391. The Stars are said to be fixed, because they have been generally observed to keep at the same distance from each other: their apparent diurnal revolutions being caused solely by the Earth’s turning on its Axis. They appear of a sensible magnitude to the bare eye, because the retina is affected not only by the rays of light which are emitted directly from them, but by many thousands more, which falling upon our eye-lids, and upon the aerial particles about us, are reflected into our eyes so strongly as to excite vibrations not only in those points of the retina where the real images of the Stars are formed, but also in other points at some distance round about. This makes us imagine the Stars to be much bigger than they would appear, if we saw them only by the few rays which come directly from them, so as to enter our eyes without being intermixed with others. Any one may be sensible of this, by looking at a Star of the first Magnitude through a long narrow tube; which, though it takes in as much of the sky as would hold a thousand such Stars, yet scarce renders that one visible.
The more a telescope magnifies, the less is the aperture through which the Star is seen; and consequently the fewer rays it admits into the eye. Now since the Stars appear less in a telescope which magnifies 200 times than they do to the bare eye, insomuch that they seem to be only indivisible points, it proves at once both that the Stars are at immense distances from us, and that they shine by their own proper light. If they shone by borrowed light they would be as invisible without telescopes as the Satellites of Jupiter are: for these Satellites appear bigger when viewed with a good telescope than the largest fixed Stars do.
392. The number of Stars discoverable, in either Hemisphere, by the naked eye, is not above a thousand. This at first may appear incredible, because they seem to be without number: But the deception arises from our looking confusedly upon them, without reducing them into any order. For look but stedfastly upon a pretty large portion of the sky, and count the number of Stars in it, you will be surprised to find them so few. Or, if one considers how seldom the Moon meets with any Stars in her way, although there are as many about her Path as in other parts of the Heavens (the Milky way excepted) he will soon be convinced that the Stars are much thinner sown than he was aware of. The British catalogue, which, besides the Stars visible to the bare eye, includes a great number which cannot be seen without the assistance of a telescope, contains no more than 3000, in both Hemispheres.
393. As we have incomparably more light from the Moon than from all the Stars together, it were the greatest absurdity to imagine that the Stars were made for no other purpose than to cast a faint light upon the Earth: especially since many more require the assistance of a good telescope to find them out, than are visible without that Instrument. Our Sun is surrounded by a system of Planets and Comets; all which would be invisible from the nearest fixed Star. And from what we already know of the immense distance of the Stars, the nearest may be computed at 32,000,000,000,000 of miles from us which is more than a cannon bullet would fly in 7,000,000 of years. Hence ’tis easy to prove, that the Sun seen from such a distance, would appear no bigger than a Star of the first magnitude. From all this it is highly probable that each Star is a Sun to a system of worlds moving round it though unseen by us; especially, as the doctrine of a plurality of worlds is rational, and greatly manifests the Power, Wisdom, and Goodness of the great Creator.
394. The Stars, on account of their apparently various magnitudes, have been distributed into several classes or orders. Those which appear largest are called Stars of the first magnitude; the next to them in lustre, Stars of the second magnitude, and so on to the sixth, which are the smallest that are visible to the bare eye. This distribution having been made long before the invention of telescopes, the Stars which cannot be seen without the assistance of these instruments are distinguished by the name of Telescopic Stars.
395. The antients divided the starry Sphere into particular Constellations, or Systems of Stars, according as they lay near one another, so as to occupy those spaces which the figures of different sorts of animals or things would take up, if they were there delineated. And those Stars which could not be brought into any particular Constellation were called unformed Stars.
396. This division of the Stars into different Constellations or Asterisms, serves to distinguish them from one another, so that any particular Star may be readily found in the Heavens by means of a Celestial Globe; on which the Constellations are so delineated as to put the most remarkable Stars into such parts of the figures as are most easily distinguished. The number of the antient Constellations is 48, and upon our present Globes about 70. On Senex’s Globes are inserted Bayer’s Letters; the first in the Greek Alphabet being put to the biggest Star in each Constellation, the second to the next, and so on: by which means, every Star is as easily found as if a name were given to it. Thus, if the Star γ in the Constellation of the Ram be mentioned, every Astronomer knows as well what Star is meant as if it were pointed out to him in the Heavens.
