CHAPTER II.

Of the fixed stars-division of the stars into constel

lations, &c.

1. Those celestial bodies, which have always been observed to keep the same relative distances with regard to each other, are called fixed stars, or simply stars.

From continued observations on the heavens, in clear nights, we shall soon see that the fixed stars constitute by far the greater number of the celestial bodies. It will likewise follow that they do not appear to have any proper motion of their own; but that the several apparent motions of the fixed stars are really caused by the diurnal motion of the earth, the precession of the equinoxes, properly called the recession of the equinoctial points, the aberration of light, &c. For, the apparent diurnal motion of all the heavenly bodies from east to west, is caused by the real motion of the earth on its axis, in a contrary direction; and the recession of the equinoctial points, will cause the fixed stars to have an apparent motion backwards from west to east, in circles parallel to the ecliptic, at the rate of 50" nearly in a year: in consequence of this motion, the longitude of the stars will be always increasing; their latitude remaining the same, because it is found by observation, that the equinoctial moves on the ecliptic, contrary to the order of the signs, while the ecliptic keeps nearly the same position in the heavens. The nutation of the earth's axis, the aberration of light, &c., cause some small change in the places of the stars. There are other changes in the apparent magnitude, lustre, &c. of the fixed stars, which shall be considered in a subsequent part of this work.

2. Those celestial bodies that are constantly changing their places, as well with regard to the fixed stars as to one another, are called planets, or wandering stars.

1

A planet may be known from a fixed star, by the steadiness of its light; for a fixed star appears to emit a twinkling light, but a planet gives a mild steady light. The planets, besides their apparent diurnal motions, have apparent motions that at first seem not easily brought under any general laws. Sometimes they appear to move in the same direction in the heavens as the sun and moon; at other times in a contrary direction; and sometimes they appear nearly stationary, or fixed in the same point of the heavens.

There are ten planets, whose names are, Mercury, Venus, Mars, Ceres, Pallas, Juno, Vesta, Jupiter, Saturn, and Uranus. Five of these planets have been observed from the remotest antiquity; the other five, lately discovered, are only visible by the assistance of telescopes. 'The motions, magnitudes, distances, &c. of the planets, shall be fully considered in the next book.

3. The fixed stars are divided into orders or classes, according to their apparent magnitudes. Those stars 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 naked eye. All those stars which cannot be seen without the aid of a telescope, are distinguished by the name of telescopic stars.

The stars of each class are not all of the same apparent magnitude; there being considerable difference in this respect; and those of the first magnitude appear almost all different in lustre and size. There are also others of intermediate magnitudes, which astronomers cannot refer to one class in preference to another, and therefore they place them between the two. For instance, in M. Laland's catalogue of 600 principal stars visible at Paris, and which contains none less than of the fifth magnitude, there are no fewer than 126 stars of intermediate magnitudes. So that instead of six magnitudes, we may say that there are almost as many orders of stars as there are stars; such considerable varieties being observable in their magnitude, colour, brightness, &c. Whether these varieties of appearance are owing to a diversity in their real magnitude, or from their different distances, is impossible to determine; but it is highly probable that both of these causes contribute to produce those effects.

4. The number of stars visible to the naked eye in both hemispheres, is not more than 2000; but to whatever part of the heavens a telescope is directed, multitudes of stars appear, which were before invisible. The number of stars that can be seen by the naked eye in the whole visible hemisphere, is not more than 1000.

The reason why they appear so innumerable, on casting the eye quickly to the heavens in clear winter nights, arises from our sight being deceived by their twinkling, and from our viewing them confusedly, and not reducing them to any order. Different astronomers have given catalogues of the fixed stars, disposed according to some order, in their several constellations; with the right ascension, declination, longitude, latitude, &c. of each; and from the accuracy of their observations, there is scarcely a star to be seen in the heavens, whose place is not better known than that of most towns upon the earth.

Hipparchus, who first undertook to make a catalogue of the fixed stars, from his own observations, and those of the ancients that preceded him, inserted in his catalogue only 1022 stars, annexing to each of them the latitude and longitude which they had at that time.

Ptolemy added four to this number; and others were afterwards discovered by different astronomers who applied themselves to this subject.

