Rosenberger, Otto August
ROSENBERGER, OTTO AUGUST
(b. Tukums, Latvia, 10 August 1800; d. Halle, Germany, 23 January 1890)
Rosenberger was the son of a physician who moved with his family to Königsberg in 1811. He attended the Königsberg Gymnasium, then entered the university, where he studied mathematics and astronomy and formed the tie with Bessel that determined the direction of his professional life. While still a student he worked with Bessel in making observations and computations, and from 1821 on was regularly mentioned in the Astronomische Beobachtungen auf der K. Universitätssternwarte zu Königsberg, which Bessel edited. On 18 June 1821 Bessel wrote to H. C. Schumacher that the observations of the chief stars that he had made with the Cary circle had been “very accurately computed” and reduced to the year 1815 by his students Rosenberger and H. F. Scherk. Rosenberger and Scherk had also computed the elements of the Pons comet of 1818, and Rosenberger determined the parabolic elements of it; his results were published in the Berliner astronomisches Jahrbuch for 1824.
Bessel further entrusted Rosenberger with computing the elements and ephemerides of the comet of 1821; these findings appeared in the first issue of the Astronomische Nachrichten in the following year. “Rosenberger,” Bessel wrote of this work, “has been able to represent all the observations—the European ones made before the perihelion as well as the American ones made after it—in the form of a parabola; and the errors do not exceed the uncertainties of the observations.” Indeed, Bessel thought so highly of Rosenberger’s promise that when his assistant Argelander left the Königsberg observatory in 1823, Bessel named Rosenberger to replace him.
Bessel first assigned Rosenberger to compute a number of occultations of the Pleiades so as to obtain more accurate values for the distances between the observatories at which the observations had been made. Rosenberger also participated in Bessel’s zone observations (an error in this work became known only in 1861, when Eduard Schönfeld demonstrated that in an observation of zone 285, performed on 23 April 1825, Rosenberger had confused the asteroid Pallas with a fixed star). In 1824 Rosenberger computed a new catalogue, which appeared in the Astronomische Beobachtungen as “Verzeichnis der geraden Aufsteigungen der 36 Fundamentalsterne für 1825.” This catalogue was based upon the observations that he had made with the Königsberg meridian circle between 1821 and 1824; he also took part in the observation of the comet of the latter year and of the “moon stars.”
On 23 May 1826 Rosenberger was named, on Bessel’s recommendation, to succeed J. F. Pfaff at the University of Halle with the positions of extraordinary professor of mathematics and director of the observatory. Having completed the requirements for the doctorate, which was awarded him by the University of Königsberg on 16 July of the same year, Rosenberger went to Halle to take up his new duties the following October. He found that the observatory there, which had been erected in 1790 for exclusively pedagogical purposes, was sadly underequipped, and offered him no opportunity to conduct systematic observations. He therefore turned to theoretical studies, and in 1827 published an examination of the results reported by an expedition sent to Lapland by the Paris Académie des Sciences in 1736–1737. The purpose of this venture, which was supervised by Maupertuis, was to measure the length of a degree of longitude; the resulting measurements had provoked considerable criticism, but Rosenberger, after carefully weighing the merits of the undertaking, concluded that the work was valid.
In 1830 a small meridian circle, a Fraunhofer telescope with a focal length of seventy-two inches, and two astronomical clocks were installed in the Halle observatory at Rosenberger’s request. He was thus able to carry out occasional astronomical observations as part of his teaching. On 5 July 1831 he was promoted full professor.
In 1834, shortly before the expected reappearance of Halley’s comet, Rosenberger, working part of the time with Olbers, made new computations of the comet’s orbital elements and ephemerides. His results were in close accord with the later actual observations. In a series of separate publications, he investigated the elements of the comet during its appearances in 1682 and 1759, and gave an account of its perturbations during the intervening period. These were his last publications; he devoted the rest of his career to his teaching and administrative duties, and continued to lecture enthusiastically even after his retirement in 1879.
A bibliography of Rosenberger’s writings is in General-Register der Astronomischen Nachrichten, Bände 1 bis 40 (Kiel, 1936), 94. Thirty-seven letters from Rosenberger to Bessel (1821–1835) and seventeen letters from Rosenberg to H. C. Schumacher (1827–1835) are in the archives of the Akademie der Wissenschaften der DDR, Berlin.
Biographical material is in the obituary by A. Wangerin, “Otto August Rosenberger,” in Astronomische Nachrichten, 123 (1890), 415–416.