[Sidenote: The distribution of the Stars into 6 classes.]
[Sidenote: Of _Telescopical Stars_.]
The astronomers distribute the Stars into several orders or classes;
those that are nearest to us, and appear brightest to the eye, are
called Stars of the first magnitude; those that are nearest to them
in brightness and lustre, are called Stars of the second magnitude;
those of the third class, are stiled Stars of the third magnitude;
and so on, until we come to the Stars of the sixth magnitude, which
are the smallest that can be discerned by the naked eye. There are
infinite numbers of smaller Stars, that can be seen through telescopes;
but these are not reduced to any of the six orders, and are only
called _Telescopical Stars_. It may be here observed, that tho’ the
astronomers have reduced all the Stars that are visible to the naked
eye, into some one or other of these classes, yet we are not to
conclude from thence that all the Stars answer exactly to some or other
of these orders; but there may be in reality as many orders of the
Stars, as they are in number, few of them appearing exactly of the same
bigness and lustre.
[Sidenote: The Stars digested into constellations]
The ancient astronomers, that they might distinguish the Stars, in
regard to their situation and position to each other, divided the
whole starry firmament into Several _Asterisms_, or systems of Stars,
consisting of those that are near to one another. These _Asterisms_
are called _Constellations_, and are digested into the forms of some
animals; as Men, Lyons, Bears, Serpents, _&c._ or to the images of some
known things; as, of a Crown, a Harp, a Triangle, _&c._
[Sidenote: _Zodiac._]
The starry firmament was divided by the ancients into 48 images,
or constellations; twelve of which they placed in that part of the
Heavens wherein are the planes of the Planetary orbits; which part is
called the _Zodiac_, because most of the constellations placed therein
resemble some living creature. The two regions of the Heavens that are
on each side of the _Zodiac_, are called the North and South parts of
the Heavens.
[Sidenote: Constellations within the Zodiac.]
The constellations within the _Zodiac_ are, 1. _Aries_, the _Ram_;
2. _Taurus_, the _Bull_; 3. _Gemini_, the _Twins_; 4. _Cancer_, the
_Crab_; 5. _Leo_, the _Lion_; 6. _Virgo_, the _Virgin_; 7. _Libra_,
the _Balance_; 8. _Scorpio_, the _Scorpion_; 9. _Sagittarius_,
the _Archer_; 10. _Capricornus_, the _Goat_; 11. _Aquarius_, the
_Water-Bearer_; and, 12. _Pisces_, the _Fishes_.
[Sidenote: Northern constellations.]
The constellations on the North side of the _Zodiac_ are Twenty-one,
_viz._ the _Little Bear_; the _Great Bear_; the _Dragon_; _Cepheus_, a
king of _Ethiopia_; _Bootes_, the keeper of the _Bear_; the _Northern
Crown_; _Hercules_ with his Club, watching the _Dragon_; the _Harp_;
the _Swan_; _Cassiopeia_; _Persius_; _Andromeda_; the _Triangle_;
_Auriga_; _Pegasus_, or the _Flying Horse_; _Equuleus_; the _Dolphin_;
the _Arrow_; the _Eagle_; _Serpentarius_; and the _Serpent_.
[Sidenote: Southern constellations.]
The constellations noted by the ancients on the South side of the
_Zodiac_, were fifteen, _viz._ the _Whale_; the river _Eridanus_;
the _Hare_; _Orion_; the _Great Dog_; _Little Dog_; the Ship _Argo_;
_Hydra_; the _Centaur_; the _Cup_; the _Crow_; the _Wolf_; the
_Altar_; the _Southern Crown_; and the _Southern Fish_. To these have
been lately added the following, _viz._ The _Phœnix_; the _Crane_;
the _Peacock_; the _Indian_; the _Bird of Paradise_; the _Southern
Triangle_; the _Fly_; _Cameleon_; the _Flying Fish_; _Toucan_, or
the _American Goose_; the _Water Serpent_, and the _Sword Fish_. The
ancients placed those particular constellations or figures in the
Heavens, either to commemorate the deeds of some great man, or some
notable exploit or action; or else took them from the fables of their
religion, _&c_. And the modern astronomers do still retain them, to
avoid the confusion that would arise by making new ones, when they
compare the modern observations with the old ones.
