CHAPTER VIII

DESCRIPTION OF CELESTIAL OBJECTS MENTIONED IN 'PARADISE LOST'


THE SUN

The surpassing splendour of the Sun, as compared with that of any of the
other orbs of the firmament, is not more impressive than his stupendous
magnitude, and the important functions which it is his prerogative to
fulfil. Situated at the centre of our system--of which he may be
regarded as 'both eye and soul'--the orb has a diameter approaching
1,000,000 miles, and a mass 750 times greater than that of all the
planets combined. These, by his attractive power, he retains in their
several paths and orbits, and even far distant Neptune acknowledges his
potent sway. With prodigal liberality he dispenses his vast stores of
light and heat, which illumine and vivify the worlds circling around
him, and upon the constant supply of which all animated beings depend
for their existence. Deprived of the light of the Sun, this world would
be enveloped in perpetual darkness, and we should all miserably perish.

The Sun is distant from the Earth about 93,000,000 miles. His diameter
is 867,000 miles, or nearly four times the extent of the radius of the
Moon's orbit. The mass of the orb exceeds that of the Earth 330,000
times, and in volume 1,305,000 times. The Sun is a sphere, and rotates
on his axis from west to east in 25 days 8 hours. The velocity of a
point at the solar equator is 4,407 miles an hour. The density of the
Sun is only one-fourth that of the Earth, or, in other words, bulk for
bulk, the Earth is four times heavier than the Sun. The force of gravity
at the Sun's surface is twenty-seven times greater than it is on the
Earth; it would therefore be impossible for beings constituted as we are
to exist on the solar surface.

The dazzling luminous envelope which indicates to the naked eye the
boundary of the solar disc is called the PHOTOSPHERE. It is most
brilliant at the centre of the Sun, and diminishes in brightness towards
the circumference, where its luminosity is but one-fourth that of the
central portion of the disc. The photosphere consists of gaseous vapours
or clouds, of irregular form and size, separated by less brilliant
interstices, and glowing white with the heat derived from the interior
of the Sun. In the telescope the photosphere is not of uniform
brilliancy, but presents a mottled or granular appearance, an effect
created by the intermixture of spaces of unequal brightness. Small
nodules of intense brilliance, resembling 'rice-grains,' but which,
according to Nasmyth, are of a willow-leaf shape with pointed
extremities, which form a network over portions of the photosphere, are
sprinkled profusely over a more faintly luminous background. These
'grains' consist of irregular rounded masses, having an area of several
hundred miles. By the application of a high magnifying power they can be
resolved into 'granules'--minute luminous dots which constitute
one-fifth of the Sun's surface and emit three-fourths of the light. This
granulation is not uniform over the surface of the photosphere; in some
parts it is indistinct, and appears to be replaced by interlacing
filamentous bands, which are most apparent in the penumbrae of the spots
and around the spots themselves. The 'granules' are the tops of
ascending masses of intensely luminous vapour; the comparatively dark
'pores' consist of similar descending masses, which, having radiated
their energy, are returning to be again heated underneath the surface of
the photosphere.

In certain regions of the photosphere several dark patches are usually
visible, which are called 'sun-spots.' At occasional times they are
almost entirely absent from the solar disc. It has been observed that
they occupy a zone extending from 10 deg. to 35 deg. north and south of the
solar equator, but are not found in the equatorial and polar regions of
the Sun. A sun-spot is usually described as consisting of an irregular
dark central portion, called the _umbra_; surrounding it is an edging or
fringe less dark, consisting of filaments radiating inwards called the
_penumbra_. Within the umbra there is sometimes seen a still darker
spot, called the _nucleus_. The umbra is generally uniformly dark, but
at times filmy luminous clouds have been observed floating over it. The
nucleus is believed to be the orifice of a tubular depression in the
floor of the umbra, prolonged downwards to an unknown depth. The
penumbra is brightest at its inner edge, where the filaments present a
marked contrast when compared with the dark cavity of the umbra which
they surround and overhang. Sometimes lengthened processes unite with
those of the opposite side and form bands and 'bridges' across the
umbra. The darkest portion of the penumbra is its external edge, which
stands out conspicuously against the adjoining bright surface of the
Sun. One penumbra will sometimes enclose several umbrae whilst the nuclei
may be entirely wanting.

[Illustration: FIG. 6.--A Sun-spot magnified.

(_Janssen._)]

Sun-spots usually appear in groups; large isolated spots are of rare
occurrence, and are generally accompanied by several smaller ones of
less perfect formation. The exact moment of the origin of a sun-spot
cannot be ascertained, because it arises from an imperceptible point; it
grows very rapidly, and often attains its full size in a day.

Prior to its appearance there is an unusual disturbance of the solar
surface over the site of the spot: luminous ridges, called _faculae_, and
dark 'pores' become conspicuous, between which greyish patches appear,
that seem to lie underneath a thin layer of the photosphere; this is
rapidly dispelled and a fully formed spot comes into view. When a
sun-spot has completed its period of existence, the photospheric matter
overwhelms the penumbra, and rushes into the umbra, which it
obliterates, causing the spot to disappear. The duration of sun-spots is
subject to considerable variation; some last for weeks or months, and
others for a few days or hours. A spot when once fully formed maintains
its shape, which is usually rounded, until the period of its breaking
up. Spots of long duration rotate with the Sun. Those which become
visible at the edge of the Sun's limb have been observed to travel
across his disc in less than a fortnight, disappearing at the margin of
the opposite limb; afterwards, if sufficiently long-lived, they have
reappeared in twelve or thirteen days on the surface of the orb where
first observed. It was by observation of the spots that the period of
the axial rotation of the Sun became known.

Sun-spots vary very much in size--some are only a few hundred miles in
width, whilst others have a diameter of 40,000 or 50,000 miles or
upwards. In some instances the umbra alone has a breadth of 20,000 or
30,000 miles--three times the extent of the diameter of the Earth. Spots
of this size are visible to the naked eye when the Sun is partially
obscured by fog, or when his brilliancy is diminished by vapours near
the horizon. A year seldom passes without the occurrence of several of
such spots being recorded. The largest sun-spot ever observed had a
diameter of about 150,000 miles. A group of spots, including their
penumbrae, will occupy an area of many millions of square miles.

By long observation it has been ascertained that sun-spots increase and
diminish in number with periodical regularity, and that a maximum
sun-spot period occurs at the end of each eleven years. When spots are
numerous on the Sun's disc there is great disturbance of the solar
surface, accompanied by fierce rushes of intensely heated gases. This
solar activity is known to influence terrestrial magnetism by causing a
marked oscillation of the magnetic needle, and giving rise to so-called
'magnetic storms,' accompanied by magnificent displays of aurorae, with
variations in electrical earth-currents. It would therefore appear that
sun-spots have a pronounced effect upon magnetic terrestrial phenomena,
but how this is produced remains unknown.

Besides sun-spots, there are seen on the solar disc bright flocculent
streaks or ridges of luminous matter called _faculae_; they are found
over the whole surface of the Sun, but are most numerous near the limb
and in the immediate vicinity of the spots. They have been compared to
immense waves--vast upheavals of photospheric matter, indicative of
enormous pressure, and often extending in length for many thousands of
miles.

Nearly all observers have arrived at the conclusion that sun-spots are
depressions or cavities in the photosphere, but considerable difference
of opinion exists as to how they are formed. The most commonly accepted
theory is that they are caused by the pressure of descending masses of
vapour having a reduced temperature, which absorb the light and prevent
it reaching us. Our knowledge of the Sun is insufficient to admit of any
accurate conclusion on this point; though we are able to perceive that
the surface of the orb is in a state of violent agitation and perpetual
change, yet his great distance and intense luminosity prevent our
capability of perceiving the ultimate minuter details which go to form
the _texture_ of the solar surface. 'Bearing in mind that a second of
arc on the Sun represents 455 miles, it follows that an object 150 miles
in diameter is about the _minimum visible_ even as a mere mathematical
point, and that anything that is sufficiently large to give the
slightest impression of shape and extension of surface must have an
area of at least a quarter of a million square miles; ordinarily
speaking, we shall not gather much information about any object that
covers less than a million.'[13] Since the British Islands have only an
area of 120,700 square miles, it is evident that on the surface of the
Sun there are many phenomena and physical changes occurring which escape
our observation. Though the changes which occur in the spots and faculae
appear to be slow when observed through the telescope, yet in reality
they are not so. Tremendous storms and cyclones of intensely heated
gases, which may be compared to the flames arising from a great furnace,
sweep over different areas of the Sun with a velocity of hundreds of
miles an hour. Vast ridges and crests of incandescent vapour are
upheaved by the action of internal heat, which exceeds in intensity the
temperature at which the most refractory of terrestrial substances can
be volatilised; and downrushes of the same photospheric matter take
place after it has parted with some of its stores of thermal energy.
Sun-spots of considerable magnitude have been observed to grow rapidly
and then disappear in a very short period of time; occasionally a spot
is seen to divide into two or more portions, the fragments flying
asunder with a velocity of not less than 1,000 miles an hour. It is by
these upheavals and convulsions of the solar atmosphere that the light
and heat are maintained which illumine and vivify the worlds that
gravitate round the Sun.

