Schiaparelli, Giovanni Virginio
SCHIAPARELLI, GIOVANNI VIRGINIO
(b. Savigliano, Cuneo province, Italy, 14 March 1835; d. Milan, Italy, 4 July 1910)
After receiving his degree in civil engineering at Turin in 1854, Schiaparelli taught mathematics and studied modern languages and astronomy at the University of Turin. As a result of his increasing interest in astronomy, in 1857 he was sent by the Piedmont government to continue advanced studies at the observatories of Berlin and Pulkova. On his return to Italy in 1860. Schiaparelli was appointed astronomer at the Brera Observatory in Milan; and in 1862, when his work had already brought him a certain renown, he succeeded Francesco Carlini as director. He retired voluntarily in 1900 and spent the rest of his life in Milan. In 1889 Schiaparelli became senator of the kingdom of Italy, he also was a member of the Lincei and of many other Italian and foreign academies. He received gold medals from the governments of Italy, England, and Germany, and twice won the Lalande Prize of the Institut de France.
At the beginning of his observations at Brera, Schiaparelli, using primitive instruments, discovered the asteroid Hesperia. In 1860 he became interested in comets and undertook a theoretical study on the initial direction of their tails in which he demonstrated the existence of a repulsive force that tends to pull parts of the tail away from the part opposite the sun. This force, combined with gravity, generates in the tail a parabola, similar to that described by terrestrial projectiles.
The appearance of the bright comet of 1862 stimulated Schiaparelli’s interest in these celestial objects; and while observing it, he reflected on the forces that determine the features of comets in general. His accurate study of the shape and position of the tails of comets led him to new theories on the repulsive action exerted by the sun and to classify the tails according to this action.
Schiaparelli assiduously continued his observations of physical position and calculations of the orbits of comets while developing the idea that comets give rise to meteors. It was discovered that Biela’s comet, when it appeared in 1845, had split in two; and on its next appearance, in August 1852, Secchi found its larger fragment. The smaller fragment was discovered about a month later at a far greater distance from the first than had previously been calculated. It became clear that the comet was disintegrating as it approached the sun. In April 1862, still using the modest instruments available at Brera. Schiaparelli observed the large comet of that year and saw that the nucleus—the luminous head of the comet followed by a long tail—was emitting a luminous jet that rapidly increased in size and assumed the shape of a clearly outlined pear. Its mass was much greater than the nucleus proper, the form was that of a small cloud in which, over a clear background, more luminous points flared at intervals, like small stars visible in the field of a telescope.
The hypothesis had been advanced that meteor showers, observed over the centuries as originating from a well-defined point in the sky, could be related to the disintegration of comets. Schiaparelli’s hypothesis was based chiefly on his observations of the meteor swarms of August 1866. He stated the hypothesis more definitely in five letters to Secchi “concerning the course and probable origin of the meteoric stars,” Secchi published the letters in Bullettino meteorologico dell’Osservatorio del Collegio romano in 1866. To confirm his hypothesis Schiaparelli had to prove that if meteors are subject to the attraction of the sun, they must move in elliptical or parabolic ororbits around it and that these orbits must be identical with or similar to those of the comets that cause meteor swarms. The latter become visible when the earth, in its course around the sun, meets either of the swarms that extend along that in the planetary spaces the meteors must form a multitude of continuous currents that, on meeting the earth in its orbit, become visible in the form of luminous showers falling from a determined direction of the celestial sphere. Secchi accurately observed these directions (the “radiants”) and proved that the orbit of the periodic stars of August is practically identical to that of the large comet of 1862.
Schiaparelli published a complete elaboration of his theory as Entwurf einer astronomischen Theorie der Sternschnuppen (1871). Following the extraordinary meteor shower of 27 November 1872, he explained the phenomena and the theory behind them in three letters. In the third letter he stated:
The meteor showers are the product of the dissolution of the comets and consist of very minute particles that they ... have abandoned along their orbit because of the disintegrating force that the sun and the planets exert on the very fine matter of which they are composed.