397. There is also a division of the Heavens into three parts. 1. The Zodiac, (ζωδιακὸς) from ζώδιον Zodion an Animal, because most of the Constellations in it, which are twelve in number, are the figures of Animals: as Aries the Ram, Taurus the Bull, Gemini the Twins, Cancer the Crab, Leo the Lion, Virgo the Virgin, Libra the Balance, Scorpio the Scorpion, Sagittarius the Archer, Capricornus the Goat, Aquarius the Water-bearer, and Pisces the Fishes. The Zodiac goes quite round the Heavens: it is about 16 degrees broad, so that it takes in the Orbits of all the Planets, and likewise the Orbit of the Moon. Along the middle of this Zone or Belt is the Ecliptic, or Circle which the Earth describes annually as seen from the Sun; and which the Sun appears to describe as seen from the Earth. 2. All that Region of the Heavens, which is on the north side of the Zodiac, containing 21 Constellations. And 3. that on the south side, containing 15.
398. The antients divided the Zodiac into the above 12 Constellations or Signs in the following manner. They took a vessel with a small hole in the bottom, and having filled it with water, suffered the same to distil drop by drop into another Vessel set beneath to receive it; beginning at the moment when some Star rose, and continuing until it rose the next following night. The water fallen down into the receiver they divided into twelve equal parts; and having two other small vessels in readiness, each of them fit to contain one part, they again poured all the water into the upper vessel, and strictly observing the rising of some Star in the Zodiac, they at the same time suffered the water to drop into one of the small vessels; and as soon as it was full, they shifted it and set an empty one in it’s place. By this means, when each vessel was full, they observed what Star of the Zodiac rose; and though not possible in one night, yet in many, they observed the rising of twelve Stars, by which they divided the Zodiac into twelve parts.
399. The names of the Constellations, and the number of Stars observed in each of them by different Astronomers, are as follows.
| Ptolemy. | Tycho. | Hevelius. | Flamsteed. | |||
|---|---|---|---|---|---|---|
| Ursa minor | The Little Bear | 8 | 7 | 12 | 24 | |
| Ursa major | The Great Bear | 35 | 29 | 73 | 87 | |
| Draco | The Dragon | 31 | 32 | 40 | 80 | |
| Cepheus | Cepheus | 13 | 4 | 51 | 35 | |
| Bootes, Arctophilax | 23 | 18 | 52 | 54 | ||
| Corona Borealis | The northern Crown | 8 | 8 | 8 | 21 | |
| Hercules, Engonasin | Hercules kneeling | 29 | 28 | 45 | 113 | |
| Lyra | The Harp | 10 | 11 | 17 | 21 | |
| Cygnus, Gallina | The Swan | 19 | 18 | 47 | 81 | |
| Cassiopea | The Lady in her Chair | 13 | 26 | 37 | 55 | |
| Perseus | Perseus | 29 | 29 | 46 | 59 | |
| Auriga | The Waggoner | 14 | 9 | 40 | 66 | |
| Serpentarius, Ophiuchus | Serpentarius | 29 | 15 | 40 | 74 | |
| Serpens | The Serpent | 18 | 13 | 22 | 64 | |
| Sagitta | The Arrow | 5 | 5 | 5 | 18 | |
| Aquila, Vultur | The Eagle | 15 | 12 | 23 | 71 | |
| Antinous | Antinous | 3 | 19 | |||
| Delphinus | The Dolphin | 10 | 10 | 14 | 18 | |
| Equulus, Equi sectio | The Horse’s Head | 4 | 4 | 6 | 10 | |
| Pegasus, Equus | The Flying Horse | 20 | 19 | 38 | 89 | |
| Andromeda | Andromeda | 23 | 23 | 47 | 66 | |
| Triangulum | The Triangle | 4 | 4 | 12 | 16 | |
| Aries | The Ram | 18 | 21 | 27 | 66 | |
| Taurus | The Bull | 44 | 43 | 51 | 141 | |
| Gemini | The Twins | 25 | 25 | 38 | 85 | |
| Cancer | The Crab | 23 | 15 | 29 | 83 | |
| Leo | The Lion | 35 | 30 | 49 | 95 | |