During total eclipses of the Sun, several phenomena become visible which
have enabled astronomers to gain some further knowledge of the nature of
the solar appendages. The most important of these is the CHROMOSPHERE,
which consists of layers of incandescent gases that envelop the
photosphere and completely surround the Sun. Its average depth is from
5,000 to 6,000 miles, and when seen during an eclipse is of a beautiful
rose colour, resembling a sheet of flame. As seen in profile at the edge
of the Sun's disc, it presents an irregular serrated appearance, an
effect created by the protuberance of luminous ridges and
processes--masses of flame which arise from over its entire surface. The
chromosphere consists chiefly of glowing hydrogen, and an element called
_helium_, which has been recently discovered in a terrestrial substance
called cleveite; there are also present the vapours of iron, calcium,
cerium, titanium, barium, and magnesium. From the surface of this ocean
of fire, jets and pointed spires of flaming hydrogen shoot up with
amazing velocity, and attain an altitude of ten, twenty, fifty, and even
one hundred thousand miles in a very short period of time. They are,
however, of an evanescent nature, change rapidly in form and appearance,
and often in the course of an hour or two die down so as not to be
recognisable. These _prominences_, as they are called, have been divided
into two classes. Some are in masses that float like clouds in the
atmosphere, which they resemble in form and appearance; they are
usually attached to the chromosphere by a single stem, or by slender
columns; occasionally they are entirely free. These are called
_quiescent_ prominences; they consist of clouds of hydrogen, and are of
more lasting duration than the other variety, called _eruptive_ or
metallic prominences. The latter are usually found in the vicinity of
sun-spots, and, besides hydrogen, contain the vapours of various metals.
They are of different forms, and present the appearance of filaments,
spikes, and jets of liquid fire; others are pyramidal, convoluted, and
parabolic.

These outbursts, bending over like the jets from a fountain, and
descending in graceful curves of flame, ascend from the surface of the
chromosphere with a velocity often exceeding 100 miles in a second, and
frequently reach an enormous height, but are of transient duration. They
are closely connected with sun-spots, and are evidence of the tremendous
forces that are in action on the surface of the Sun.

The CORONA is an aureole of light which is seen to surround the Sun
during a total eclipse. It is an impressive and beautiful phenomenon,
and is only visible when the Sun is concealed behind the dark body of
the Moon. Professor Young gives the following graphic description of the
corona: 'From behind it [the Moon] stream out on all sides radiant
filaments, beams, and sheets of pearly light, which reach to a distance
sometimes of several degrees from the solar surface, forming an
irregular stellate halo, with the black globe of the Moon in its
apparent centre. The portion nearest the Sun is of dazzling brightness,
but still less brilliant than the prominences, which blaze through it
like carbuncles. Generally this inner corona has a pretty uniform
height, forming a ring three or four minutes of arc in width, separated
by a somewhat definite outline from the outer corona, which reaches to a
much greater distance and is far more irregular in form. Usually there
are several "rifts," as they have been called, like narrow beams of
darkness, extending from the very edge of the Sun to the outer night,
and much resembling the cloud shadows which radiate from the Sun before
a thundershower. But the edges of these rifts are frequently curved,
showing them to be something else than real shadows. Sometimes there are
narrow bright streamers as long as the rifts, or longer. These are often
inclined, or occasionally even nearly tangential to the solar surface,
and frequently are curved. On the whole, the corona is usually less
extensive and brilliant over the solar poles, and there is a
recognisable tendency to accumulation above the middle latitudes, or
spot zones; so that, speaking roughly, the corona shows a disposition to
assume the form of a quadrilateral or four-rayed star, though in almost
every individual case this form is greatly modified by abnormal
streamers at some point or other.' The corona surrounds the Sun and its
other envelopes to a depth of many thousands of miles. It consists of
various elements which exist in a condition of extreme tenuity;
hydrogen, helium, and a substance called coronium appear to predominate,
whilst finely divided shining particles of matter and electrical
discharges resembling those of an aurora assist in its illumination.

[Illustration: FIG. 7.--The Corona during the Eclipse of May 1883.]

We possess no knowledge of the physical structure of the interior of the
Sun, nor have we any terrestrial analogy to guide us as to how matter
would behave when subjected to such conditions of extreme temperature
and pressure as exist in the interior of the orb. Yet we are justified
in concluding that the Sun is mainly a gaseous sphere which is slowly
contracting, and that the energy expended in this process is being
transformed into heat so extreme as to render the orb a great fountain
of light.

Milton in his poem makes more frequent allusion to the Sun than to any
of the other orbs of the firmament, and, in all his references to the
great luminary, describes him in a manner worthy of his unrivalled
splendour, and of his supreme importance in the system which he upholds
and governs. After having alighted on Mount Niphates, Satan is described
as looking

Sometimes towards Heaven and the full-blazing Sun,
Which now sat high in his meridian tower.--iv. 29-30.

He then addresses him thus:--

O thou that with surpassing glory crowned,
Look'st from thy sole dominion like the god
Of this new World--at whose sight all the stars
Hide their diminished heads--to thee I call,
But with no friendly voice, and add thy name,
O Sun, to tell thee how I hate thy beams,
That bring to my remembrance from what state
I fell, how glorious once above thy sphere.--iv. 32-39.

On another occasion:--

The golden Sun in splendour likest Heaven
Allured his eye.--iii. 572-73.

In describing the different periods of the day, Milton seldom fails to
associate the Sun with these times, and rightly so, since they are
brought about by the apparent diurnal journey of the orb across the
heavens. Commencing with morning, he says:--

Meanwhile,
To re-salute the world with sacred light,
Leucothea waked, and with fresh dews embalmed
The Earth.--xi. 133-36.

Soon as they forth were come to open sight
Of day-spring, and the Sun--who, scarce up-risen,
With wheels yet hovering o'er the ocean-brim,
Shot parallel to the Earth his dewy ray,
Discovering in wide landskip all the east
Of Paradise and Eden's happy plains.--v. 138-43

or some renowned metropolis
With glistering spires and pinnacles adorned,
Which now the rising Sun gilds with his beams.--iii. 549-51.

while now the mounted Sun
Shot down direct his fervid rays, to warm
Earth's inmost womb.--v. 300-302.

for scarce the Sun
Hath finished half his journey, and scarce begins
His other half in the great zone of Heaven.--v. 558-60.

To sit and taste, till this meridian heat
Be over, and the Sun more cool decline.--v. 369-70.

And the great Light of Day yet wants to run
Much of his race, though steep. Suspense in Heaven,
Held by thy voice, thy potent voice he hears,
And longer will delay, to hear thee tell
His generation, and the rising birth
Of Nature from the unapparent deep.--vii. 98-103.

The declining day and approach of evening are described as follows:--

Meanwhile in utmost longitude, where Heaven
With Earth and Ocean meets, the setting Sun
Slowly descended, and with right aspect
Against the eastern gate of Paradise
Levelled his evening rays.--iv. 539-43.

the Sun now fallen
Beneath the Azores; whether the Prime Orb,
Incredible how swift, had thither rolled
Diurnal, or this less volubil Earth,
By shorter flight to the east, had left him there
Arraying with reflected purple and gold
The clouds that on his western throne attend.--iv. 591-97.

the parting Sun
Beyond the Earth's green Cape and verdant Isles
Hesperian sets, my signal to depart.--viii. 630-32.

Now was the Sun in western cadence low
From noon, and gentle airs due at their hour
To fan the Earth now waked, and usher in
The evening cool.--x. 92-95.

for the Sun,
Declined, was hasting now with prone career
To the Ocean Isles, and in the ascending scale
Of Heaven the stars that usher evening rose.--iv. 352-55.

In the combat between Michael and Satan, which ended in the overthrow of
the rebel angels, Milton, in his description of their armour, says:--

two broad suns their shields
Blazed opposite.--vi. 305-306,

and in describing the faded splendour of the ruined Archangel, the poet
compares him to the Sun when seen under conditions which temporarily
deprive him of his dazzling brilliancy and glory:--

as when the Sun new-risen
Looks through the horizontal misty air
Shorn of his beams, or, from behind the Moon
In dim eclipse, disastrous twilight sheds
On half the nations, and with fear of change
Perplexes monarchs.--i. 594-99.

This passage affords us an example of the sublimity of Milton's
imagination and of his skill in adapting the grandest phenomena in
Nature to the illustration of his subject.


THE MOON

The Moon is the Earth's satellite, and next to the Sun is the most
important of the celestial orbs so far as its relations with our globe
are concerned. Besides affording us light by night, the Moon is the
principal cause of the ebb and flow of the tide--a phenomenon of much
importance to navigators. The Moon is almost a perfect sphere, and is
2,160 miles in diameter. The form of its orbit is that of an ellipse
with the Earth in the lower focus. It revolves round its primary in 27
days 7 hours, at a mean distance of 237,000 miles, and with a velocity
of 2,273 miles an hour. Its equatorial velocity of rotation is 10 miles
an hour. The density of the Moon is 3.57 that of water, or 0.63 that of
the Earth; eighty globes, each of the weight of the Moon, would be
required to counterbalance the weight of the Earth, and fifty globes of
a similar size to equal it in dimensions. The orb rotates on its axis in
the same period of time in which it accomplishes a revolution of its
orbit; consequently the same illumined surface of the Moon is always
directed towards the Earth. To the naked eye the Moon appears as large
as the Sun, and it very rapidly changes its form and position in the
sky. Its motions, which are of a very complex character, have been for
many ages the subject of investigation by mathematicians and
astronomers, but their difficulties may now be regarded as having been
finally overcome.

