are so arranged for convenience of description. The first astronomers, in order to estimate better the apparent motion of the sun, referred it to those constellations through which it appeared to pass, and which are 12 in number. They are, in Latin, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius Capricornus, Aquarius and Pisces. Th zone, or band, which contains them, is called the zodiac (q. v.), and each constellation is called a sign of the zodiac. In consequence of a motion of the earth's axis, the constellations no longer correspond to the same points of the orbit; but as we confine the name signs to the 12 divisions of the circumference of the circle, which measures the whole revolution of the earth, and as these divisions do not change, the vernal equinox always corresponds to the first point of the sign Aries, the summer solstice to the first point of the sign Cancer, the autumnal equinox to that of Libra, and the winter solstice to that of Capricorn, although the constellations, which bear these names, have ceased to be connected with these seasons. (See Precession of the Equinoxes.) To penetrate yet farther into the heavens, it is necessary to aid the imperfection of vision by the telescope, which discovers to us millions of stars in the infinity of space. In a clear night, turn your eyes to the irregular zone of whitish revolve in regular but unequal periods,turning at the same time on their axes. Their number now known is 11. We mention them in the order of their distances from the sun-Mercury, Venus, Earth, Mars, Vesta, Juno, Ceres, Pallas, Jupiter, Saturn, and Uranus, or Herschel. Five of these are visible to the naked eye, and were known to the ancients; five have been discovered in modern times by the aid of the telescope. Some of these bodies have smaller ones in their neighborhood, which revolve round them at the same time that they accompany them in their orbits of revolution round the sun, and turn on their own axes. The former are called primary, to distinguish them from these attendants, which are called the secondary planets, or satellites. The latter are opaque, like the former. The earth is accompanied by one, which is called the moon, Jupiter by four, Saturn by seven, with his remarkable ring, and Herschel by six. The interposition of one of the planets between the sun and an observer stationed on another planet, produces an eclipse. (q. v.) From time to time, small specks appear in the heavens, of a feeble lustre, moving slowly in the midst of the other stars. Gradually, as they approach nearer, their velocity increases; their light is more brilliant; and, after passing into the immediate vicinity of the earth and sun, they recede again, and disappear in the distance. These are called comets (which signifies hairy light: it is the milky way (q. v.): you will bodies) from the peculiar luminous train by which they are attended, and which the ancients called hair, and the moderns, rail. These bodies, long the objects of error to man, as the harbingers of pestilence and war, are now known to be subject to the common laws of nature, and to revolve round the sun in regular periods. The sun, the 11 primary and 18 secondary planets, and the comets, constitute the solar system. Far beyond these limits, at an immeasurable distance, lie the fixed stars, infinite in number, of a brilliant lustre, and constantly changing color. Their distance, and the brilliancy of their light, with the fact that their magnitudes remain always the same, render it probable that they are luminous bodies, like so many suns. They have been formed into groups of arbitrary extent, under the names of gods, men, beasts, &c., which are called constellations. Of these the ancients knew 48; the moderns have increased the number to more than 100. It should be understood, that the stars, thus grouped together under one name, have no connexion with each other, but 37 VOL. I. find it to consist of an infinite number of stars, whose inconceivable distance renders their light too feeble to make a distinct impression on the naked eye. Continue your examination, and you will observe luminous spots of an undefined shape: these are nebula, some of which a further observation will show you to be assemblages of stars, like the milky way, while others will appear to consist of an unbroken mass of whitish light. You will find, also, some stars to be variable, undergoing a periodical change of brightness: some, which appear single to the naked eye, will be found to be double, triple, &c., and to revolve round a common centre of gravity by twos, threes, &c. Compare your observations with those of your predecessors, and you will find that new stars have appeared at different times, and afterwards disappeared, and that others have experienced a change in the intensity of their light. Of the actual magnitude and distance of the stars we know nothing. The diameter of the earth's orbit is 200,000,000 miles; yet we can detect no difference in their ap 434 us. ASTRONOMY-HISTORY OF ASTRONOMY. parent places, viewed from the opposite points of