[Sidenote: _Unformed Stars._]
Some of the principal Stars have particular names given them, as
_Syrius_, _Arcturus_, _&c._ There are also several Stars that are not
reduced into constellations, and these are called _Unformed Stars_.
[Sidenote: The _Galaxy_, or _Milky Way_.]
Besides the Stars visible to the naked eye, there is a very remarkable
space in the Heavens, called the _Galaxy_, or _Milky Way_. This is a
broad circle of a whitish hue, like milk, going quite round the whole
Heavens, and consisting of an infinite number of small Stars, visible
thro’ a telescope, tho’ not discernable by the naked eye, by reason
of their exceeding faintness; yet with their light they combine to
illustrate that part of the Heavens where they are, and to cause that
shining whiteness.
The places of the fixed Stars, or their relative situations one from
another, have been carefully observed by astronomers, and digested into
catalogues. The first among the _Greeks_, who reduced the Stars into
a catalogue, was _Hypparchus_, who, from his own observations, and of
those who lived before him, inserted 1022 Stars into his catalogue,
about 120 years before the Christian _Æra_: This catalogue has been
since enlarged and improved by several learned men, to the number of
3000, of which there are a great many telescopical, and not to be
discerned by the naked eye; and these are all ranked in the catalogue
as the Stars of the seventh magnitude.
It may seem strange to some, that there are no more than this number
of Stars visible to the naked eye; for sometimes in a clear night
they seem to be innumerable: but this is only a deception of our
sight, arising from their vehement sparkling, while we look upon them
confusedly, without reducing them into any order; for there can seldom
be seen above 1000 Stars in the whole Heavens with the naked eye at the
same time; and if we should distinctly view them, we shall not find
many but what are inserted upon a good _Celestial_ Globe.
Altho’ the number of Stars that can be discerned by the naked eye
are so few, yet it is probable there are many more which are beyond
the reach of our optics, for through telescopes they appear in vast
multitudes, every where dispersed throughout the whole Heaven; and
the better our glasses are, the more of them we still discover. The
ingenious Dr. _Hook_ has observed 78 Stars in the _Pleiades_, of
which the naked eye is never able to discern above 7; and in _Orion_,
which has but 80 Stars in the _British_ catalogue (and some of them
telescopical) there has been numbered 2000 Stars.
[Sidenote: An idea of the Universe.]
Those who think that all these glorious bodies were created for no
other purpose than to give us a little dim light, must entertain a
very slender idea of the Divine Wisdom; for we receive more light from
the _Moon_ itself, than from all the _Stars_ put together. And since
the _Planets_ are subject to the same laws of motion with our _Earth_,
and some of them not only equal, but vastly exceed it in magnitude,
it is not unreasonable to suppose, that they are all habitable Worlds.
And since the _Fixed Stars_ are no ways behind our _Sun_, either in
bigness or lustre, is it not probable, that each of them have a system
of _Planetary Worlds_ turning round them, as we do round our Sun? And
if we ascend as far as the smallest Star we can see, shall we not then
discover innumerable more of these glorious bodies, which now are
altogether invisible to us? And so _ad infinitum_, thro’ the boundless
space of the universe. What a magnificient idea must this raise in us
of the _Divine Being_! Who is every where, and at all times present,
displaying his Divine Power, Wisdom and Goodness, amongst all his
Creatures!
[Illustration]
_The_ DESCRIPTION _and_ USE _of the_ CELESTIAL _and_ TERRESTRIAL GLOBES.
[Sidenote: _Globe_ or _Sphere_.]
A _Globe_ or _Sphere_ is a round solid body, having every part of its
surface equally distant from a point within it, called its _Center_;
and it may be conceived to be formed by the revolution of a semicircle
round its diameter.
[Sidenote: _Great Circle._]
[Sidenote: _Hemispheres._]
Any circle passing through the center of the sphere, thereby dividing
into two equal parts or segments, is called a _Great Circle_; and the
segments of the sphere so divided, are called _Hemispheres_.