Tycho Brahe determined the places of 777 stars, for the end of the year 1600; Kepler from the observations of Tycho, afterwards increased this number to 1000, in the Rhudolphine tables. Dr. Halley made a catalogue of 350 stars not visible above the horizon of London.

De la Caille, at the Cape of Good Hope, in the year 1751 and 1752, made accurate observations of about 10,000 stars, near the south pole; the catalogue of which was published in the Memoirs of the French Academy of Sciences, for the year 1752. Bayer and John Hevelius, also published catalogues of the stars, and Flamstead, in his Historia Cælestis, published a most complete catalogue of more than 3000 stars, observed by himself.

In 1782, M. Bode, of Berlin, published a very extensive catalogue of 5058 of the fixed stars, collected from the observations of Flamstead, Bradley, Hevelius, Mayer, La Caille, Messier, Monnier, D'Arquier, and several other astronomers, all rectified to the beginning of 1780; and accompanied with a celestial atlas of the constellations, engraved in a most delicate and beautiful manner.

M. Laland has published a new catalogue of more than 12,000 stars. Almost all of which has not been before observed.

But the most surprising list that has ever been formed of the fixed stars, is the catalogue by M. F. Laland, in which are determined the places of 50,000 stars from the pole to 2 or 3 degress below the tropic of capricorn.

The telescope opens an extensive field to the contempla tive mind. By its aid we are enabled to discover myriads of stars which before were invisible to the unassisted eye; as we increase the power of the instrument, more and more stars are brought into view, so that their numbers may be considered infinite. Many of the stars that appear single to the naked eye, are by the telescope found to be double, treble, &c., or to consist of several stars very near each other; of these, several have been observed by Cassini, Hooke, Long, Maskelyne, Hornsby, Pigott, Mayer, &c.; but Dr. Herschel has been by far the most successful in observations of this kind. He has already formed a catalogue containing 269 double stars, 227 of which have not been noticed by any other person. Among these there are also some stars that are treble, quadruple, and multiple.

5. The ancient poets, referring the rising and setting of the stars to that of the sun, make three kinds of rising and setting; namely, cosmical, achronical, and heliacal.

These are called the poetical rising and setting of the stars, because they are mostly taken notice of by the ancient poets; formerly they served to distinguish particular seasons of the year; but they are now chiefly useful in comparing and understanding passages in the ancient writers.

6. The cosmical rising and setting of a star, is, when the star rises with the sun, or sets when the sun rises.

7. The achronical rising and setting of a star, is, when the star sets with the sun, or rises when the sun sets.

8. The heliacal rising and setting of a star, 1s, when the star first becomes visible in the morning, after having been so near the sun as to be hidden by the splendour of his rays; or when the star becomes invisible in the evening on account of its nearness to the sun.

9. An imaginary zone or belt in the heavens, which extends about 8 degrees on each side of the ecliptic, is usually called the zodiac.....

The zodiac includes the paths of all the planets among the fixed stars, except Ceres and Pallas, which have been discovered since the year 1800.

(

e

The zodiac appears to be very ancient, and to have passed from the ancient Hindoos, successively westward, through Persia, Arabia, Assyria, Egypt, &c. to Europe; as speci- speci mens of the same kind of zodiac have been found in all those countries with only some variation in the figures of some of the constellations; accompanied also with appropriate emblematical figures of the sun and moon, with those of the planets in their order.

10. In order to distinguish the fixed stars from each other, the ancients classed them under the outlines of certain imaginary figures of men, birds, fishes, &c. called constellations or asterisms. Those stars which were not included in the ancient constellations, were called unformed stars; but on the modern celestial globes, the constellations are made to include all the unformed stars.

The constellations are called after the names of those figures under which they are represented. See the tables at the end of this chapter. In what age of the world this arrangement of the stars into constellations took place, is not known; but it was certainly antecedent to any authentic record; so that whether the shepherd or the sage was employed in their formation, cannot now be ascertained. Bootes and the Bear are spoken of both by Homer and Hesiod; Arcturus, Orion, and the Pleiades, are mentioned in the book of Job; the writer of the book of Amos has also mentioned Orion and the seven stars; and there is scarcely any ancient