this diameter: a change of place amounting only to a second would be detected by the accuracy of modern observations: geometrical considerations, therefore, prove that the nearest star cannot be less than 20 billions of miles distant from After considering the apparent motions of the heavenly bodies, and the real motions which give rise to these appearances, physical astronomy rises to the explanation of the cause, and the investigation of the laws, of the celestial phenomena. Applying the laws of motion to the heavenly bodies, it discovers a force operating throughout, which is called attraction, the amount of which is directly as the quantity of matter, and inversely as the squares of the distances. By the application of this general principle, it descends to those more refined inequalities, which, owing to their minuteness, or the length of their periods, would escape or mislead the observer unassisted by theory. ASTRONOMY, history of. The history of this science begins with the most remote antiquity. The starry heavens must have been one of the first and most striking objects which attracted the attention of man, and his immediate wants compelled him to attend to the revolution of the seasons, the changes of the moon, &c. The most ancient astronomical observations known to us are Chinese. Such a one, mentioned by Montucla (see p. 455 of his work, vol. 1, quoted below), viz., a conjunction of Saturn, Jupiter, Mars, Mercury and the moon, occurs almost 2500 years before our æra. The Chaldeans also boast of some very ancient astronomical observations, but Ptolemy (q. v.) only mentions two lunar eclipses observed by them, about 700 B. C. Still less importance does he ascribe to the astronomical knowledge of the Egyptians, although the placing of their pyramids in a position exactly facing the four cardinal points of the compass, the zodiacs discovered in Egypt (see Zodiac), and other circumstances, are by no means calculated to give us such a disadvantageous idea of it. The theory of Bailly, a later historian of astronomy, respecting a nation settled in Middle Asia, and possessed of profound astronomical knowledge, seems as unfounded as our acquaintance with Indian astronomy is slight. The science made greater progress in Greece, and the Greek philosopher Thales (q. v.), born 640 B. C., calculated a solar eclipse. Pythagoras, also, seems to have been possessed of astro nomical knowledge. After him, the Athe nian Meton (433 B. C.) introduced the famous lunar cycle of 19 years, at the end of which time the new moon appears on the same day of the year as at the beginning of it, since 19 solar years constitute very nearly 235 lunations-a discovery which was then regarded as so important, that the calculation was engraved in letters of gold, whence the number, which marks the year of the cycle, is still called golden. Great progress was made in astronomy under the Ptolemies, and we find Timocharis and Aristyllus employed, about 300 years B. C., in making useful planetary observations. But they were far surpassed, in philosophical spirit, by Aristarchus (q. v.) of Samos, born 267 years B. C., who, according to the indubitable evidence of Archimedes (see the remarkable passage in the beginning of Avenarius), taught the double motion of the earth around its axis and around the sun;* and, about 100 years after him, Hipparchus (q. v.) determined more exactly the length of the solar year, the eccentricity of the sun's orbit, the precession of the equinoxes, and even undertook a catalogue of the fixed stars; ausus, às Pliny (Hist. Natur., lib. 2, cap. 26) expresses himself, rem etiam Deo improbam, annumerare posteris stellas, cœlo in hereditatem cunctis relicto. From the time of Hipparchus, a chasm exists in the history of astronomy, till the commencement of the 2d century after Christ, when Ptolemy (q. v.) compiled a complete system of astronomy, in 13 books, which is best known under the name of Almagest, given it by the Arabians, who translated it into their language in 827, and which, as the Ptolemæan system of the world, notwithstanding its many errors, exposed in the article Universe, system of the, in this work, has maintained its value down to the latest times. Among the Romans, on the contrary, astronomy was never much esteemed; and no astronomical discovery had its origin with them; though it must be observed, that expressions occur in Seneca's Quæstiones Nat., vii. 13, respecting comets, which are worthy of a riper age; and * Aristarchus says expressly, 1st c., that the earth revolves in an oblique circle around the sun, and that the distance of the fixed stars is so great, that this circle can only be considered as a point in comparison; but he seems to have come to this conclusion, not as an astronomer, but as a Pythagorean, regarding fire (the sun) as the centre of the universe.