| Coma Berenices | Berenice’s Hair | 14 | 21 | 43 | ||
| Virgo | The Virgin | 32 | 33 | 50 | 110 | |
| Libra, Chelæ | The Scales | 17 | 10 | 20 | 51 | |
| Scorpius | The Scorpion | 24 | 10 | 20 | 44 | |
| Sagittarius | The Archer | 31 | 14 | 22 | 69 | |
| Capricornus | The Goat | 28 | 28 | 29 | 51 | |
| Aquarius | The Water-bearer | 45 | 41 | 47 | 108 | |
| Pisces | The Fishes | 38 | 36 | 39 | 113 | |
| Cetus | The Whale | 22 | 21 | 45 | 97 | |
| Orion | Orion | 38 | 42 | 62 | 78 | |
| Eridanus, Fluvius | Eridanus, the River | 34 | 10 | 27 | 84 | |
| Lepus | The Hare | 12 | 13 | 16 | 19 | |
| Canis major | The Great Dog | 29 | 13 | 21 | 31 | |
| Canis minor | The Little Dog | 2 | 2 | 13 | 14 | |
| Argo Navis | The Ship | 45 | 3 | 4 | 64 | |
| Hydra | The Hydra | 27 | 19 | 31 | 60 | |
| Crater | The Cup | 7 | 3 | 10 | 31 | |
| Corvus | The Crow | 7 | 4 | 9 | ||
| Centaurus | The Centaur | 37 | 35 | |||
| Lupus | The Wolf | 19 | 24 | |||
| Ara | The Altar | 7 | 9 | |||
| Corona Australis | The southern Crown | 13 | 12 | |||
| Pisces Australis | The southern Fish | 18 | 24 | |||
| Columba Noachi | Noah’s Dove | 10 |
| Robur Carolinum | The Royal Oak | 12 |
| Grus | The Crane | 13 |
| Phœnix | The Phenix | 13 |
| Indus | The Indian | 12 |
| Pavo | The Peacock | 14 |
| Apus, Avis Indica | The Bird of Paradise | 11 |
| Apis, Musca | The Bee or Fly | 4 |
| Chamæleon | The Chameleon | 10 |
| Triangulum Australis | The South Triangle | 5 |
| Piscis volans, Passer | The Flying Fish | 8 |
| Dorado, Xiphias | The Sword Fish | 6 |
| Toucan | The American Goose | 9 |
| Hydrus | The Water Snake | 10 |
| Hevelius. | Flamsteed. | ||
|---|---|---|---|
| Lynx | The Lynx | 19 | 44 |
| Leo minor | The Little Lion | 53 | |
| Asterion & Chara | The Greyhounds | 23 | 25 |
| Cerberus | Cerberus | 4 | |
| Vulpecula & Anser | The Fox and Goose | 27 | 35 |
| Scutum Sobieski | Sobieski’s Shield | 7 | |
| Lacerta | The Lizard | 10 | 16 |
| Camelopardalus | The Camelopard | 32 | 58 |
| Monoceros | The Unicorn | 19 | 31 |
| Sextans | The Sextant | 11 | 41 |
400. There is a remarkable track round the Heavens, called the Milky Way from its peculiar whiteness, which is owing to a great number of Stars scattered therein; none of which can be distinctly seen without telescopes. This track appears single in some parts, in others double.
401. There are several little whitish spots in the Heavens, which appear magnified, and more luminous when seen through telescopes; yet without any Stars in them. One of these is in Andromeda’s girdle, first observed A. D. 1612, by Simon Marius; and which has some whitish rays near its middle: it is liable to several changes, and is sometimes invisible. Another is near the Ecliptic, between the head and bow of Sagittarius: it is small, but very luminous. A third is on the back of the Centaur, which is too far South to be seen in Britain. A fourth, of a smaller size, is before Antinous’s right foot; having a Star in it, which makes it appear more bright. A fifth is in the Constellation of Hercules, between the Stars ζ and η, which spot, though but small, is visible to the bare eye if the sky be clear and the Moon absent.
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.
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.
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.
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].
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.
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 21⁄2 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.