Every great circle has its Poles and Axis.
[Sidenote: _Poles._]
The _Poles_ of a great circle are two points on the surface of the
sphere, diametrically opposite to one another, and every where equally
distant from the said circle.
[Sidenote: _Axis._]
The _Axis_ of a circle is a right line passing through the center of
the sphere, and through the Poles of the said circle, and is therefore
perpendicular to the Plane: Therefore
[Sidenote: _Secundaries._]
All circles passing through the Poles of any great circle, intersect
it in two places diametrically opposite, and also at right angles;
and with respect to the said great circle, they may be called its
_Secundaries_.
[Sidenote: _Parallel_ or _lesser Circles_.]
All circles dividing the sphere into two unequal parts, are called
_lesser_ or _parallel Circles_, and are usually denominated by that
great circle to which they are parallel.
[Sidenote: _Terrestrial Globe._]
The Earth being globular, its outward parts, as the several
_Countries_, _Seas_, _&c._ are best, and most naturally represented
upon the surfaces of a Globe; and when such a body has the outward
parts of the Earth and Sea delineated upon its surface, and placed in
their natural order and situation, it is called a _Terrestrial Globe_.
[Sidenote: _Celestial Globe._]
The Celestial Bodies appear to us as if they were all placed in the
same concave sphere, therefore astronomers place the Stars according to
their respective situations and magnitudes, and also the images of the
constellations, upon the external surface of a Globe; for it answers
the same purposes as if they were placed within a concave sphere, if we
suppose the Globe to be transparent, and the eye placed in the center.
A Globe having the Stars placed upon its surface, as above described,
is called a _Celestial Globe_. These Globes are both placed in frames,
with other appurtenances, as shall be described in a proper place.
[Sidenote: The principal use of the Globes.]
The principal uses of the Globes (besides their serving as _Maps_, to
distinguish the outward parts of the Earth, and the situations of the
fixed Stars) is to explain and resolve the phænomena arising from the
diurnal motion of the Earth round its Axis.
[Sidenote: There will be the same prospect of the fixed Stars whether
the spectator be placed on the Earth, or in the Sun.]
It has been shewed in the Introduction, that the distance of the Earth
from the Sun, is no more than a point, when compared with the immense
distance of the fixed Stars; therefore let the Earth be in what point
soever of her orbit, there will be the same prospect of the Heavens,
as a spectator would observe did he reside in the Sun: And if several
circles be imagined to pass thro’ the center of the Earth, and others,
parallel to them, be conceived to pass thro’ the center of the Sun,
these circles in the Heavens will seem to coincide, and to pass exactly
thro’ the same Stars. Wherefore as to the appearances of the fixed
Stars, it is indifferent whether the Earth or the Sun be made the
center of the Universe. But because it is from the Earth that we always
observe the celestial bodies, and their apparent motions seem to us to
be really made in the Heavens, it is more natural in explaining the
phænomena arising from these motions, to place the Earth in the center.
And again, because the semidiameter of the Earth, when compared to her
distance from the Sun, is of no sensible magnitude, any point, upon the
Earth’s surface, let her be in what part soever of the orbit, may be
considered as being the center of the Universe. Upon these principles,
the different phænomena arising from the diurnal motion of the Earth,
and the different situation of a spectator upon its surface, are very
naturally illustrated and explained by the Globes.
As to the alterations of seasons, _&c._ arising from the annual motion
of the Earth round the Sun, it is indifferent which we suppose to move,
the Earth or the Sun, for in both cases the effect will be the same.
Wherefore because it is the Sun that appears to us to move, we say the
Sun is in such a part of the ecliptic, without attributing any motion
to the Earth, any more than if she had actually been at rest. For the
same reason we say the Sun rises, or the Sun sets; by which we mean
that he begins to appear or disappear, without considering in the least
how these effects are produced. These things are here mentioned, to
obviate the objections that might be made by beginners, after they have
been told that the Sun stands still.
[Illustration]