The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1896-04-12


at Lick OF
craters properly so termed. According
to Mr.. Elger, the authority to whom
we have already referred. the most per-
feet example of a walled plain on the
moon is the great object known as
Ptolemaeus. The remarkable district so
designated covers AN area on our satel-
lite considerably larger than Wales. 1t
is situated nearly centrally on that
face of the moon directed towards US,
so that it generally lies very conven-
iently placed for examination. 1t will
be recognized as the last of a chain OF
four magnificent objects of the same
character which lie along the coast of
that darkest of lunar seas, known as
the Mare Nubium. Ptolemaeus may
be described as almost circular in out
line, though sometimes it might be re-
garded as a rudely six-sided figure. Its
appearance may be compared to that of
an eye-glass, whereof the little handle
is formed by a beautifully shaped
crater bearing the name of Herschel.
The floor of Ptolemaeus is a plain, not
much depressed below the general level
of the lunar surface. 1t is so vast that
an observer placed in it's midst would
see a boundless horizon stretching
away from him on all sides. He would
not realize the fact that PtoleamaeuSs
was surrounded, more or less complete
iy by noble circle of lofty mountains,
for these mountains would be below
his horizon. Some of the peaks ascend
one mile, and in certain cases even two
miles above the interior of the plain.
AT certain points the mountain chains
will be found interrupted by mighty
passes; especially is this the case on
the margin between Ptolemaeus and
the next adjoining walled plain, which
is called Alphonsus.
To my mind, however, the most inter-
esting of these objects, as we'll as per-
haps the most perfect representative
of its class, is the beautiful walled
plain named Plato. This is so well
placed, and has such a striking ap-
pearance that it is probably one of the
first objects which a student of lunar
topography succeeds in Identifying
No other object of the same character
happens to lie in it's neighborhood, and
consequently, there is but little diff
Guilty i'm distinguishing the walled plain
referred to. For it may be remarked
that the aspect of the moon changes
so frequently that Identification of
some features is at times a little
troublesome. This partly arises from
the never-endfng varieties OF light and
shade as the moon changes from day
to day.
There is also another circumstance
which Is sometimes apt to puzzle the
beginner, for. owing to what is called
the moons lbration, the face which is
directed towards us is not always eX-
actly the same. Hence it follows that
at different times the distance of OBJ
jects from the circular edge of the
moon to which they are lying nearest
will be found to vary. The difficulties,
will, however, not prevent the student
from readily identifying the superb OBJ
ject known as Plato. 1t lies in the
northern region of the moon, and as
our telescopes exhibit the object in
verified this means that Plato must be
sought at the lower part of the field
This walled plain is situated on the
coast line of a magnificent lunar sea,
namely, the Mare Imbrium, which may
! perhaps. be described as a stupendous
gulf branching off from the Oceanus
| Procellarum- This Is, indeed, the re-
gion of the moon towards which we
would specially direct the attention of
F, the student. There he will find mag
nificent examples of the most striking
| types of lunar scenery. The floor of
! Plato measures about sixty miles
across. It may be said TO be fiat, with
| the exception of certain small irregu-
|
strikes the attention of the observer,
and which is specially noticeable in the
photographs, is the unusual darkness
Of that floor as compared with other
parts Of the moon. The rampant of
| mountains which surround Plato are
comparatively perfect, and no more
pleasing lunar picture can be beheld
than when the shadows of these noun
tain peaks lie stretched along the dark
i
rs in such position that it would just
appear to be rising to lunar inhabit-
ant who was stationed in the neighbor-
hood.
HOW LUNAR MEASUREMENTS
ARE TAKEN.
7 NAV mention that the shadows of
lunar mountain peaks not only greatly
enhanse the beauty of our lunar pic
tllre from a spectacular point of view,
but they have another Importance.
They present to the astronomer the
only means which he possesses for
measuring the attitudes of the lunar
mountains. For, as lunar mountain
is more or less pointed towards the OBJ
server. it's elevation above the surface
cannot be obtained by direct measure
ments.
We may illustrate the process en-
ployed in the determination of the alti-
tude of a lunar mountain by the opera
ton of calculating the height of flag
staff from knowing the length of the
shadow which it casts at noon. If the
length of that shadow be measured on
certain days, which will, of course, vary
with the latitude of the observer, then
the length of the noon-tide shadow OF
the flagstaff would not be different
from the height of the flagstaff itself
Il the observations be made On any