The phases of the Moon are always interesting and very beautiful. The
orb is first seen in the west, after sunset, as a delicate slender
crescent of pale light; each night it increases in size, whilst it
travels eastward, until it attains the figure of a half moon; still
growing larger as it pursues its course, it finally becomes a full
resplendent globe, rising about the time that the Sun sets and situated
directly opposite to him. Then, in a reverse manner, after full moon, it
goes through the same phases, until, as a slender crescent, it becomes
invisible in the solar rays; afterwards to re-appear in a few days, and,
in its monthly round, to undergo the same cycle of changes. The phases
of the Moon depend upon the changing position of the orb with regard to
the Sun. The Moon shines by reflected light derived from the Sun, and as
one half of its surface is always illumined and the other half totally
dark, the crescent increases or diminishes when, by the Moon's change of
position, we see more or less of the bright side. Visible at first as a
slender crescent near the setting Sun, the angular distance from the orb
and the width of the crescent increase daily, until, at the expiration
of seven days, the Moon is distant one quarter of the circumference of
the heavens from the Sun. The Moon is then a semi-circle, or in
quadrature. At the end of other seven days, the distance of the Moon
from the Sun is at its greatest--half the circumference of its orbit. It
is then visible as a circular disc and we behold the orb as full moon.
The waning Moon, as it gradually decreases, presents the same aspects
reversed, and, finally, its slender crescent disappears in the Sun's
rays. The convex edge of the crescent is always turned towards the Sun.
The rising of the Moon in the east and its setting in the west is an
effect due to the diurnal rotation of the Earth on her axis, but the orb
can be perceived to have two motions besides: one from west to east,
which carries it round the heavens in 29.53 days, and another from north
to south. The west to east motion is steady and continuous, but, owing
to the Sun's attractive force, the Moon is made to swerve from its path,
giving rise to irregularities of its motion called PERTURBATIONS. The
most important of these is the _annual equation_, discovered by Tycho
Brahe--a yearly effect produced by the Sun's disturbing influence as the
Earth approaches or recedes from him in her orbit; another irregularity,
called the _evection_, is a change in the eccentricity of the lunar
orbit, by which the mean longitude of the Moon is increased or
diminished. _Elliptic inequality_, _parallactic inequality_, the
_variation_, and _secular acceleration_, are other perturbations of the
lunar motion, which depend directly or indirectly on the attractive
influence of the Sun and the motion of the Earth in her orbit.

As the plane of the Moon's orbit is inclined at an angle of rather more
than 5 deg. to the ecliptic, it follows that the orb, in its journey round
the Earth, intersects this great circle at two points called the
'Nodes.' When crossing the ecliptic from south to north the Moon is in
its ascending node, and when crossing from north to south in its
descending node. In December the Moon reaches the most northern point of
its course, and in June the southernmost. Consequently we have during
the winter nights the greatest amount of moonlight, and in summer the
least. In the evenings the moonlight is least in March and greatest in
September, when we have what is called the Harvest Moon.

The telescopic appearance of the Moon is very interesting and beautiful,
especially if the orb is observed when waxing and waning. As no aqueous
vapour or cloud obscures the lunar surface, all its details can be
perceived with great clearness and distinctness. Indeed, the topography
of the Moon is better known than that of the Earth, for the whole of its
surface has been mapped and delineated with great accuracy and
precision. The Moon is in no sense a duplicate of its primary, and no
analogy exists between the Earth and her satellite. Evidence is wanting
of the existence of an atmosphere surrounding the Moon; no clouds or
exhalations can be perceived, and no water is believed to exist on the
lunar surface. Consequently there are no oceans, seas, rivers, or lakes;
no fertile plains or forest-clad mountains, such as are found upon the
Earth. Indeed, all the conditions essential for the support and
maintenance of organic life by which we are surrounded appear to be
nonexistent on the Moon. Our satellite has no seasons; its axial
rotation is so slow that one lunar day is equal in length to fourteen of
our days; this period of sunshine is succeeded by a night of similar
duration. The alternation of such lengthened days and nights subjects
the lunar surface to great extremes of heat and cold.

When viewed with a telescope, the surface of the Moon is perceived to
consist of lofty mountain chains with rugged peaks, numerous extinct
volcanoes called crater mountains, hills, clefts, chasms, valleys, and
level plains--a region of desolation, presenting to our gaze the
shattered and upturned fragments of the Moon's crust, convulsed by
forces of a volcanic nature which have long since expended their
energies and died out. The mountain ranges on the Moon resemble those of
the Earth, but they have a more rugged outline, and their peaks are more
precipitous, some of them rising to a height of 20,000 feet. They are
called the Lunar Alps, Apennines, and Cordilleras, and embrace every
variety of hill, cliff, mound, and ridge of comparatively low
elevation. The plains are large level areas, which are situated on
various parts of the lunar surface; they are of a darker hue than the
mountainous regions by which they are surrounded, and were at one time
believed to be seas. They are analogous to the prairies, steppes, and
deserts of the Earth.

_Valleys._--Some of these are of spacious dimensions; others are narrow,
and contract into gorges and chasms. Clefts or rills are long cracks or
fissures of considerable depth, which extend sometimes for hundreds of
miles across the various strata of which the Moon's crust is composed.

The characteristic features of the Moon's surface are the crater
mountains: they are very numerous on certain portions of the lunar disc,
and give the Moon the freckled appearance which it presents in the
telescope, and which Galileo likened to the eyes in the feathers of a
peacock's tail. They are believed to be of volcanic origin, and have
been classified as follows: 'Walled plains, mountain rings, ring plains,
crater plains, craters, craterlets, and crater cones.' Upwards of 13,000
of these mountains have been enumerated, and 1,000 are known to have a
diameter exceeding nine miles. Walled plains consist of circular areas
which have a width varying from 150 miles to a few hundred yards. They
are enclosed by rocky ramparts, whilst the centre is occupied by an
elevated peak. The depth of these formations, which are often far below
the level of the Moon's surface, ranges from 10,000 to 20,000 feet.
Mountain rings, ring plains, and crater plains resemble those already
described, but are on a smaller scale; the floors of the larger ones are
frequently occupied by craters and craterlets. The latter exist in large
numbers, and some portions of the Moon's surface appear honeycombed with
them, the smaller craters resting on the sides of larger ones and
occupying the bottoms of the more extensive areas. There is no kind of
formation on the Earth's surface that can be compared with these crater
mountains, which indicate that the Moon was at one time a fiery globe
convulsed by internal forces which found an outlet in the numerous
volcanoes scattered over her surface.

The most remarkable of these volcanic mountains have been named after
distinguished men. (1) Copernicus is one of the most imposing; its
crater is 56 miles in diameter, and situated at its centre is a mountain
with six peaks 2,400 feet in height. The ring by which it is surrounded
rises 11,000 feet above the floor of the crater, and consists of
terraces believed to have been created by the partial congelation and
periodic subsidence of a lake of molten lava which occupied the enclosed
area.

(2) Tycho is one of the most magnificent and perfect of lunar volcanoes,
and is also remarkable as being a centre from which, when the Moon is
full, there radiates a number of bright streaks which extend across the
lunar surface, over mountain and valley, through ring and crater, for
many hundreds of miles. Their nature is unknown, and nothing resembling
them is found on the Earth. Tycho has a diameter of 50 miles and a
depth of 17,000 feet. The peak which rises from the floor of the crater
attains a height of 6,000 feet, and the rampart consists of a series of
terraces which give variety to the appearance of the inner wall. The
surface of the Moon round Tycho is honeycombed with small volcanoes.

(3) Clavius is one of the most extensive of the walled plains; it has a
diameter of 142 miles and an area of 16,500 square miles. The rocky
annulus which surrounds it is very lofty and precipitous, and at one
point reaches a height of 17,300 feet. Upwards of 90 craters have been
counted within this space, one of the peaks attaining to an elevation of
24,000 feet above the level floor of the plain. It is believed that the
lowest depths of this wild and precipitous region are never penetrated
by sunlight, they are so overshadowed by towering crag and fell which
intercept the solar rays; and, as there is no atmosphere to cause
reflection, they are consequently enveloped in perpetual darkness.

(4) Plato has a diameter of about 60 miles and an area of 2,700 square
miles; its central peak rises to a height of 7,300 feet. It has an
irregular rampart which is broken up into terraces averaging about 4,000
feet high; three cones, each with an elevation of from 7,000 to 9,000
feet, rest on its western border.

(5) Theophilus is the deepest of the visible craters on the Moon. It has
a diameter of 64 miles, and the inner edge of the ring rises from the
level floor to a height ranging from 14,000 to 18,000 feet. A group of
mountains occupies the centre of the area, the highest peak of which
reaches an elevation of 5,200 feet. Cyrillus and Catharina, two adjacent
craters, are each about 16,000 feet deep and connected by a wide valley.

(6) Aristarchus is the brightest spot on the Moon, and appears almost
dazzling in the telescope. The crater has a diameter of 42 miles, the
centre of which is occupied by a steep mountain. The rampart on the
western side rises to a height of 7,500 feet, on the east it becomes a
plateau which connects it with a smaller crater called Herodotus. Bright
streaks radiate from Aristarchus when there is full moon, and extend for
a considerable distance over the surface of the orb.