-We take this occasion to correct the common but erroneous opinion, that Copernicus was sage of Avenarius, as this book was not printed indebted, for his system of the world, to this pastill after his time. the service likewise deserves mention, which Julius Cæsar rendered, by his correction of the calendar, the details of which may be found in the article Calendar. But, with the irruption of the barbarians on one side, and the destruction of the Alexandrian library on the other, such a total stagnation occurred in the case of astronomy, as in that of the sciences in general, that we find no traces of astronomical study and observation, till the 9th century, among the Arabs, whose translation of Ptolemy's works has already been mentioned. Of their astronomers, the caliph Almamon and the princes Albategni and Thebith deserve to be named. Among the Moors who invaded Spain, there were Arabic scholars, who transplanted the science to that country. With the Mohammedan faith, Arabic learning was likewise introduced into Persia, the reigning prince of which, Ulug-Beigh, in the beginning of the 15th century, collected, at his capital, Samarcand, an assemblage of the most famous living astronomers. But we must not overrate the merits of the Arabian astronomers, since they confined themselves entirely to the system of Ptolemy, and confounded the science with the dreams of astrology; though, on the other hand, the benefits which they have rendered by valuable observations of the fixed stars (many of which, it is well known, still bear Arabic names), of eclipses, of the obliquity of the ecliptic (q. v.) &c., and by the preservation of ancient mathematical works, which have come to us in their translations, are not to be forgotten. Among the Christian nations, during this time, a deep ignorance generally prevailed, but the cultivation of the astronomical sciences was not entirely neglected. Thus the emperor Frederic II, who died in 1250, caused the Almagest (the Greek original being no longer extant) to be translated from the Arabic into Latin; and king Alphonso of Castile, about the same time, invited to his court several astronomers, and commissioned them to prepare a set of new astronomical tables, which, under the name of Alphonsine tables, have acquired much celebrity, but, in the 17th century, differed a whole degree from the true situation of the celestial bodies. We pass over several less famous names, in order to introduce those of the German astronomer and mathematician, George of Peurbach or Purbach, born in the Austrian dominions, in 1423, who published various valuable astronomical tables, such as the table of sines, from 10 to 10', and a still more famous scholar, John Müller, born at Königsberg, in Franconia, and thence called Regiomontanus, from whom we possess the first good and complete Ephemerides. After him, a brighter light was shed over astronomy by Nicholas Copernicus (q. v.), born in 1473, who gave the science an entirely different aspect, exploded the Ptolemæan hypothesis, and, in its stead, substituted the Copernican system of the world, which, with a few modifications, is still prevalent, and universally acknowledged to be correct. He it was that gave the sun its place in the centre of the planetary system; who first conceived the bold idea, that the earth is a planet, like Mercury, Venus, and the rest, and moves, in common with them, in a circle around the sun; and who maintained that these circles (or, in conformity with subsequent corrections, these orbits, differing but little from circles) were sufficient to explain the most complicated motions of the other planets, and even their apparent cessations of motion and retrogradations, which had hitherto baffled all conjecture. How much freedom of spirit was required thus to rise superior to the prejudices of centuries, we are almost incompetent to judge, now that the truth of the system is settled; but his great countryman, Kepler, has depicted the spirit of the man, by a few energetic strokes, calling him virum maximo ingenio et quod in hoc exercitio magni momenti est, animo libero. His system did not, however, meet, immediately, with a general reception; and, while Rheticus and others were its advocates, some distinguished astronomers made objections to it, among which the imperceptibleness of any annual parallax of the fixed stars, which it seemed must necessarily result from the motion of the earth, was the one of most weight. The most distinguished of these opponents of the great Copernicus was Tycho Brahe (q. v.), born in Denmark, in 1546. He maintained that the earth is immovable, in the centre of the universe; that the whole heavens turn around it in twenty-four hours; that the moon, and also the sun, by virtue of their own motions, describe circles around the earth, while Mercury, and the other planets describe epicycles around the sun. (See Epicycle.) The principal authority that Tycho adduced in support of this opinion was, the literal sense of various passages of the Bible, where a total absence of motion is ascribed to the earth; but, although he did much injury to science by supporting this erro 436 HISTORY OF ASTRONOMY. neous opinion, we are under infinite obligation to him for the great exactness of his observations, which opened to his pupil and assistant, Kepler (q. v.) of Wurtemburg (born 1571, died 1631), the way to the more accurate discovery of the form of the celestial orbits, and the true theory of the planets; for only eight minutes' difference between the position of the planet Mars, as calculated on the hypothesis of the circle, and its actual position, as observed by Tycho, gave this sagacious astronomer occasion, as he expresses himself, in p. 114 of his Astronomia,* * "ad totam astronomiam reformandam," since he derived from it the elliptical forms of the orbits of the planets (differing, however, but little from the circles of Copernicus), the sun being situated in one of the foci of the ellipse. Advancing in his glorious course, Kepler, moreover, demonstrated that, in each elliptical revolution of the planets around the sun, an imaginary straight line, drawn from the latter to the former (the radius vector), always describes equal areas in equal times; and, lastly, that, in the revolutions of the planets and satellites, the squares of the times of revolution are as the cubes of the mean distances from the larger body. These three important truths are comprehended under the name of Kepler's laws. About the same time, Galileo (q. v.), who died in 1642, accomplished another step towards the more accurate investigation of celestial meckanics, by his discovery of the laws of the descent of heavy bodies; and, although the Catholic church compelled this philosopher to abjure as heretical the doctrine which he had publicly promulgated respecting the motion of the earth, to which he had been led by his observations of the other celestial motions, made by means of the telescope, then first invented, this attempt to obstruct the march of intellectual improvement only served to show the impotency of such persecutions. In the first 10 years of the 17th *The title of this immortal work, containing the code of theoretical astronomy, is, Astronomia nova, 'ALTIOλOYNTOs, seu Physica Coelestis tradita Commentariis de Motibus Stella Martis, ex Observationibus Tychonis Brahe, Jussu et Sumptibus Rudolphi II, Romanorum Imperatoris, etc., plurium Annorum pertinaci Studio elaborata, Praga, a S. C. M. Muthematico Joanne Keplero (1609, fol.). These persecutions have, nevertheless, been very recently repeated, and the public papers have related the following anecdote: About the beginning of the year 1820, the professor of astronomy at the academy della sapienza at Rome, signor Settele, submitted the manuscript of his astronomical lectures to the appointed authorities, soliciting per century, there appeared, in Dantzic, Hevelius, who was distinguished for his observations of Mars; in France, Cassini, whose exertions in most of the branches of astronomy were highly successful, and who transmitted his industry and his energy to a son, grandson and great-grandson; and in Holland, Huygens, the famous inventer of the pendulum, and the precursor of the immortal Newton, in his investigations respecting celestial mechanics. Newton himself (q. v.), born in 1642, was engaged till a short time before his death, 1727, in producing an entire revolution in physical astronomy (see the preceding article), while, by his Principia Mathematica Philosophic Naturalis, he became the lawgiver of celestial mechanics, as Kepler had been of theoretical astronomy, by means of his Astronomia. Descartes had sought the cause of the motion of the planets around the sun, and of the satellites around the planets, in the rotatory motion of a subtile matter. Newton felt the defects of this hypothesis, and proved, with the superiority of true genius, that the elliptical motion of the planets was caused by the combined action of the attractive power exerting a force in the inverse ratio of the squares of the distances, and of an impulse originally communicated to the planets, which impulse, as may be demonstrated, continues for ever in empty space. With Newton the laws of the heavenly bodies were completed, and he and Kepler have left to later times merely the developement of the truths which they established. By the application of their principles, several succeeding astronomers have gained a high reputation; e. g., Halley, by his theory of comets; Bouguer and Maupertius, by their exertions to determine the form of the earth; their countryman de la Caille, by improving the doctrine of refraction; the great German astronomer Tobias Mayer, by his lunar tables; Bradley, by the discovery of the aberration of light; also de l'Isle, Lambert, Euler and others. (q. v.) mission to print them. This was refused, "because he defended the motion of the earth around the sun"-a doctrine condemned by the Roman court, as contrary to the Bible, and which had already involved the immortal Galileo in the disgrace of recantation. Not discouraged by this, Settele applied to the inquisition, with the request that it would give an explanation of its own, adapted to the present state of science. The inquisition was silenced; permission was granted to print the book; but Settele was ordered to add in a note, "in conformity with truth," that