Schiaparelli’s hypothesis on the origin of meteors, elaborated in depth and with elegance, has been fully confirmed in the several cases listed: these include the relation he discovered between the Perseids of 10 August and the great comet of 1862; C. H. F. Peters’ observations concerning the November Leonids in relation to the comet of 1866; and Galle’s and Weiss’s studies of the first comet of 1861 and the meteor shower of 20 April. A fourth case deals with Biela’s comet, the relations of which to certain previously observed meteors had been noted as early as 1867 by d’Arrest and Weiss and were confirmed by the meteor shower of 27 November 1872. The meteor showers of 1933 and 1946 related to the Giacobini-Zinner comet; the swarm of the Taurids, to Encke’s comet. Thus, Schiaparelli’s theory was confirmed.
In 1877, using a Merz refractor far superior to the antiquated instruments he had previously used, Schiaparelli turned his attention to the study of Mars. This exceptional instrument, with an objective aperture of twenty-two centimeters, revealed “a large quantity of minute objects, which in the earlier oppositions had been overlooked by the gigantic telescopes in which foreign countries justly take pride”. During the great opposition of Mars in 1877 Schiaparelli observed the planet thoroughly, detecting even the smallest surface features. He began to determine the orientation of Mars in the sky, publishing a first memoir in Astronomische Nachrichten; “Sur I’axe de rotation et sur la tâche polaire australe de Mars”. It was followed by Osservazioni astronomiche e fisiche sull’asse di rotazione e sulla topografia del pianeta Marte durante I’opposizione del 1877.
In drawing a complete picture of the areographic positions of the fundamental points for the construction of an accurate map, Schiaparelli stated that the interpretation of the phenomena observed on Mars was still largely hypothetical, varying among observers even when they saw the same details. He was the first to classify the features as “seas” and “continents”; the term “canal” had been used by Secchi in his observations of 1859. Schiaparelli’s was an original nomenclature, and he observed that “the names I adopted will in no way harm the cold and rigorous observations of facts”. Although he understood that the features he observed on Mars were stable, like their terrestrial counterparts, he was cautious in drawing conclusions on the nature of the surface and atmosphere until he could establish that the seas, continents, and canals were identifiable with analogous terrestrial formations.
During the opposition of 1879–1880 Schiaparelli continued his observations, from which he prepared a catalog of the positions of all visible topographical features. In it he sought to provide a less geometric interpretation than that of his first map of 1877–1878. Schiaparelli noted that because Mars was moving away from the earth, its diameter gradually decreased during subsequent oppositions. In 1879 he had observed that certain canals seemed to be splitting into two parts. In the 1881–1882 opposition he noted the increasing clarity of the geminations of canals, which he thought would greatly change current opinions on the physical constitution of the planet. His areographic map of this opposition apparently is a more geometric representation, perhaps in order to stress the gemination of the canals, which also appeared in the 1883–1884 oppositions. In the latter nearly all of them were split.
In his observations of the 1886 opposition, Schiaparelli used a new refractor with an aperture of fifty centimeters, among the largest at that time. The disk of the planet then measured only ten seconds in diameter and Schiaparelli, continuing to make increasingly geometric drawings, marked only one large gemination; the Nilus-Hydrae Fons. In the 1888 opposition, which occurred under good atmospheric conditions, he found it impossible to represent adequately all the detailed features and their colors. Observing the geminations that had been absent from the preceding opposition, Schiaparelli thought that their reappearance constituted a strictly periodic phenomenon related to the solar year of Mars, and that it was necessary to follow it closely in successive, and more favorable, oppositions. He noted that the split canals appeared and remained visible for a few days or weeks before again becoming simple canals or disappearing entirely.
Schiaparelli’s observations of Mars ended with the 1890 opposition. This cycle included seven oppositions that present all conceivable varieties of inclinations of the axis, of the apparent diameter, and of geocentric declination, and it occurred at points along the zodiac almost equidistant from each other. Schiaparelli recalled that three astronomers of the Lick observatory, using the refractor with a ninety-two- centimeter aperture, insisted they saw the same details differently through the same telescope and, one might say, at the same instant. Other observers, using less powerful instruments, saw a thick web of lines (the canals proper) so clearly that they could be recognized with good telescopes having an aperture of only ten centimeters. The last areographic map, which Schiaparelli drew at the conclusion of his observations, is the most geometric of all and depicts most of the canals as split. E. Antoniadi, another well-known observer of Mars, using a telescope with an eighty-three-centimeter aperture at the Meudon (Paris) observatory, noted in 1930 that Schiaparelli, with instruments of equal power, had surpassed everyone with his numerous observations.