Though the face of the Moon has been carefully scanned for two centuries
and a half, and selenographers have mapped and delineated her features
with the utmost accuracy and precision, yet no perceptible change of a
reliable character has been perceived to occur on any part of the orb.
The surface of the hemisphere directed towards the Earth appears to be
an alternation of desert plains, craggy wildernesses, and extinct
volcanoes--a region of desolation unoccupied by any living thing, and
'upon which the light of life has never dawned.' Owing to the absence of
an atmosphere, there is neither diffuse daylight nor twilight on the
Moon. Every portion of the lunar surface not exposed to the Sun's rays
is shrouded in darkness, and black shadows can be observed fringing
prominences of silvery whiteness. If the Moon were enveloped in an
atmosphere similar to that which surrounds the Earth, the reflection and
diffusion of light among the minute particles of watery vapour which
permeate it would give rise to a gradual transition from light to
darkness; the lunar surface would be visible when not illumined by the
direct rays of the Sun, and before sunrise and after sunset, dawn and
twilight would occur as upon the Earth. But upon the Moon there is no
dawn, and the darkness of night envelops the orb until the appearance of
the edge of the Sun's disc above the horizon, then his dazzling rays
illumine the summits and loftiest peaks of the lunar mountains whilst
yet their sides and bases are wrapped in deep gloom. Since the pace of
the Sun across the lunar heavens is 28 times slower than it is with us,
there is continuous sunshine on the Moon for 304 hours, and this long
day--equal to about a fortnight of our time--is succeeded by a night of
similar duration. As there is no atmosphere overhead to diffuse or
reflect the light, the Sun shines in a pitch-black sky, and at lunar
noonday the planets and constellations can be seen displaying a
brilliancy of greater intensity than can be perceived on Earth during
the darkest night. Every portion of the Moon's surface is bleak, bare,
and untouched by any softening influences. No gentle gale ever sweeps
down her valleys or disturbs the dead calm that hangs over this world;
no cloud ever tempers the fierce glare of the Sun that pours down his
unmitigated rays from a sky of inky blackness; no refreshing shower ever
falls upon her arid mountains and plains; no sound ever breaks the
profound stillness that reigns over this realm of solitude and
desolation.

[Illustration: A PORTION OF THE MOON'S SURFACE]

As might be expected, Milton makes frequent allusion to the Moon in
'Paradise Lost,' and does not fail to set forth the distinctive charms
associated with the unrivalled queen of the firmament. The majority of
poets would most likely regard a description of evening as incomplete
without an allusion to the Moon. Milton has adhered to this sentiment,
as may be perceived in the following lines:--

till the Moon,
Rising in clouded majesty, at length
Apparent queen, unveiled her peerless light,
And o'er the dark her silver mantle threw.--iv. 606-609.

now reigns
Full-orbed the Moon, and with more pleasing light,
Shadowy sets off the face of things.--v. 41-43.

The association of the Moon with the nocturnal revels and dances of
elves and fairies is felicitously expressed in the following passage:--

or faery elves,
Whose midnight revels, by a forest side
Or fountain, some belated peasant sees,
Or dreams he sees, while overhead the Moon
Sits arbitress, and nearer to the Earth
Wheels her pale course.--i. 781-86.

In contrast with this, we have Milton's description of the Moon when
affected by the demoniacal practices of the 'night-hag' who was believed
to destroy infants for the sake of drinking their blood, and applying
their mangled limbs to the purposes of incantation. The legend is of
Scandinavian origin and the locality Lapland:--

Nor uglier follow the night-hag, when called
In secret, riding through the air she comes,
Lured with the smell of infant blood, to dance
With Lapland witches, while the labouring Moon
Eclipses at their charms.--ii. 662-66.

In his description of the massive shield carried by Satan, the poet
compares it with the full moon:--

his ponderous shield
Ethereal temper, massy, large, and round,
Behind him cast. The broad circumference
Hung on his shoulders like the Moon.--i. 284-87.

The phases displayed by the Moon in her monthly journey round the Earth,
and which lend a variety of charm to the appearances presented by the
orb, are poetically described by Milton in the following lines:--

but there the neighbouring Moon
(So call that opposite fair star) her aid
Timely interposes, and her monthly round
Still ending, still renewing, through mid-Heaven
With borrowed light her countenance triform
Hence fills and empties, to enlighten the Earth,
And in her pale dominion checks the night.--iii. 726-32.

It is interesting to observe how aptly Milton describes the subdued
illumination of the Moon's reflected light, as compared with the
brilliant radiance of the blazing Sun, and how the distinguishing glory
peculiar to each orb is appropriately set forth in the various passages
in which they are described; their contrasted splendour enhancing rather
than detracting from the grandeur and beauty belonging to each.


THE PLANET EARTH[14]

No lovelier planet circles round the Sun than the planet Earth, with her
oceans and continents, her mountains, valleys, rivers, lakes, and
plains; surrounded by heaven's azure, radiant with the sunlight of her
day and adorned by night with countless sparkling points of gold. This
beautiful world, the abode of MAN, is of paramount importance to us, and
is the only part of the universe of which we have any direct knowledge.

The Earth may be regarded as one of the Sun's numerous family, and is
situated third in order from the refulgent orb, round which it revolves
in an elliptical orbit at a mean distance of 92,800,000 miles. The Earth
is nearest to the Sun at the end of December, and furthest away at the
beginning of July; the difference between those distances is 3,250,000
miles--the extent of the eccentricity of the planet's orbit. The figure
of the Earth is that of an oblate spheroid; it is slightly flattened at
the poles and bulges at the equator. Its polar or shortest diameter is
7,899 miles, its equatorial diameter is 7,926 miles--greater than the
other by 27 miles. The circumference of the Earth at the equator is
24,899 miles, and the total area of its surface is 197,000,000 square
miles. Its mean density is 5-1/2 times greater than that of water.

The two principal motions performed by the Earth are: (1) Rotation on
its axis; (2) its annual revolution round the Sun. The Earth always
rotates in the same manner, and in the same direction, from west to
east. As the axis of rotation corresponds with the shortest diameter of
the planet, it affords strong evidence that the Earth assumed its
present shape whilst rapidly rotating round its axis when in a fluid or
plastic condition. This would accord with the nebular hypothesis. The
ends of the Earth's axis are called the poles of the Earth; one is the
north, the other the south pole. The north pole is directed towards a
star in the Lesser Bear called the Pole Star. The south pole is directed
to a corresponding opposite part of the heavens. The Earth's axis is
inclined 63 deg. 33' to the plane of the ecliptic, and is always directed to
the same point in the heavens. The Earth accomplishes a revolution on
its axis in 23 hours 56 minutes 4 seconds mean solar time, which is the
length of the sidereal day. This rate of rotation is invariable. At the
equator, where the circumference of the globe exceeds 24,000 miles, the
velocity of a point on its surface is upwards of 1,000 miles an hour,
but, as the poles are approached, the tangential velocity diminishes,
and at those points it is entirely absent. The Earth accomplishes a
revolution of her orbit in 365 days 6 hours 9 minutes; in her journey
round the Sun she travels a circuit of 580,000,000 miles at an average
pace of 66,000 miles an hour. The Earth has other slight motions called
_perturbations_, which are produced by the gravitational attraction of
other members of the solar system. The most important of these is
Precession of the Equinoxes, which is caused by the attraction of the
Sun, Moon, and planets, on the protuberant equatorial region of the
globe. This attraction has a tendency to turn the Earth's axis at right
angles to her orbit, but it only results in the slow rotation of the
pole of the equator round that of the ecliptic, which is occurring at
the rate of 1 deg. in 70 years, and will require a period of 25,868 years to
complete an entire revolution of the heavens.

The spot on Earth round which is centred the chief interest in Milton's
poem is Paradise, which was situated in the east of Eden, a district of
Central Asia. It was here where God ordained that man should first
dwell--a place created for his enjoyment and delight. Satan, after his
soliloquy on Mount Niphates, directs his way to Paradise, and arrives
first in Eden, where he beholds from a distance the Happy Garden--

So on he fares, and to the border comes
Of Eden, where delicious Paradise,
Now nearer, crowns with her enclosure green,
As with a rural mound, the champain head
Of a steep wilderness, whose hairy sides
With thicket overgrown, grotesque and wild,
Access denied; and overhead upgrew
Insuperable highth of loftiest shade,
Cedar, and pine, and fir, and branching palm,
A sylvan scene, and, as the ranks ascend,
Shade above shade, a woody theatre
Of stateliest view. Yet higher than their tops
The verdurous wall of Paradise up-sprung;
Which to our general sire gave prospect large
Into his nether empire neighbouring round.
And higher than that wall, a circling row
Of goodliest trees, loaden with fairest fruit,
Blossoms and fruits at once of golden hue,
Appeared, with gay enamelled colours mixed;
On which the Sun more glad impressed his beams
Than in fair evening cloud, or humid bow,
When God hath showered the Earth: so lovely seemed
That landskip. And of pure now purer air
Meets his approach, and to the heart inspires
Vernal delight and joy, able to drive
All sadness but despair. Now gentle gales,
Fanning their odoriferous wings, dispense
Native perfumes, and whisper whence they stole
Those balmy spoils.--iv. 131-59.

