RECENT DISCOVERIES IN ASTRONOMY, RELATING TO THE PLANETS AND SATELLITES OF THE SOLAR SYSTEM. By Professor J. Lovering of Harvard University. ASTRONOMERS have designated by the various names of small planets, planetoids, asteroids, or extrazodiacal planets, the cluster of singular bodies situated in that shell of the solar system which is bounded on the outside by the orbit of Jupiter, and on the side nearest the sun by Mars's orbit. Captain Smyth, in his "Cycle of Celestial Objects,"* thus introduces his account of the four members of this group whose almost simultaneous discovery heralded the present century, and which had received no reinforcement up to the year (1844) when his work was published. "Quitting Mars, we now arrive at a singular family of small bodies, recently discovered, the history of which forms a planetary episode of no common interest, whether considered as a general astronomical gain, or a glory to the speculative fancy and untiring diligence of the scientific Germans, to whom the world is chiefly indebted for them." This author might with propriety call this discovery a recent one, although it occurred nearly half a century previous to the date at which he was writing; for Ceres, Pallas, Juno, and Vesta were at that time the only planets, with the exception of Uranus (discovered in 1781), whose early astronomical history was not lost in their high antiquity. But since 1844, the number of planets known to astronomers has doubled. More rapidly even than the stars have multiplied on the flag of our political Union have new planets eagerly crowded into the republic of science. In the region first settled about half a century since by four small planets, and where only six years ago there were known to exist no others, now circulate fifteen sovereign planets. Simultaneously with this growth in the interior of the solar system, the annexation of the lone står of Neptune has pushed forward its extreme outposts ten hundred millions of miles. The names of the new planets and of their discoverers, which are best given in a tabular form with other facts of history concerning them and their elements of motion, will show that there are now living more than one astronomer to inherit from Olbers the epithet of the "fortunate Columbus of the heavens." In a letter to Schumacher, dated October 12, 1847, Sir J. F. W. Herschel speaks thus of the nomenclature adopted for the small planets already discovered. "Pallas, Juno, Ceres, and Vesta, as sober and majestic duennas, will abundantly provide for the respectability of the group between Mars and Jupiter, while Astræa, Iris, Hebe, and Flora will attract all eyes and fill all imaginations with sweet and graceful images." t The following table contains the names of all the modern planets, except the last discovered, which is nameless at this time, ‡ the date and place of the discovery, and the name of the discoverer; also the apparent brightness of the planetoids. * I. 152. ↑ Astronomische Nachrichten, XXVI. 254. * Oct. 1, 1851. Kepler, Maclaurin, Lambert, || Wurm, and Kant all speculated on the arrangements in the solar system, and the probability that other planets existed not yet known to astronomy. In the first work which he published Kepler suggested the idea that a strange planet circulated between Mars and Jupiter.¶ Bode, in his well-known law, which he derived, as he himself says, ** from Titius of Wittemberg (to whom Voiron and Lalande distinctly ascribe the law ff), gave new life and distinctness to this idea, and the Baron de Zach went so far as to calculate, in 1784 -5, the orbit of the ideal planet, the elements of which he published in the Berlin Almanac for 1789. In 1800, six astronomers, of whom the Baron was one, assembled at Lilienthal and formed an association of twenty-four observers, the principal object of which was to force this planet from the region of analogy into the realm of sense. Schroeter was the president and Zach the perpetual secretary of this association. "Ere they had well got into harness," Piazzi discovered Ceres. After another year Olbers brought in Pallas, of which Captain Smyth says, "With all my coaxing I never raised a disk, as I could readily do with Ceres." Juno and Vesta followed, at intervals of a few years. As the search continued fruitless for nearly ten years after the discovery of Vesta, it was fairly concluded that this region of space was exhausted. At the close of the year 1845 the game was started again, and in this second heat a shorter time sufficed to capture eleven new planets, than was required, * Harding was soon after appointed Director of the Göttingen Observatory. † Markree Castle, Ireland. 1 Seen by Gasparis, May 23. § Astr. Nachr., XXXIII. 31. Lettres Cosmologiques, 1761 (p. 51 of edition of 1801). ¶ Humboldt's Cosmos, 711. ** Kentniss des Gestirnten Himmels, 7th edit., pp. 38, 55, 599. tt Voiron, Histoire de l'Astronomie, pp. 69, 70. Lalande, Bibliographie, 845. at the beginning of the century, to secure four. There are few fields of which the gleanings are so much fairer than the early harvest. But we should not forget that the four planetoids which first surrendered to the astronomer do not fall below the eighth magnitude, and Vesta comes up even to the sixth; whereas the second-comers do not surpass the ninth or tenth magnitude. During the last half-century, astronomy has surely made great progress, in the increased number of its cultivators, in the division of labor which they carry into their scientific pursuits, and in the more refined instruments with which they make their observations. The following remark of Delambre* is unfavorable to the expectation of finding any of the newly discovered planets registered as stars in the catalogues : that, "during the two years he was examining the right ascension of all the stars in all the catalogues, he never perceived an unknown star of the ninth or tenth magnitude without giving it the chase." It may not be out of place to say, that the "Monatliche