Schiaparelli also observed Saturn and, for eight years, the few dark spots, visible on Mercury in the form of shadowy bands, difficult to recognize in full daylight. He concluded that Mercury revolves about the sun in the same manner that the moon does around the earth and Iapetus around Saturn—with the same side always truned to the sun. He also tried to solve the problem of the rotation of Venus on its axis. In outlining the history of the subject, which also concerned Jean-’Dominique Cassini, he recalled the observations made at Rome in 1726 by Francesco Bianchini. On the basis of the diffused and indefinite shadows visible on the surface, Bianchini had concluded that it completed one rotation on its axis in about twenty-four days and eight hours. Schiaparelli observed Venus in 1877 and 1878, noting luminous oval spots that were quite visible but transitory, perhaps resulting from variations in the planet’s atmosphere. He concluded that the rotation of Venus was “very slow ... , much slower than Bianchini had supposed”, From observations of well-defined spots, he obtained as a very probable result that the rotation occurs in 224.7 days, a period exactly equal to that of the sidereal revolution of the planet around an axis almost coincident with the perpendicular to the plane of the orbit.
Schiaparelli also made numerous observations of double stars. For many of the more interesting binaries, the measurements were continued for several years, in order to deduce the orbital elements of the systems.
Schiaparelli’s work in the history of astronomy was noteworthy. The orientalist C.A. Nallino was sent by the Brera Observatory to the Escorial to copy and translate into Latin the only existing Arab text of al-Battänï’s Opus astronomicum. Schiaparelli collaborated with Nallino to complete the translation, which was published by the Brera Observatory between 1899 and 1907. He also contributed many explanatory notes to several chapters. He noted that much more was known about Arab astronomy as a result of the translation of this vast work, which is not limited to the works of al-Battünï. A comparison between the Opus astronomicum and Ptolemy’s Almagest, with which there are many points of similarity is of special value to an understanding of the development of astronomy in the Arab world.
Schiaparelli had intended to compile a major work on the history of ancient astronomy. In preparation for it he read the original texts of the Hebrews, Assyrians, Greeks, and Romans. During his lifetime he published several mongraphs on the subject. These and many similar works that Schiaparelli was not able to complete were published by his pupil Luigi Gabba in 1925–1927.
The first volume deals with the astronomy of Babylonia, of the Old Testament lands, and of Greece. In the second volume he treats later Greek astronomy: the homocentric spheres of Eudoxus of Cnidus, Callippus, and Aristotle. Schaiparelli next considers the origin of the Greek heliocentric planetary system with Aristarchus of Samos, who, as Schiaparelli demonstrates, must have developed the system through the hypothesis proposed centuries later by Tycho Brahe. According to Schiaparelli’s research, the Tychonic system was known to the Greeks at the time of Heraclides Ponticus (fourth century B.C.). The second volume ends with minor writings on “parapegmata”, the astrometeorological calendars of the ancients. The third volume contains writings designed to integrate the history of ancient astronomy: his studies on the calendar of the ancient Egyptians; on the observations and ephemerides of the Babylonians; on the phenomena of Venus, according to the discoveries made in the ruins of Nineveh; on the discovery of the precession of the equinoxes; and on the astronomy of Hipparchus. These three volumes, even though they may not contain all that Schiaparelli had wanted to include in the project, nevertheless provide data and information of inestimable value on the history of ancient astronomy.
I. Original Works. Schiaparelli’s writings have been brought together in Le opere di G.V.Schiaparelli, 11 vols. (Milan, 1929–1943); and Scritti sulla storia della astronomia antica, Luigi Gabba, ed., 3 vols. (Bologna, 1925–1927).
II. Secondary Literature. See G. Abetti, Storia della astronomia (Florence, 1963), 224–228; and the obituary by E. Millosevich, in Memorie della Societadegli spettroscopisti italiani, 39 (1910), 138–140, with photograph.