Satan, having gained admission to the Garden by overleaping the tangled
thicket of shrubs and bushes which formed an impenetrable barrier and
prevented any access to the enclosure within, he flew up on to the Tree
of Life--

Beneath him, with new wonder, now he views,
To all delight of human sense exposed,
In narrow room Nature's whole wealth; yea, more!--
A Heaven on Earth: for blissful Paradise
Of God the garden was, by Him in the east
Of Eden planted, Eden stretched her line
From Auran eastward to the royal towers
Of great Seleucia, built by Grecian kings,
Or where the sons of Eden long before
Dwelt in Telassar. In this pleasant soil
His far more pleasant garden God ordained.
Out of the fertile ground he caused to grow
All trees of noblest kind for sight, smell, taste;
And all amid them stood the Tree of Life,
High eminent, blooming ambrosial fruit
Of vegetable gold; and next to life,
Our death, the Tree of Knowledge, grew fast by--
Knowledge of good, bought dear by knowing ill.
Southward through Eden went a river large,
Nor changed his course, but through the shaggy hill
Passed underneath ingulfed; for God had thrown
That mountain, as his garden mould, high raised
Upon the rapid current, which, through veins
Of porous earth with kindly thirst up-drawn,
Rose a fresh fountain, and with many a rill
Watered the garden; thence united fell
Down the steep glade, and met the nether flood,
Which from his darksome passage now appears,
And now, divided into four main streams,
Runs diverse, wandering many a famous realm
And country whereof here needs no account;
But rather to tell how, if Art could tell
How, from that sapphire fount the crisped brooks,
Boiling on orient-pearl and sands of gold,
With mazy error under pendent shades
Ran nectar, visiting each plant, and fed
Flowers worthy of Paradise, which not nice Art
In beds and curious knots, but Nature boon
Poured forth profuse on hill, and dale, and plain,
Both where the morning Sun first warmly smote
The open field, and where the unpierced shade
Imbrowned the noontide bowers.--iv. 205-46.

Milton's description of Paradise is not less remarkable in its way than
the lurid scenes depicted by him in Pandemonium. The versatility of his
poetic genius is nowhere more apparent than in the charming pastoral
verse contained in this part of his poem. The poet has lavished the
whole wealth of his luxuriant imagination in his description of Eden and
blissful Paradise with its 'vernal airs' and 'gentle gales,' its verdant
meads, and murmuring streams, 'rolling on orient-pearl and sands of
gold;' its stately trees laden with blossom and fruit; its spicy groves
and shady bowers, over which there breathed the eternal Spring.

In Book IX. Satan expresses himself in an eloquent apostrophe to the
primitive Earth, over which he previously wandered for seven days--

O Earth, how like to Heaven, if not preferred
More justly, seat worthier of gods, as built
With second thoughts, reforming what was old!
For what God, after better, worse would build?
Terrestrial Heaven, danced round by other Heavens,
That shine, yet bear their bright officious lamps,
Light above light, for thee alone, as seems,
In thee concentring all their precious beams
Of sacred influence! As God in Heaven
Is centre, yet extends to all, so thou
Centring receiv'st from all those orbs; in thee,
Not in themselves, all their known virtue appears,
Productive in herb, plant, and nobler birth
Of creatures animate with gradual life
Of growth, sense, reason, all summed up in Man,
With what delight I could have walked thee round,
If I could joy in aught--sweet interchange
Of hill and valley, rivers, woods, and plains,
Now land, now sea, and shores with forest crowned,
Rocks, dens, and caves.--ix. 99-118.

Though it is impossible to regard the Earth as possessing the importance
ascribed to it by the ancient Ptolemaists; nevertheless, our globe is a
great and mighty world, and appears to be one of the most favourably
situated of all the planets, being neither near the Sun nor yet very far
distant from the orb; and although, when compared with the universe, it
is no more than a leaf on a tree in the midst of a vast forest; still,
it is not the least important among other circling worlds, and
unfailingly fulfils the part allotted to it in the great scheme of
creation.


THE PLANET HESPERUS

This is the beautiful morning and evening star, the peerless planet that
ushers in the twilight and the dawn, the harbinger of day and unrivalled
queen of the evening. Venus, called after the Roman goddess of Love, and
also identified with the Greek Aphrodite of ideal beauty, is the name by
which the planet is popularly known; but Milton does not so designate
it, and the name 'Venus' is not found in 'Paradise Lost.' The ancients
called it Lucifer and Phosphor when it shone as a morning star before
sunrise, and Hesperus and Vesper when it became visible after sunset. It
is the most lustrous of all the planets, and at times its brilliancy is
so marked as to throw a distinct shadow at night.

Venus is the second planet in order from the Sun. Its orbit lies between
that of Mercury and the Earth, and in form approaches nearer to a circle
than that of any of the other planets. It travels round the Sun in
224.7 days, at a mean distance of 67,000,000 miles, and with an average
velocity of 80,000 miles an hour. Its period of rotation is unknown. By
the observation of dusky spots on its surface, it has been surmised that
the planet completes a revolution on its axis in 23-1/4 hours; but other
observers doubt this and are inclined to believe that it always presents
the same face to the Sun. When at inferior conjunction Venus approaches
nearer to the Earth than any other planet, its distance then being
27,000,000 miles. Its greatest elongation varies from 45 deg. to 47 deg. 12'; it
therefore can never be much more than three hours above the horizon
before sunrise, or after sunset. Venus is a morning star when passing
from inferior to superior conjunction, and during the other half of its
synodical period it is an evening star. The planet attains its greatest
brilliancy at an elongation 40 deg. west or east of the Sun--five weeks
before and after inferior conjunction. It is at these periods, when at
its greatest brilliancy, that it casts a shadow at night.

Though so pleasing an object to the unaided eye, Venus, when observed
with the telescope, is often a source of disappointment--this is on
account of its dazzling brilliancy, which renders any accurate
definition of its surface impossible. Sir John Herschel writes: 'The
intense lustre of its illuminated part dazzles the sight, and
exaggerates every imperfection of the telescope; yet we see clearly that
its surface is not mottled over with permanent spots like the Moon; we
notice in it neither mountains nor shadows, but a uniform brightness, in
which sometimes we may indeed fancy, or perhaps more than fancy,
brighter or obscurer portions, but can seldom or never rest fully
satisfied of the fact.' It is believed that the surface of the planet is
invisible on account of the existence of a cloud-laden atmosphere by
which it is enveloped, and which may serve as a protection against the
intense glare of the sunshine and heat poured down by the not
far-distant Sun. Schroeter, a German astronomer, believed that he saw
lofty mountains on the surface of the planet, but their existence has
not been confirmed by any other observer. The Sun if viewed from Venus
would have a diameter nearly half as large again as when seen from the
Earth; it is therefore probable that the planet is subjected to a much
higher temperature than what is experienced on our globe.

The phases of Venus are similar to those exhibited by the Moon, and are
caused by a change in position of the illumined hemisphere of the planet
with regard to the Earth. At superior conjunction the whole enlightened
disc of the planet is turned towards the Earth, but is invisible by
being lost in the Sun's rays. Shortly before or after it arrives at this
point, its form is gibbous, the illumined portion being less than a
circle but greater than a semi-circle. At its greatest elongation west
or east of the Sun the planet resembles the Moon in quadrature--a half
moon--and between those points and inferior conjunction it is visible
as a beautiful crescent. It becomes narrower and sharper as it
approaches inferior conjunction, until it resembles a curved luminous
thread prior to its disappearance at the conjunction. After having
passed this point it reappears on the other side of the Sun as the
morning star.

It would be only natural to imagine that this peerless orb, the most
beautiful and lustrous of the planets, upon which men have gazed with
longing admiration, and designated the emblem of 'all beauty and all
love,' should have impressed Milton's poetical imagination with its
charming appearance, and stimulated the flow of his captivating muse. He
addresses the orb as

Fairest of Stars, last in the train of night,
If better thou belong not to the dawn,
Sure pledge of day, that crown'st the smiling morn
With thy bright circlet, praise Him in thy sphere
While day arises, that sweet hour of prime.--v. 166-70.

In these lines the poet alludes to Venus as the morning star.

In the other passages in his poem Milton associates the planet sometimes
with the morning and at other times with the evening--

His countenance, as the Morning Star that guides
The starry flock.--v. 708-709.

Or if the Star of Evening and the Moon
Haste to thy audience, Night with her will bring
Silence, and Sleep listening to thee will watch.--vii. 104-106.

And hence the morning planet gilds her horns.--vii. 366.

The Sun was sunk and after him the Star
Of Hesperus, whose office is to bring
Twilight upon the Earth, short arbiter
Twixt day and night.--ix. 47-50.

and bid haste the Evening Star
On his hill top to light the bridal lamp.--viii. 519-20.

Milton knew of the phases of Venus and was aware that at certain times
the planet was visible in the telescope as a beautiful crescent. The
line in which he mentions her as gilding her horns is an allusion to
this appearance of Venus.


THE PLEIADES

The beautiful cluster of the Pleiades or Seven Sisters has been regarded
with hallowed veneration from time immemorial. The happy influences
believed to be shed down upon the Earth by those stars and their close
association with human destinies have rendered them objects of almost
sacred interest among the different races of mankind. In every region of
the globe and in every clime, among civilised nations and savage
fetish-worshipping tribes, the same benign influences were ascribed to
the stars which form this interesting group.

In Greek mythology they were known as the seven daughters of Atlas and
Pleione. Different versions are given of their fate. By some writers it
is said they died from grief in consequence of the death of their
sisters, the Hyades, or on account of the fate of their father, who,
for treason, was condemned by Zeus to bear on his head and hands the
vault of heaven, on the mountains of north-west Africa which bear his
name. According to others they were the companions of Diana, and, in
order to escape from Orion, by whom they were pursued, the gods
translated them to the sky.