the persecutions which Galileo had suffered were to be imputed not so much to his system as to the improper language used by him. This, however, is notoriously false. In more recent times, Laplace, by his Mécanique Céleste, and Gauss, by his Theoria Motus Corporum Cœlestium, have completed the structure of Newton; while Zach, Lalande, Maskelyne, Bessel, Olbers, Piazzi, Encke, Delambre, Biot, Arago, Mechain, Herschel, &c., have enlarged, on all sides, the territory of the science. Thus Herschel's discovery of the planet Uranus and its moons, in 1781; Schröter's efforts to obtain a knowledge of the surface of our moon and of Venus; Piazzi's discovery of Ceres, in 1801; Olbers' discovery of Pallas, in 1803, and of Vesta, in 1807; Harding's discovery of Juno, in 1804; Olbers' and Encke's computation of the orbits of two comets; the recent measurements of a degree in France, England, Germany, Sweden; the perfection which has been given to astronomical instruments, by Ramsden, Troughton, Reichenbach, &c., are well known; and the combined industry of so many living astronomers allows us to hope for no less splendid results in the advancing improvement of astronomy.-On the advantages of this science, it can scarcely be necessary to dwell. "It need but be mentioned," says Gehler, "to excite emotions of grandeur; and the idea which it gives us of the immensity of the universe, and the power, wisdom and goodness of its almighty Author, must inspire men of the coldest feelings with sentiments of admiration. It is not necessary for us to point out the benefits which accrue from it to the human race, by enabling them to divide and observe the flight of time; its use in navigation, the determination of the situation of places on the earth, &c." By the aid which it affords to navigation, it exercises no small influence in the general improvement of the human condition. This science, moreover, unites the strictness of mathematical reasoning with an exalted feeling for the sublime and beautiful, and fills the mind both with confidence in itself, from its ability to calcalate with certainty the career of distant worlds, and with a becoming humility in reflecting how small a part of the universe is our earth, and how brief its known duration, compared with the immense periods which enter into the calculations of astronomy. Young says, An undevout astronomer is mad. There have been, however, several astronomers who believed in no God; being led, by the contemplation of the necessary laws of the heavenly bodies, to the belief ' in a general, universal necessity.-German literature contains a great number of popular works on astronomy, of which several are designed for ladies. Of the numerous works on astronomy, we shall only mention here the latest and most important manuals and elementary works: Astronomie par de Lalande, 3d ed., Paris, 1792, 3 vols., 4to. (there is an abridgment of it-Abrége d'Astronomie par de Lalande, Paris, 1795); Astronomie Theorique et Pratique, par Delambre, Paris, 1814, 3 vols., 4to.-a work important for professional astronomers; Schubert's Theoretical Astronomy, Petersburg, 1798, 3 vols., 4to., and the new French edition of the same work, 1822; Biot's Traité Élémentaire d'Astronomie Physique, 2d ed., Paris, 1810, 3 vols.; Laplace's Exposition du Système du Monde, 5th ed., Paris, 1824 (a general exposition of the results developed in the large work, Mécanique Céleste); Bode's Illustrations of Astronomy (which is confined to the less difficult propositions of geometry and astronomy) 3d ed., Berlin, 1808, 2 vols.: together with this work, we may mention Bürjas' Manual of Astronomy, Berlin, 1794, 5 vols., which requires, however, more extensive knowledge. Excellent, though very condensed, is Bohnenberger's Astronomy, Tübingen, 1811. Piazzi's Italian Manual of Astronomy is a good work. Among the English treatises are Woodhouse's Elementary Treatise on Astronomy, 1823, and Ferguson's Lectures on Astronomy, a popular work; also Vince's Complete System of Astronomy, 3 vols., 4to., with additions, 1814. To astronomers, practical and theoretical, Bessel's Observations at the Observatory of Königsberg, which have appeared in folio since 1813, are indispensable. Notices of astronomical tables may be found in the larger astronomical treatises mentioned. With respect to astronomical periodicals, Zach's Monatl. Correspondenz zur Beförderung der Erd- und HimmelsKunde, with which is connected Lindenau's and Bohnenberger's Astronom. Zeitschr., is continued under the title Correspondence Astronomique, Géographique, &c. du baron de Zach. Schumacher has also published, in Copenhagen, since 1822, Astronomische Nachrichten. The latest observations may be also found in the Paris Connaissance des Tems, and in the Berlin Astronomisches Jahrbuch, which has been published for more than 50 years. The history of astronomy may be found at large in Montucla's already mentioned Histoire des Mathématiques, 4 vols., 4to.; in Delambre's Histoire de l'Astrono mie Ancienne, celle du Moyen Age et Mod erne, Paris, 1817, 5 vols. 4to.; and in Bail |