402. _Cloudy Stars_ are so called from their misty appearance. They look
like dim Stars to the naked eye; but through a telescope they appear
broad illuminated parts of the sky; in some of which is one Star, in
others more. Five of these are mentioned by _Ptolemy_. 1. One at the
extremity of the right hand of _Perseus_. 2. One in the middle of the
_Crab_. 3. One unformed, near the Sting of the _Scorpion_. 4. The eye of
_Sagittarius_. 5. One in the head of _Orion_. In the first of these
appear more Stars through the telescope than in any of the rest,
although 21 have been counted in the head of _Orion_, and above 40 in
that of the _Crab_. Two are visible in the eye of _Sagittarius_ without
a telescope, and several more with it. _Flamsteed_ observed a cloudy
Star in the bow of _Sagittarius_, containing many small Stars: and the
Star _d_ above _Sagittary_’s right shoulder is encompassed with several
more. Both _Cassini_ and _Flamsteed_ discovered one between the _Great_
and _Little Dog_, which is very full of Stars visible only by the
telescope. The two whitish spots near the South Pole, called the
_Magellanic Clouds_ by Sailors, which to the bare eye resemble part of
the Milky-Way, appear through telescopes to be a mixture of small Clouds
and Stars. But the most remarkable of all the cloudy Stars is that in
the middle of _Orion’s Sword_, where seven Stars (of which three are
very close together) seem to shine through a cloud, very lucid near the
middle, but faint and ill defined about the edges. It looks like a gap
in the sky, through which one may see (as it were) part of a much
brighter region. Although most of these spaces are but a few minutes of
a degree in breadth, yet, since they are among the fixed Stars, they
must be spaces larger than what is occupied by our solar System; and in
which there seems to be a perpetual uninterrupted day among numberless
Worlds which no human art ever can discover.
[Sidenote: Changes in the Heavens.]
403. Several Stars are mentioned by antient Astronomers, which are not
now to be found; and others are now visible to the bare eye which are
not recorded in the antient catalogues. _Hipparchus_ observed a new Star
about 120 years before CHRIST; but he has not mentioned in what part of
the Heavens it was seen, although it occasioned his making a catalogue
of the Stars; which is the most antient that we have.
[Sidenote: New Stars.]
The first _New Star_ that we have any good account of, was discovered by
_Cornelius Gemma_ on the 8th of _November_ A. D. 1572, in the Chair of
Cassiopea. It surpassed _Sirius_ in brightness and magnitude; and was
seen for 16 months successively. At first it appeared bigger than
_Jupiter_ to some eyes, by which it was seen even at mid-day: afterwards
it decayed gradually both in magnitude and lustre, until _March_ 1573,
when it became invisible.
On the 13th of _August_ 1596, _David Fabricius_ observed the _Stella
Mira_, or wonderful Star, in the _Neck_ of the _Whale_; which has been
since found to appear and disappear periodically, seven times in six
years, continuing in its greatest lustre for 15 days together; and is
never quite extinguished.
In the year 1600, _William Jansenius_ discovered a changeable Star in
the _Neck_ of the _Swan_; which, in time became so small as to be
thought to disappear entirely, till the years 1657, 1658, and 1659, when
it recovered its former lustre and magnitude; but soon decayed, and is
now of the smallest size.
In the year 1604 _Kepler_ and several of his friends saw a new Star near
the heel of the right foot of _Serpentarius_, so bright and sparkling
that it exceeded any thing they had ever seen before; and took notice
that it was every moment changing into some of the colours of the
rainbow, except when it was near the horizon, at which time it was
generally white. It surpassed _Jupiter_ in magnitude, which was near it
all the month of _October_, but easily distinguished from it by a steady
light. It disappeared between _October_ 1605 and the _February_
following, and has not been seen since that time.
In the year 1670, _July_ 15, _Hevelius_ discovered a new Star, which in
_October_ was so decayed as to be scarce perceptible. In _April_
following it regained its lustre, but wholly disappeared in _August_. In
_March_ 1672 it was seen again, but very small; and has not been visible
since.
In the year 1686 a new Star was discovered by _Kirch_, which returns
periodically in 404 days.
In the year 1672, _Cassini_ saw a Star in the _Neck_ of the Bull, which
he thought was not visible in _Tycho_’s time; nor when _Bayer_ made his
Figures.
[Sidenote: Cannot be Comets.]
404. Many Stars, besides those above-mentioned, have been observed to
change their magnitudes: and as none of them could ever be perceived to
have tails, ’tis plain they could not be Comets; especially as they had
no parallax, even when largest and brightest. It would seem that the
periodical Stars have vast clusters of dark spots, and very slow
rotations on their Axis; by which means, they must disappear when the
side covered with spots is turned towards us. And as for those which
break out all of a sudden with such lustre, ’tis by no means improbable
that they are Suns whose Fuel is almost spent, and again supplied by
some of their Comets falling upon them, and occasioning an uncommon
blaze and splendor for some time: which indeed appears to be the
greatest use of the cometary part of any system[86].
[Sidenote: Some Stars change their Places.]
Some of the Stars, particularly _Arcturus_, have been observed to change
their places above a minute of a degree with respect to others. But
whether this be owing to any real motion in the Stars themselves, must
require the observations of many ages to determine. If our solar System
changeth its Place, with regard to absolute space, this must in process
of time occasion an apparent change in the distances of the Stars from
each other: and in such a case, the places of the nearest Stars to us
being more affected than of those which are very remote, their relative
positions must seem to alter, though the Stars themselves were really
immoveable. On the other hand, if our own system be at rest, and any of
the Stars in real motion, this must vary their positions; and the more
so, the nearer they are to us, or the swifter their motions are; or the
more proper the direction of their motion is, for our perception.
[Sidenote: The Ecliptic less oblique now to the Equator than formerly.]
405. The obliquity of the Ecliptic to the Equinoctial is found at
present to be above a third part of a degree less than _Ptolemy_ found
it. And most of the observers after him found it to decrease gradually
down to _Tycho_’s time. If it be objected, that we cannot depend on the
observations of the antients, because of the incorrectness of their
Instruments; we have to answer, that both _Tycho_ and _Flamsteed_ are
allowed to have been very good observers: and yet we find that
_Flamsteed_ makes this obliquely 2-1/2 minutes of a degree less than
_Tycho_ did, about 100 years before him: and as _Ptolemy_ was 1324 years
before _Tycho_, so the gradual decrease answers nearly to the difference
of time between these three Astronomers. If we consider, that the Earth
is not a perfect sphere, but an oblate spheroid, having its Axis shorter
than its Equatoreal diameter; and that the Sun and Moon are constantly
acting obliquely upon the greater quantity of matter about the Equator,
pulling it, as it were, towards a nearer and nearer co-incidence with
the Ecliptic; it will not appear improbable that these actions should
gradually diminish the Angle between those Planes. Nor is it less
probable that the mutual attractions of all the Planets should have a
tendency to bring the planes of all their Orbits to a co-incidence: but
this change is too small to become sensible in many ages.