All writers agree in saying that after their death or translation they
were transformed into stars. Their names are Alcyone, Electra, Maia,
Merope, Sterope, Taygeta, and Celaeno. The seventh Atlantid is said to
be the 'lost Pleiad,' but it can be perceived without difficulty by a
person possessing good eyesight. In the book of Job there is a beautiful
allusion to the Pleiades (chap. xxxviii.) when God speaks out of the
whirlwind and asks the patriarch to answer Him--

Canst thou bind the sweet influences of the Pleiades, or loose the
bands of Orion?
Canst thou bring forth Mazzaroth in his season? or canst thou guide
Arcturus with his sons?
Knowest thou the ordinances of heaven? canst thou set the dominion
thereof in the earth?

Admiral Smyth says that this noble passage is more correctly rendered as
follows:

Canst thou bind the delightful teemings of Cheemah?
Or the contractions of Chesil canst thou open?
Canst thou draw forth Mazzaroth in his season
Or Ayeesh and his sons canst thou guide?

He writes: 'In this very early description of the cardinal
constellations, _Cheemah_ denotes Taurus with the Pleiades; _Chesil_ is
Scorpio; Mazzaroth is Sirius in "the chambers of the south;" and Ayeesh
the Greater Bear, the Hebrew word signifying a _bier_, which was shaped
by the four well-known bright stars, while the three forming the tail
were considered as children attending a funeral.' The Greeks at an early
period were attracted by this cluster of stars, and Hesiod alludes to
them in his writings. One passage converted into rhyme reads as follows:

There is a time when forty days they lie,
And forty nights, conceal'd from human eye;
But in the course of the revolving year,
When the swain sharps the scythe, again appear.

Their heliacal rising was considered a favourable time for setting out
on a voyage, and their midnight culmination, which occurred shortly
after the middle of November, was celebrated by some nations with
festivals and public ceremonies. Considerable diversity of opinion
existed among the ancients with regard to the number of stars which
constitute this group. It was affirmed by some that only six were
visible, whilst others maintained that seven could be seen. Ovid writes:

Quae septem dici, sex tamen esse solent.

Homer and Attalus mention six; Hipparchus and Aratus seven. The legend
with regard to the lost Pleiad would seem to indicate that, during a
period in the past, the star possessed a superior brilliancy and was
more distinctly visible than it is at the present time. This may have
been so, for, should it belong to the class of variable stars, there
would be a periodic ebb and flow of its light, by which its fluctuating
brilliance could be explained. When looked at directly only six stars
can be seen in the group, but should the eye be turned sideways more
than this number become visible. Several observers have counted as many
as ten or twelve, and it is stated by Kepler that his tutor, Maestlin,
was able to enumerate fourteen stars and mapped eleven in their relative
positions. With telescopic aid the number is largely increased--Galileo
observed thirty-six with his instrument and Hooke, in 1664, counted
seventy-eight. Large modern telescopes bring into view several thousand
stars in this region.

The Pleiades are situated at a profound distance in space. Their light
period is estimated at 250 years, indicating a distance of 1,500
billions of miles. Our Sun if thus far removed would be reduced to a
tenth-magnitude star. 'There can be little doubt,' says Miss Agnes
Clerke, 'that the solar brilliancy is surpassed by sixty to seventy of
the Pleiades. And it must be in some cases enormously surpassed; by
Alcyone 1,000, by Electra 480, by Maia nearly 400 times. Sirius itself
takes a subordinate rank when compared with the five most brilliant
members of a group, the real magnificence of which we can thus in some
degree apprehend.' This is the only star cluster which can be perceived
to be moving in space, or which has an ascertained common proper motion.
Its constituents form a magnificent system in which the stars bear a
mutual relationship to each other, and perform intricate internal
revolutions, whilst they in systemic union drift along through the
depths of space. There are two allusions to the Pleiades in 'Paradise
Lost.' In describing the path of the newly created Sun, Milton
introduces them as indicative of the joyfulness associated with the
birth of the Universe--

First in his east the glorious lamp was seen,
Regent of day, and all the horizon round
Invested with bright rays, jocund to run
His longitude through heaven's high road; the grey
Dawn, and the Pleiades before him danced,
Shedding sweet influence.--vii. 370-75.

It was believed that the Earth was created in the spring; and towards
the end of April this group rises a little before the Sun and precedes
him in his course, 'shedding sweet influences.' The ancients believed
that the good or evil influences of the stars were exercised not in the
night but during the day, when their rays mingled with those of the Sun.
The pernicious influence of the Dog-star is mentioned by Latin writers
as being most pronounced during the dog-days, at the end of summer and
commencement of autumn, the time of the heliacal rising of this star.

The other allusion to the Pleiades is in Book X., line 673, where
Milton, in describing the altered path of the Sun consequent upon the
Fall, mentions how the orb travels through Taurus with the Seven
Atlantic Sisters--the seven daughters of Atlas, the Pleiades, which are
situated on the shoulder of the animal representing this zodiacal
constellation.


THE GALAXY

The Galaxy or Milky Way is the great luminous zone encircling the
heavens, which can be seen extending across the sky from horizon to
horizon. Its diffused nebulous appearance caused the ancients much
perplexity, and many quaint opinions were hazarded as to the nature of
this celestial highway; but the mystery associated with it was not
solved until Galileo directed his newly invented telescope to this
lucent object, when, to his intense delight, he discovered that it
consists of myriads of stars--millions upon millions of suns so distant
as to be individually indistinguishable to ordinary vision, and so
closely aggregated, that their blended light gives rise to the milky
luminosity signified by its name. This stelliferous zone almost
completely encircles the sphere, which it divides into two nearly equal
parts, and is inclined at an angle of 63 deg. to the celestial equator. In
Centaurus it divides into two portions, one indistinct and of
interrupted continuity, the other bright and well defined; these, after
remaining apart for 120 deg., reunite in Cygnus. The Milky Way is of
irregular outline and varies in breadth from 5 deg. to 16 deg.; it intersects
the equinoctial in the constellations Monoceros and Aquila, and
approaches in Cassiopeia to within 27 deg. of the north pole of the heavens;
an equal distance intervenes between it and the south pole. Its poles
are in Coma Bernices and Cetus. The stars in the galactic tract are very
unevenly distributed; in some of its richest regions as many stars as
are visible to the naked eye on a clear night have been counted within
the space of a square degree. In other parts they are much less
numerous, and there have been observed besides, adjacent to the most
luminous portions of the zone, dark intervals and winding channels
almost entirely devoid of stars. An instance of this kind occurs in the
constellation of the Southern Cross, where there exists in a rich
stellar region a large oval-shaped dark vacuity, 8 deg. by 5 deg. in extent,
that appears to be almost entirely denuded of stars. In looking at it,
an impression is created that one is gazing into an empty void of space
far beyond the Milky Way. This gulf of Cimmerian darkness was called by
early navigators the Coal Sack. Similar dark spaces, though not of such
magnitude, are seen in Ophiuchus, Scorpio, and Cygnus.

The Galaxy, when viewed with a powerful telescope, is found to consist
of congeries of stars, vast stellar aggregations, great luminous tracts
resolvable into clouds of stars of overpowering magnificence, superb
clusters of various orders, and convoluted nebulous streams wandering
'with mazy error' among 'islands of light and lakes of darkness,'
resolved by the telescope into banks of shining worlds. The concourses
of stars which enter into the formation of this wonderful zone exhibit
in a marvellous degree the amazing profusion in which these orbs exist
in certain regions of space; yet those multitudes of stars perform their
motions in harmonious unison and in orderly array, and by their mutual
attraction sustain the dynamical equilibrium of this stupendous galactic
ring, the diameter of which, according to one authority, is not
traversed by light in less than 13,000 years.

[Illustration: FIG. 8.--A Portion of the Milky Way.]

Sir William Herschel, to whom we are indebted for most of what we know
of the Milky Way, commenced a series of observations in 1785 with the
object of acquiring a knowledge of the structure of the sidereal
heavens. In the accomplishment of this object, to which he devoted a
considerable part of his life, he undertook a systematic survey of that
portion of the Galaxy which is visible in the Northern Hemisphere. By a
method called star-gauging, which consisted in the enumeration of the
stars in each successive telescopic field as the instrument moved slowly
over the region under observation, he found that the depth of the star
strata could be approximately ascertained by counting the stars along
the line of vision; those were most numerous where the visual line
appeared of the greatest length and fewest in number where it was
shortest. Herschel perceived the internal structure of the Galaxy to be
exceedingly intricate and complex, and that it embraced within its
confines an endless variety of systems, clusters, and groups, branches,
sprays, arches, loops, and streaming filaments of stars, all of which
combined to form this luminous zone. 'It is indeed,' says a well-known
astronomer, 'only to the most careless glance, or when viewed through an
atmosphere of imperfect transparency, that the Milky Way seems a
continuous zone. Let the naked eye rest thoughtfully on any part of it,
and, if circumstances be favourable, it will stand out rather as an
accumulation of patches and streams of light of every conceivable
variety of form and brightness, now side by side, now heaped on each
other; again spanning across dark spaces, intertwining and forming a
most curious and complex network; and at other times darting off into
the neighbouring skies in branches of capricious length and shape which
gradually thin away and disappear.' Sir John Herschel, who was occupied
for four years at the Cape of Good Hope in exploring the celestial
regions of the Southern Hemisphere, describes the coming on of the Milky
Way as seen in his 20-foot reflector. He first remarks 'that all the
stars visible to us, whether by unassisted vision or through the best
telescopes, belong to and form part of a vast stratum or considerably
flattened and unsymmetrical congeries of stars in which our system is
deeply and eccentrically plunged; and, moreover, situated near a point
where the stratum bifurcates or spreads itself out into two sheets.' 'As
the main body of the Milky Way comes on the frequency and variety of
those masses (nebulous) increases; here the Milky Way is composed of
separate or slight or strongly connected clouds of semi-nebulous light,
and, as the telescope moves, the appearance is that of clouds passing in
a scud, as sailors call it.' The Milky Way is like sand, not strewed
evenly as with a sieve, but as if flung down by handfuls (and both hands
at once), leaving dark intervals, and all consisting of stars of the
fourteenth, sixteenth, twentieth magnitudes down to nebulosity, in a
most astonishing manner. After an interval of comparative poverty, the
same phenomenon, and even more remarkable, I cannot say it is nebulous,
it is all resolved, but the stars are inconceivably numerous and minute;
there must be millions and all almost equally massed together. Yet they
nowhere run to nuclei or clusters much brighter in the middle. Towards
the end of the seventeenth hour (Right Ascension) the globular clusters
begin to come in; they consist of stars of excessive minuteness, but
yet not more so than the ground of the Milky Way, on which not only they
appear projected, but of which it is very probable they form a part.
'From the foregoing analysis of the telescopic aspect of the Milky Way
in this interesting region, I think it can hardly be doubted that it
consists of portions differing exceedingly in distance, but brought by
the effect of projection into the same, or nearly the same, visual line;
in particular, that at the anterior edge of what we have called the main
stream, we see foreshortened a vast and illimitable area scattered over
with discontinuous masses and aggregates of stars in the manner of the
cumuli of a mackerel sky, rather than of a stratum of regular thickness
and homogeneous formation.'

