formations, large and small. It is more apparent hereabouts than in
any other part of the moon's visible surface. When favourably placed
under a low morning sun, Birmingham is a striking telescopic object.

FONTINELLE.--A fine ring-plain, 23 miles in diameter, on the N. margin of
the Mare Frigoris, N.N.E. of Plato, with a wall rising on the E., 6000
feet above a bright interior. I find its border indistinct and nebulous,
excepting under very oblique light, though three of the little craters
upon it are bright and prominent. One stands on the S., another on the
N.W., and a third on the E. Schmidt shows only the first of these, and
Neison none of them. Fontinelle has a low central mountain which is
easily distinguished. Fontinelle A, an isolated mountain on the S., is
more than 3000 feet high. On the N. there is a curious mountain group,
also of considerable altitude, and on the W. an irregular depression
surrounded by a dusky area. North of Fontinelle, extending towards
Goldschmidt and the limb, Schroter discovered a very wide irregular
valley which he named "J.J. Cassini." It is really nothing more than a
great plain bounded by ridges. At 9 h. October 15, 1888, when Philolaus
was on the morning terminator, I had a fine view of it, and, as regards
its general shape, found that it agreed very closely with Schroter's
drawing.

EPIGENES.--A remarkable ring-plain, about 26 miles in diameter, abutting
on a mountain ridge running parallel to the E. flank of W.C. Bond. It is
a notable object under a low morning sun. There are several elevations on
the floor.

GOLDSCHMIDT.--A great abnormally-shaped enclosure with lofty walls
between Epigenes and the limb. Neison mentions only two crater-pits
within. I have seen the rimmed crater shown by Schmidt on the W. side and
three or four other objects of a doubtful kind.

ANAXAGORAS.--A brilliant ring-plain of regular form, 32 miles in
diameter, adjoining Goldschmidt on the E. It is a prominent centre of
light streaks, some of which traverse the interior of Goldschmidt. On the
north a peak rises to the height of 10,000 feet. There is a long ridge on
the floor, running from E. to W.

GIOJA.--A ring-plain about 26 miles in diameter, near the north pole.

EAST LONGITUDE 20 deg. TO 40 deg.

REINHOLD.--A prominent ring-plain, 31 miles in diameter, with a lofty
border, rising at a peak on the W. to more than 9000 feet above the
floor. Its shape on the W. is clearly polygonal, the wall consisting of
three rectilineal sections, and on the E. it is made up of two straight
sections connected by a curved section. The inner slope includes a
remarkably distinct and regular terrace, the E. portion of which is well
seen when the interior is about half illuminated by the rising sun. At
this phase also the great extent of the _glacis_ on the S.W., and the
deep wide gullies traversing it on the E. are observed to the best
advantage. The central mountain, though of considerable size, is not
prominent. Close to Reinhold on the N.W. stands a noteworthy little
formation with a low and partially lineal wall, exhibiting a gap on the
north. There is a distinct crater on the S. side of its floor.

GAY-LUSSAC.--A very interesting ring-plain, 15 miles in diameter,
situated in the midst of the Carpathian Highlands N. of Copernicus, with
a smaller but brighter and deeper formation (Gay-Lussac A) on the S.W. of
it, and a conspicuous little crater, not more than 2 or 3 miles in
diameter, between the two. The interior of Gay-Lussac is traversed by two
coarse clefts, lying nearly in a meridional direction. The more easterly
runs from the foot of the S. wall, near the little crater just mentioned,
across the floor to the low N. border, which it apparently cuts through,
and extends for some distance beyond, terminating in a great oval
expansion. The other, which is not shown in the maps, is closely parallel
to it, and can be traced up to the N. border, but not farther. Schmidt
represents the first as a crater-row, which it probably is, as it varies
considerably in width. From the S.E. side of the formation extends a long
cleft, terminating at the end of a prominent spur from the S. side of the
Carpathians. There are also two remarkable rill-like valleys, commencing
on the N. of Gay-Lussac A, which curve round the W. side of Gay-Lussac.

HORTENSIUS.--This brilliant crater, about 10 miles in diameter, is
remarkable for its depth, and as being a ray-centre surrounded by a
nimbus of light. It has a central mountain, and Schmidt shows a minute
crater on the outer slope of the S. wall. The former is a test object.

MILICHIUS.--Is situated on the N.N.E. of Hortensius. It is fully as
bright, but rather smaller. Its floor, apparently devoid of detail, is
considerably depressed below the surrounding surface.

TOBIAS MAYER.--Like Gay-Lussac, a noteworthy ring-plain associated with
the Carpathian Mountains. It is 22 miles in diameter, and has a wall
which rises on the W. to a height of nearly 10,000 feet above the floor;
on the latter there is a conspicuous central mountain, and on the E. side
a crater, and some little hills. Schmidt shows a smaller crater on the W.
side, which I have not seen. Adjoining the formation on the W. is a ring-
plain of about one-fourth its area, which is a bright object. Tobias
Mayer and the neighbouring Carpathians form an especially beautiful
telescopic picture at sunrise.

KUNOWSKY.--An inconspicuous ring-plain, about 11 miles in diameter,
standing in a barren region in the Mare Procellarum, W.S.W. of Encke. The
central mountain is tolerably distinct.

