ROSENBERG, HANS OSWALD

(b. Berlin, Germany, 18 May 1879; d. Istanbul, Turkey, 26 July 1940)

astronomy, astrophysics.

The son of a merchant, Rosenberg attended the Wilhelms-Gymnasium in Berlin. In 1899 and 1900 he studied astronomy and other sciences at the Universities of Munich, Berlin, and Strasbourg. He completed his doctoral dissertation at Strasbourg in 1904. The subject, which he chose at the suggestion of Gustav Müller of Potsdam, was an investigation of the variation of the long-period variable star χ Cygni.

At Strasbourg in 1904 Rosenberg observed the occultation of α Tauri. He also developed a method for determining the paths of meteors and applied it to the bright meteor of 21 March 1904. He then turned his attention exclusively to photometry, fitting a recording wedge-photometer of his own design to the Strasbourg observatory’s six-inch refractor in order to measure the brightness of the comet 1903 IV. Using the same arrangement, Rosenberg determined the zero point of stepwise estimations of brightness measurements of the variable star Wx Cygni. This method was used by C. Wirtz in 1906 and 1907 to measure the brightness of Saturn. Rosenberg also developed a new design for the wedge photometer that lightened and simplified it.

To acquire more experience in the techniques of spectrophotometry, Rosenberg went in 1907 to Göttingen, where K. Schwarzschild placed the university observatory’s ultraviolet prism camera at his disposal. First Rosenberg made spectrographs of the comet 1907 IV. From 1907 to 1909 he observed the sun and seventy bright stars up to the third magnitude. In the course of this program he recorded 378 spectra and measured them with the Hartmann microphotometer. A short report on this work appeared in 1913, and the complete results were published the following year. From these data Rosenberg derived the color temperatures of many stars. In general his values were higher than those that J. Scheiner and J. G. Wilsing at Potsdam had obtained on the basis of visual observations. This discrepancy stimulated further study of the question.

At Göttingen, Rosenberg also investigated the relationship between brightness and spectral type among the Pleiades. With this study, which had been suggested by Schwarzschild, Rosenberg qualified as lecturer at the University of Tübingen in 1910. Rosenberg erected a private observatory on the Österberg, furnished with a 4.5-meter dome and a 130-mm. refractor fitted with a double camera. Among his first projects there was a spectrographic study of the nova Geminorum 2 of 1912.

From 1913 to 1921 (except during the war) Rosenberg concentrated on photoelectric photometry. In 1919, with P. Goetz, he made a photometric study of the lunar surface, using a potassium cell. In connection with this work he also developed a new type of polarization photometer. Other studies dealt with photographic star disks and with the brightness of the atmosphere in the neighborhood of brighter stars (Sirius, 1919); with the “influence of focusing on photographically effective wavelengths”; and with “the establishment of a normal sequence for the determination of effective wavelengths” (in collaboration with O. Bergstrand).

In 1921 Rosenberg began to study ways of increasing the strength of photocells by means of electron tubes. He also investigated previously unknown forms of photoelectric fatigue in alkali-metal cells. In 1925 Rosenberg designed an electromicrophotometer for making photometric measurements of the smallest focal star disks. With this instrument not only the photocell but also the electrometer could be used as a zero-point indicator. While working on this problem Rosenberg also determined the general reliability of the recording photometer (1925).

On 1 April 1926 Rosenberg accepted a position at the University of Kiel; as part of the agreement he was named director of its astronomical observatory. He had his instruments brought from Tübingen and supervised a complete refitting of the observatory that, in effect, adapted it for astrophysical research. In addition, he devoted considerable time to teaching. Once again Rosenberg concentrated primarily on photometric and spectrophotometric studies, and he organized two expeditions to measure solar eclipses, to Lapland in 1917 and to Thailand in 1929. Appointed dean of the Philosophy Faculty in 1930, he continued to produce scientific monographs.

Forced to leave Kiel for political reasons in 1934, Rosenberg accepted a visiting professorship at the University of Chicago. While working at the university’s Yerkes Observatory, he developed a double filter that made possible simultaneous photographs and cleanly separated focal images and extrafocal images. Rosenberg continued to make photographicphotometric observations of variable stars until 1937. In 1938 he went to Istanbul as university professor and director of the observatory. He was given responsibility for erecting a new observatory, but he succumbed to heat stroke in 1940 and was unable to complete the project. The year before his death he had been elected to the International Astronomical Union.

BIBLIOGRAPHY

I. Original Works. Rosenberg’s writings include Der veränderliche Stern χ Cygni (Halle, 1906); “Photographische Untersuchung der Intensitätsverteilung in Sternspektren,” in Nova acta Leopoldina, 101 no. 2 (1914); “Strahlungseigenschaften der Sonne,” in Handbuch der Physik, XIX (Berlin, 1928); “Lichtelektrische Photometrie,” in Handbuch der Astrophysik, II, pt. 1 (Berlin, 1929), 380–430, and VII (Berlin, 1936), 84–89; and Die Entwicklung des räumlichen Weltbildes der Astronomie, Kieler Universitätsreden, no. 11 (1930), 3–27.

II. Secondary Literature. See W. Gleissberg, “Hans Rosenberg,” in Istanbul üniversitesi fen fakültesi mecmuasi, 5 fasc. 1–2 (1940), 36–39, with portrait and bibliography, also in Istanbul üniversitesi Orman fakültesi yayinlari, 13 (1940); C. Schmidt-Schönbeck, “Hans Rosenberg,” in 300 Jahre Physik und Astronomic an der Kieler Universität (Kiel, 1965), 196–200, 260; and C. Schönbeck, “Physik and Astronomic,” in K. Jordan, ed., Geschichte der Mathernatik, der Naturwissenschaften und der Landwirtschaftswissenschaften (Neumünster, 1968), 59–93; and Handbuch der Experimentalphysik, XXVI, Astrophysik, B. Strömgren, ed. (Leipzig, 1937), 40; and J. G. Wilsing, “Über effektive Sterntemperaturen,” in Astronomische Nachrichten, 204 (1917), 153–159.

Diedrich Wattenberg