The profound distance at which the stars of the Galaxy are situated in
space precludes the possibility of our obtaining any definite knowledge
of their magnitude and of the extent of the intervals by which they are
separated from each other, nor can we learn anything of the details
associated with the systems and combinations into which they enter. It
is believed that the majority of the stars in the Milky Way equal or
surpass the Sun in brilliancy and splendour. They are tenth to fifteenth
magnitude stars; now, the Sun at the distance indicated by these
magnitudes would in the telescope appear a much fainter object; he would
not reach the fifteenth magnitude. Consequently, the galactic stars are
regarded as his peers or superiors in magnitude and brilliancy. Those
myriads of suns are all in motion--in nature a stationary body is
unknown--and they are sufficiently far apart so as not to be unduly
influenced by their mutual gravitational attraction; a distance perhaps
equal to that which separates our Sun from the nearest fixed star may
intervene between each of those orbs. In the deepest recesses of the
Milky Way, Sir William Herschel was able to count 500 stars receding in
regular order behind each other; between each there existed an interval
of space, probably not less extensive than the interstellar spaces among
the stars by which we are surrounded.

The richest galactic regions in the Northern Hemisphere are found in
Perseus, Cygnus, and Aquila. Night after night could be spent in
sweeping the telescope over fields where the stars can be seen in
amazing profusion. In the interval of a quarter of an hour, Sir William
Herschel observed 116,000 stars pass before him in the telescope, and on
another occasion he perceived 258,000 stars in the space of forty-one
minutes. In the constellation of the Swan there is a region about 5 deg. in
breadth which contains 331,000 stars. Photography reveals in a
remarkable manner the amazing richness of this stelliferous zone; the
impress of the stars on the sensitive plate of the camera, in some
instances, resembles a shower of descending snowflakes.

Though Sir William Herschel was able to fathom the Galaxy in most of its
tracts, yet there were regions which his great telescopes were unable
to penetrate entirely through. In Cepheus there is a spot where he
observed the stars become 'gradually less till they escape the eye so
that appearances here favour the idea of a succeeding more distant
clustering part.' He perceived another in Scorpio 'where, through the
hollows and deep recesses of its complicated structure, we behold what
has all the appearance of a wide and indefinitely prolonged area strewed
over with discontinuous masses and clouds of stars which the telescope
at length refuses to analyse.' The Great Cluster in Perseus, which lies
in the Milky Way, also baffled the penetrative capacity of Herschel's
instruments. We cannot help quoting Professor Nichol's description of
Herschel's observation of this remarkable object. He says: 'In the Milky
Way, thronged all over with splendours, there is one portion not
unnoticed by the general observer, the spot in the sword-hand of
Perseus. That spot shows no stars to the naked eye; the milky light
which glorifies it comes from regions to which unaided we cannot pierce.
But to a telescope of considerable power the space appears lighted up
with unnumbered orbs; and these pass on through the depths of the
infinite, until, even to that penetrating glass, they escape all
scrutiny, withdrawing into regions unvisited by its power. Shall we
adventure into these deeper retirements? Then, assume an instrument of
higher efficacy, and lo! the change is only repeated; those scarce
observed before appear as large orbs, and, behind, a new series begins,
shading gradually away, leading towards farther mysteries! The
illustrious Herschel penetrated on one occasion into this spot, until he
found himself among depths whose light could not have reached him in
much less than 4,000 years; no marvel that he withdrew from the pursuit,
conceiving that such abysses must be endless!' The Milky Way may be
regarded as a universe by itself, and our Sun as one of its myriad
stars.

Milton was aware of the stellar constitution of the Milky Way, which was
one of Galileo's discoveries. The poet gives a singularly accurate
description of this luminous path, which he glorifies as the way by
which the Deity returned up to the Heaven of Heavens after He finished
His great work of creation--

So sung
The glorious train ascending: He through Heaven,
That opened wide her blazing portals, led
To God's eternal house direct the way--
A broad and ample road, whose dust is gold,
And pavement stars, as stars to thee appear
Seen in the Galaxy, that Milky Way
Which nightly as a circling zone thou seest
Powdered with stars.--vii. 573-81.


COMETS

Records of the appearance of these remarkable objects have been handed
down from earliest times; and when one of those mysterious visitors,
travelling from out the depths of space, became visible in our skies, it
was regarded with apprehension and dread as betokening the occurrence
of calamities and direful events among the nations of the Earth.

The word comet is derived from the Greek {kome}, signifying
'hair,' to which the hazy, luminous appearance of those objects bears
some resemblance. A comet consists of a bright central part called the
_nucleus_; this is surrounded by layers of nebulous matter called the
_coma_, and both combined form the _head_, from which a long appendage
extends called the _tail_. The nucleus and tail are not essential parts
of a comet, for many have been observed in which both have been wanting.
The tail is frequently very conspicuous, and presents considerable
diversity both as regards its appearance and length. In some comets it
is entirely absent, and in others it has been observed to stretch over
an arc of sixty or seventy degrees, indicating a length of 100 to 150
million miles. Sometimes it is straight, and at other times it is curved
at the extremity; it has been observed bifurcated into two branches;
and, on rare occasions, comets have been seen with two or more tails.
The tail of a comet is always directed away from the Sun; it increases
in size as the comet approaches the orb, and diminishes as it recedes
from him. This depends upon the degree of heat to which the comet is
exposed, which has the effect of driving off or evaporating some of the
matter composing the head. During the time the comet is travelling round
the Sun there is a continuous emission of this highly attenuated matter,
which is visible as the tail, but when the comet begins to recede from
the orb and reaches cooler regions of space the tail diminishes in size
as the temperature becomes reduced, and ultimately it disappears.

The appearance of a comet in the sky is often sudden and unexpected, and
one of those erratic wanderers may become visible at any time and in any
part of the heavens. It was remarked by Kepler that there are as many
comets in the sky as there are fishes in the ocean. This may or may not
be true, for they only become visible when they approach the Sun, and
the time during which they remain so does not usually exceed a few weeks
or months. Ancient astronomers were much perplexed with the motions of
comets, which appeared to be much more irregular than those of other
celestial bodies and unconformed to any known laws. Tycho Brahe believed
that comets moved in circular orbits, and Kepler imagined that they
travelled in straight lines outwards from the Sun. Newton, however, was
able to demonstrate that any conic section can be described about the
Sun consistent with the law of gravitation, and that the orbits of
comets correspond with three of the four sections into which a cone can
be divided. Consequently, they obey the laws of planetary motion. Comets
which move in ellipses of known eccentricity and return with periodical
regularity may be regarded as belonging to the solar system. Twenty of
these are known, and eleven of them have more than once passed their
perihelion. Those most familiarly known complete their periods in years
as follows:--Encke's 3.3; Swift's, 5.5; Winnecke's, 5.6; Tempel's, 6;
Brorsen's, 5.5; Faye's, 7.4; Tuttle's, 13.8, and Halley's, 76. Comets
with parabolic and hyperbolic orbits may be regarded as stray objects
which visit our system once, and depart never to return again. Besides
those already mentioned there are many comets with orbits of such marked
eccentricity that their ellipses when near perihelion cannot be
distinguished from parabolae. The great comets of 1780, 1811, 1843, 1858,
1861, and 1882 traverse orbits approaching this form, and some of them
require hundreds and thousands of years to accomplish a circuit of their
paths.