ENCKE.--A regular ring-plain, 20 miles in diameter, with a comparatively
low border, nowhere rising more than 1800 feet above the interior, which
is depressed some 1000 feet below the surrounding Oceanus Procellarum. A
lofty ridge traverses the floor from S. to N., bifurcating before it
reaches the N. wall. There is a bright crater on the W. wall, and a
depression on the opposite wall, neither of which, strange to say, is
shown on the maps. Encke is encircled by ridges, which, when it is on the
morning terminator, combine to make it resemble a large crater surrounded
by a vast mountain ring.

KEPLER.--One of the most brilliant objects in the second quadrant,--a
ring-plain about 22 miles in diameter, with a lofty border; a peak on the
E. attaining an altitude of 10,000 feet above the surface. The wall is
much terraced, especially the outer slope on the W., where a narrow
valley is easily traceable. Though omitted from the maps, there is a
prominent circular depression on the W. border, which forms a distinct
notch thereon at sunrise. On the N., the wall exhibits a conspicuous
gap. There is a central hill on the floor. Immediately E. of Kepler is a
bright plateau, bounded on the N. by a very straight border, with two
small craters on its edge. Both these objects are incomplete on the N.,
as if they had been deformed by a "fault," which has apparently affected
the N. end of Kepler also. Kepler is the centre of one of the most
extended systems of bright streaks on the moon's visible surface.

BESSARION.--A bright little ring-plain, about 6 miles in diameter, in the
Oceanus Procellarum N. of Kepler. There is a smaller and still brighter
companion on the N. (Bessarion E), standing on a light area. Bessarion
has a minute central hill, difficult to detect.

PYTHEAS.--A small rhomboidal-shaped ring-plain, 12 miles in diameter,
standing in an isolated position on the Mare Imbrium between Lambert and
Gay-Lussac. Its bright walls, rising about 2500 feet above the Mare, are
much terraced within, especially on the E. There is a bright little
crater on the N. outer slope, with a short serpentine ridge running up to
it from the region S. of Lambert, and another winding ridge extending
from the S. wall to the E. of two conspicuous craters, standing about
midway between Pytheas and Gay-Lussac. The former bears a great
resemblance to the ridge N. of Madler, and, like this, appears to
traverse the N. border. The interior of Pytheas, which is depressed more
than 2000 feet below the Mare, includes a brilliant central peak.

LAMBERT.--A ring-plain, 17 miles in diameter, presenting many noteworthy
features. The crest of its border stands about 2000 feet above the Mare
Imbrium, and more than double this height above the interior. The wall is
prominently terraced both within and without; the outer slope on the W.
exhibiting at sunrise a nearly continuous valley running round it. When
near the morning terminator, the region on the N. is seen to be traversed
by some very remarkable ridges and markings; one cutting across the N.
wall appears to represent a "fault." On the S. is a large polygonal
enclosure formed by low ridges. On the W., towards Timocharis, is a
brilliant mountain 3000 feet high, a beautiful little object under a low
sun.

LEVERRIER.--The more westerly of a pair of little ring-plains on the N.
side of the Mare Imbrium, and S.W. of the Laplace promontory. It is about
10 miles in diameter, with walls rising some 1500 feet above the Mare,
and more than 6000 feet above the interior, which seems to be without a
central mountain or other features. Schmidt shows the crater on the N.
rim and another on the S.E. slope, both of which are omitted by Neison,
though they are easy objects when Helicon is on the morning terminator.
About 20 miles on the S.E. there is a very bright little crater on a
faint light area.

HELICON.--The companion ring-plain on the E. It is 13 miles in diameter,
and is very similar, though not quite so deep. There is a crater on the
S.E. wall, and, according to Neison, another on the outer slope of the N.
border. Webb records a central crater. If Helicon is observed when on the
morning terminator, it will be seen to be traversed by a curved ridge
which cuts through the walls, and runs up to a bright crater S.E. of
Leverrier. It appears to be a "fault," whose "downthrow," though slight,
is clearly indicated by an area of lower ground on the E. There is a
great number of small craters in the neighbourhood of this formation.

EULER.--The most easterly of the row of great ring-plains, which,
beginning on the W. with Autolycus, and followed by Archimedes,
Timocharis, and Lambert, extends almost in a great circle from the N.W.
to the S.E. side of the Mare Imbrium. It is about 19 miles in diameter,
and is surrounded by terraced walls, which, though of no great height
above the Mare, rise 6000 feet above the floor. There is a distinct
little gap in the S. wall, easily glimpsed when it is close to the
morning terminator, which probably represents a small crater. Euler has a
bright central mountain, and is a centre of white silvery streaks.

BRAYLEY.--A very conspicuous little ring-plain E.S.E. of Euler, with two
smaller but equally brilliant objects of the same class situated
respectively E. and W. of it.

DIOPHANTUS.--Forms with Delisle, its companion on the N., a noteworthy
object. It is about 13 miles in diameter, with a wall, which has a
distinct break in its continuity on the N., rising about 2500 feet above
the Mare. A rill-valley runs from the E. side of the ring towards the W.
face of a triangular-shaped mountain on the E. of a line joining the
formation with Delisle. North are three bright little craters in a line,
the middle one being much the largest. From the most easterly of these
objects a light streak may be traced under a high sun, extending for many
miles to another small crater on the N.W. of Diophantus, and expanding at
a point due N. of the formation into a spindle-shaped marking. At
sunrise, the W. portion of the streak has all the appearance of a cleft,
with a branch about midway running to the S. side of Delisle. Under the
same phase a broad band of shadow extends from the N.E. wall to the
triangular mountain just mentioned, representing a very sudden drop in
the surface--resembling on a small scale the well-known "railroad" E. of
Thebit. Diophantus has no central mountain.

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