LETTER XX. OF THE CONSTELLATIONS, AND THE PHENOMENA OF THE FIXED STARS. THE heavens are divided by astronomers into three regions, called the northern and southern hemispheres, and the zodiac; and in order that the fixed stars may be treated of according to their true positions and situations, they have been classed under the outlines of certain imaginary figures of birds, beasts and other animals; which are called Constellations. The number of these, in the northern hemisphere, is thirty-six; in the southern thirty-two; and in the zodiac twelve: and as there are some stars that admit of no regular arrangement, they are called unformed stars; and others, from their cloudy appearance, are comprised under the name of Nebulæ. This division of the starry firmament into Constellations, is of the highest antiquity. Bootes and the Bear are spoken of both by Homer and Hesiod; Arcturus, Orion, and the Pleiades, are mentioned in the book of Job; and there is scarcely any ancient author in which the names of some of the most remarkable ones are not to be found. But to trace the origin of this invention, and to show why one animal had the honour of being advanced to heaven in preference to another, is no easy task. M. Fréret, the Abbe la Pluche, and several other writers of considerable eminence, have ransacked all the legends of fabulous history for the illustration of this subject; but, except in a few obvious instances, no consistent and satisfactory account has yet been given. Most of the memorable events and customs of ancient times were involved in obscure hieroglyphical representations; and many of the constellations are probably symbols of this kind. The division of the zodiac into twelve signs, of thirty degrees each, has a manifest relation to the twelve months of the year; and the animals, by which. those signs are denoted, were perhaps designed as emblems of the different productions of nature, in those seasons over which they preside; or as indicating certain circumstances relating to the motion of the sun in the heavens. Many of the constellations also appear to have been formed in honour of certain heroes and celebrated personages, whose memory they were meant to perpetuate; and any vague resemblance of a crown, a cross, or a triangle, would occasion the parts of the heavens where they were found to be called by those names. This manner of classing the stars is indeed so natural, that it is found among the Chinese, the Americans, and many other nations that seem to have had no intercourse with the rest of the world. The heavens being thus divided, it was more easy to reduce the stars into order, and to determine their number, than it would have been without such a contrivance. And though this be considered, by the uninstructed part of mankind, as an impossible thing, it has been often attempted both by the ancients and moderns. Hipparchus the Rhodian, who lived about 120 years before Christ, was the first among the Greeks that engaged in this singular enterprize; "daring (according to Pliny) to undertake a thing which seemed to surpass the power of a divinity; that is, to number the stars, and to ascertain their true places in the heavens." It was imagined in those days, as it is at present, that, in a fine winter's night, when the sky is perfectly clear, the stars which may be seen in the firmament are beyond the reach of all calculation; and that "To count their numbers, were to count the sands ARMSTRONG. This, however, is a mistaken notion: the number of stars, as I have observed in a former letter, that can be seen by the naked eye in the whole visible hemisphere, is not much above a thousand. Hipparchus, from his own observations, and those of the ancients that preceded him, inserted in his catalogue only one thousand and twenty-two, 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. But of all the catalogues of the stars which have hitherto been made, that which is given by Flamsteed, in his Historia Coelestis, and the one lately published by Bode, are the most complete. The number of stars inserted in the former of these catalogues is about three thousand; which number has been since aug. mented to near five thousand, by Halley, La Caille, Le Monnier, and others; and from the accuracy of their observations, there is scarcely a star to be seen in the heavens, whose place and situation is not better known than that of most cities and towns upon the earth. And in order that the memory may not be burthened with a multiplicity of names, astronomers mark the stars of every constellation with a letter of the Greek alphabet; denoting those that are the most conspicuous by a, the next by 6, and so on in succession; by which means they can be spoken of with as much ease as if cach had a separate name. This was the invention of John Bayer, a native of Augsburg, in Germany, who first introduced it about the year 1603, in his charts of the constellations. But the best works of this kind, that have yet been executed for representing the constellations, and the stars of which they are composed, are the Atlas Cœlestis of Flamsteed, and Bode's Atlas before-mentioned; which, together with the stars discovered by La Caille in the southern hemisphere, contain an entire map of the heavens; so that by means of these charts, or a good celestial globe, we can easily know any particular star which is discernible to the eye, and tell the constellation to which it belongs. The names of the constellations, and the manner of denoting some of the principal stars of the first and second magnitude, may be seen in the follow |