Numerous instances of the appearance of remarkable comets have been
recorded in the annals of ancient nations. The earliest records of
comets are by the Chinese, who were careful observers of celestial
phenomena. A comet is said to have appeared at the time of the birth of
Mithridates (134 B.C.), which had a disc as large as that of the Sun; a
great comet also became visible in the heavens about the time of the
death of Julius Caesar (44 B.C.), and another was seen in the reign of
Justinian (531 A.D.). A remarkable comet was observed in 1106, and in
1456, the year in which the Turks obtained possession of Constantinople
and threatened to overrun Europe, a great comet appeared, which was
regarded by Christendom with ominous forebodings. The celebrated
astronomer Halley was the first to predict the return of a comet.
Having become acquainted with Newton's investigations, which showed that
the forms of the orbits of comets were either parabolae or extremely
elongated ellipses, he subjected the next great comet, which appeared in
1682, to a series of observations, calculated its orbit, and predicted
that it would return to perihelion in seventy-five or seventy-six years.
On referring to past records he discovered that a great comet appeared
in 1607, which pursued a path similar to the one traced out for his
comet, another was seen in 1531, and one in 1456. Halley perceived that
the intervals between those dates corresponded to a period of about
seventy-six years, the time which he calculated would be required for
his comet to complete a revolution of its orbit. He therefore had no
hesitation in predicting that the comet would appear again in 1758.
Halley knew that he would not be alive to witness the event, and alludes
to it in the following sentence: 'Wherefore if it should return
according to our prediction about the year 1758, impartial posterity
will not refuse to acknowledge that this was first discovered by an
Englishman.' As the time approached when the comet should be drawing
near to our system, much interest was excited among astronomers, who
would have an opportunity afforded them of testing the accuracy of
Halley's prediction. An eminent French mathematician named Clairaut
computed anew, by a method rather different to that adopted by Halley,
the retarding effect of the attraction of the planets upon the speed of
the comet, and arrived at the conclusion that it would reach perihelion
about the middle of April 1759; but, owing to unknown influences--Uranus
and Neptune not having been discovered--it might be a month before or
behind the calculated time. Clairaut made this announcement on November
14, 1758. Astronomers were now intently on the look-out for the comet,
and night after night the sky was swept by telescopes in search of the
expected visitor, which for upwards of seventy years had been pursuing
its solitary path invisible to mortal eyes. But the mental vision of the
mathematician did not fail to follow this celestial object, which was
now announced as being on the confines of our system. The comet was
first observed on December 25, 1758, it soon became conspicuous in the
heavens, and reached perihelion on March 12, 1759, a month before the
time assigned to it by Clairaut but within the limit of error allowed
for unknown influences. Halley's comet returned again in 1835, and may
be expected about the year 1911. The periodic appearance of this comet
has been traced back to the year 1305.

The celebrated comet of 1680 was noted as having been the one which
afforded Newton an opportunity of making observations which led to his
discovery that comets describe orbits round the Sun in conformity with
the different sections of a cone. The comet of 1811 was observed for
many weeks in the northern heavens as a brilliant object with a
beautiful fan-shaped tail; it completes a revolution of its orbit in
about 3,000 years. The comet of 1843 was also a splendid object. It
possessed a tail 200 million miles in length, and approached within
32,000 miles of the Sun. The heat to which it was exposed was sufficient
to volatilize the most infusible substances known to exist. Donati's
comet of 1858 will be long remembered as one of the most impressive of
celestial spectacles: its tail extended over an area of forty degrees,
and enveloped the star Arcturus, which could be seen shining through it
with undiminished brilliancy. Its period is estimated to be 2,100 years.
A great comet appeared in 1861, through the tail of which the Earth
passed without any perceptible effect having resulted. No remarkable
comets have appeared during recent years. In 1880, 1881, and 1882,
several were observed, and that of 1881 was the first successfully
photographed.

Comets consist of cosmical matter which exists in a condition of extreme
tenuity, and especially so in the coma and tail. Sir John Herschel
described them as almost spiritual in texture, and small stars have been
seen shining through their densest parts without any perceptible
diminution of their light. The nucleus is believed to be composed of a
congeries of meteoric fragments, and these, when exposed to the Sun's
heat, throw off luminous nebulous particles that are swept by some
repulsive force into space and form the appendage known as the tail.
Comets may be regarded as celestial objects that are perfectly
innocuous. Neither fear nor dread need be apprehended from their visits;
they come to please and instruct, not to injure or destroy.

Milton does not fail to introduce into his poem several allusions to
comets, and in doing so expresses the ideas and sentiments which in his
time were associated with those objects.

In describing the hostile meeting between Satan and Death before the
Gates of Hell, he writes:

On the other side,
Incensed with indignation, Satan stood
Unterrified, and like a comet burned,
That fires the length of Ophiuchus huge
In the arctic sky, and from his horrid hair
Shakes pestilence and war.--ii. 706-11.

This passage is eminently descriptive of the appearance of a great
comet, and the occasion on which it is introduced adds to the intensity
of the lurid imaginings and feelings of terror and dismay with which
these objects have always been regarded. The comparison of the enraged
Prince of Hell with one of those mysterious and fiery looking visitors
to our skies was a grand conception of the poet's, and one worthy of the
mighty combatant. Ophiuchus (the Serpent-bearer) is a large
constellation which occupies a rather barren region of the heavens to
the south of Hercules. It has a length of about forty degrees, and is
represented by the figure of a man bearing a serpent in both hands. It
is not easy to imagine why Milton should have assigned the comet to
this uninteresting constellation; he may possibly have seen one in this
part of the sky, or his poetical ear may have perceived that the
expression 'Ophiuchus huge,' which has about it a ponderous rhythm, was
well adapted for the poetic description of a comet.

The only other allusion in the poem to a comet is near its conclusion,
when the Cherubim descend to take possession of the Garden, prior to the
removal of Adam and Eve--

High in front advanced,
The brandished sword of God before them blazed,
Fierce as a comet; which with torrid heat,
And vapour as the Lybian air adust
Began to parch that temperate clime.--xii. 632-36.


FALLING STARS

On any clear night an observer can, by attentively watching the heavens,
perceive a few of those objects which become visible for a moment as a
streak of light and then vanish. They are the result of the combustion
of small meteoric masses having a celestial origin, and travelling with
cosmical velocity, and which, in their headlong flight, become so heated
by contact with the Earth's atmosphere that they are converted into
glowing vapour. This vapour when it cools condenses into fine powder or
dust, and gradually descends upon the Earth's surface, where it can be
detected.

Shooting stars become visible at a height varying between twenty and one
hundred and thirty miles, and their average velocity has been estimated
at about thirty miles a second. Though casual falling stars can be seen
at all times in every part of the heavens, yet there are certain periods
at which they appear in large numbers, and have been observed to radiate
from certain well-defined parts of the sky. When the radiant point is
overhead, the falling stars spread out and resemble a parachute of fire;
but when it is below the horizon, the stars ascend upwards like rockets
into the sky. The radiant point is fixed among the stars, so that at the
commencement of a shower it may be overhead, and before the termination
of the display it may have travelled below the horizon. The radiant is
usually named after the constellation in which it is observed.

The November meteors are called Leonids, because they radiate from a
point in the constellation Leo; those in Taurus are called Taurids; in
Perseus, Perseids; in Lyra, Lyraids; and in Andromeda, Andromedes,
because their radiant points are situated in those constellations.

The falling stars that have attracted most attention are those which
appear on or about November 13. Every year at this period they can be
seen in greater or less numbers, and on referring to numerous past
records it has been ascertained that a magnificent display of those
objects occurs every thirty-three years. The earliest historical
allusion to this meteoric shower is by Theophanes, who wrote that in the
year 472 A.D. the sky at Constantinople appeared to be on fire with
falling stars. In the year 902 A.D. another remarkable display took
place, and from that time until 1833 twelve conspicuous displays are
recorded as having occurred at recurring intervals of thirty-three
years. The grandest display of this kind that was ever witnessed
occurred in 1833. It was visible over nearly the whole of the American
continent, and, having commenced at midnight, lasted for four or five
hours. The falling stars were so numerous that they appeared to rain
upon the Earth, and caused the utmost consternation and terror among
those who witnessed the phenomenon, many persons having imagined that
the end of the world was at hand. The regular recurrence of these
meteoric displays has been satisfactorily explained by the assumption
that round the Sun there travels in an elliptical orbit with planetary
velocity a vast shoal of meteoric bodies some millions of miles in
length and several hundred thousand miles in breadth. The nearest point
of their orbit to the Sun coincides with the Earth's orbit, and the most
distant part extends beyond the orbit of Uranus. These bodies accomplish
a circuit of their orbit in 33-1/4 years. The Earth in her annual
revolution intersects the path of the meteors, and when this occurs some
falling stars can always be seen; but when the intersection happens at
the time the shoal is passing, then there results a grand meteoric
display. Numerous other meteoric swarms travel in orbital paths round
the Sun.

Milton, in his poem, alludes to falling stars upon two occasions. In
describing the fall of Mulciber from Heaven he says:--

from morn
To noon he fell, from noon to dewy eve,
A summer's day; and with the setting sun
Dropt from the zenith like a falling star,
On Lemnos the AEgaean isle.--i. 742-46.

The rapid flight of the archangel Uriel from the Sun to the Earth is
described in the following lines:--

Thither came Uriel, gliding through the even
On a sunbeam, swift as a shooting star
In autumn thwarts the night, when vapours fired
Impress the air, and shows the mariner
From what point of his compass to beware
Impetuous winds.--iv. 555-60.

Milton mentions the season of the year in which those stars are most
frequently seen, and refers to an ancient belief by which they were
regarded as the precursors of stormy weather. A translation from Virgil
contains a similar allusion to them--

Oft shalt thou see ere brooding storms arise,
Star after star glide headlong down the skies.

The standard borne by the Cherub Azazel is described as having--

Shone like a meteor streaming to the wind.--i. 537.