Correspondenz," published by Zach from 1800 to 1813, was the organ of the astronomical association to which the world owes the discovery of the first four planetoids. Lindenau asks, “What would have been the fate of the small planets, if the 'Monatliche Correspondenz' had not then existed?" So important was this intelligencer, that astronomers of every kindred and tongue were compelled to learn the German language in order to read it. It should also be remembered to the credit of Zach, that, when Ceres had been lost to sight, he discovered it again on the last day of the same year that witnessed its first appearance. Olbers also rediscovered it, but not until the first day of the new year. Of the two names, Clio and Victoria, proposed by Mr. Hind for the planet discovered by him on the 13th of September, 1850, most of the American astronomers prefer the first. The names of individuals, whether those of the discoverers themselves, or of their sovereigns and patrons, have been banished by common consent from the nomenclature of planets. Herschel, Piazzi, and Leverrier, the Georgium Sidus, and the Sidus Ferdinandeum, the Medicean Stars, Sidera Brandenburgica, and Sidera Lodoicea, have not been able to maintain their title to Uranus, Ceres, and Neptune, to the satellites of Jupiter, or those of Saturn which Cassini discovered under the auspices of Louis the Fourteenth. The claims of Victoria on classical grounds are unsatisfactory, since she was the daughter, not of the divine Minerva, but of Pallas, the giantess. The name of Irene, recommended for the planet discovered on the 20th of May, 1851, will be hailed by all as an emblem of the peaceful reign of science. Gauss has urged the necessity of determining accurately the relative brightness of the planetoids, of which Vesta still remains the chief. This will not be an easy task. Clio, at least, seems to be variable in brightness. Mr. Ferguson, of the Washington Observatory, states that, on the 1st and *Astron. Theor. et Prat., II. 547. Astron. Journal, I. 139. † Compt. Rend., XXXII. 48, 95, 947. 2d of March, 1851, Clio appeared as a "star of the twelfth magnitude; on the 3d it was scarcely seen, though the comparison star was as bright as on the first nights. On the 4th, the planet surpassed its original brilliancy." 66 # The recent discoveries have impaired the little probability which still attached to the conjecture of Olbers, thrown out nearly fifty years ago (1802),† namely, that the planetoids are fragments of an exploded planet. In 1812 Lagrange read a paper before the French Bureau of Longitude on the Origin of Comets, in which he calculates that the force necessary to drive a planet into such an orbit as that of Pallas is twenty times that which impels a twenty-four pounder. In this calculation, Lagrange made no account of the mutual gravitation of the parts, or of the cohesive attraction which must be overcome by the force which produced the fracture and impelled the fragments in their various new orbits. Lagrange admitted that Olbers's hypothesis was not devoid of probability. But the language of Delambre in reference to Lagrange's paper is extraordinary. "This conjecture has been almost demonstrated by what remains to be told." § Still more remarkable are the words of Smyth: Although the strange coincidences attending this group may be accidental, in general phrase, yet their phenomena cannot but be considered as evidence tantamount to demonstration, of their having once composed a single planet, and having diverged by the explosive force of a tremendous cataclysm; and, in addition to their orbital vagaries, the bodies themselves are not round, as is said to be indicated by the instantaneous diminution of their light on presenting their angular faces.'|| Had such an accident as Olbers imagined ever occurred in the solar system, the splintered planets must all have had one common point of intersection in their orbits. At an early day, Gauss calculated the time required for the ordinary changes in the lines of nodes and the lines of apsides to efface all vestige of their common origin from the orbits of these planets as completely as it is now wanting, and he comes to this conclusion: “If we, therefore, adopt the hypothesis of Olbers, concerning the origin of the new planets, the occurrence must have taken place at an epoch immeasurably antecedent to the times to which our history reaches back.” Since the number of these bodies has increased from four to fifteen, it seems no longer within the power of mathematicians to calculate the time when all their orbits had a common line of intersection, and an equal radius vector at that place. As the aphelion distance of some of these orbits is less than the perihelion distance of others, no change in the lines of apsides could ever bring all these planets to the same point of space. The objections to Olbers's theory are strongly stated in the publication of Professor Loomis on the Recent Progress of Astronomy. * Astronomical Journal, I. 188. 1 Conn. de Tems, 1814. || Cycle, I. 160. † Monat. Corr., VI. 88. § Astronomie, II. 553. ¶ See B. A. Gould's paper in Silliman's Journal, VI. 1848. Also, Sill. Journ., VII. 447; Astr. Nachr., XXVI. 653, 659, and XXXIII. 17, 18. We shall close these remarks upon the planetoids with the following table, which contains their elements of motion. ELEMENTS OF THE ORBITS OF THE ASTEROIDS,* Arranged in the Order of their Mean Distance from the Sun. Of all the satellites, our moon is the one in which astronomers are most interested, and with which they are best acquainted. Delambre ‡ commemorates Galileo's graphic explanation of the moon's librations, by which she exposed to the gaze of the earth first her right ear and then her left; in the morning the hair around her forehead, and in the evening her chin. In * Astr. Nachr., No. 626, 636, 643, 641, 615, 630, 702, 773; Astr. Journ., I. 68, 91, 93, 127 ̧ 144, 152, 158, 163, 166, 168, 188; II. 4. †The sun's distance is the unit. ↑ Astronomie Moderne, I. 624. |