Wilsing, Johannes

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(b. Berlin, Germany, 8 September 1856; d. Potsdam, Germany, 23 December 1943)


Wilsing received his doctorate from the University of Berlin in 1880 and the following year became assistant at the Potsdam Astrophysical Observatory. In 1893 he received the post of observer and, in 1898, chief observer. He retired in 1921.

Wilsing conducted many observations concerning problems in astrophysics, a relatively new branch of astronomy at the time. He observed the velocity of rotation of the sun and offered a hydrodynamic explanation of its variation with latitude. Several of his studies deal with the influence on astrophysical measurements of systematic errors, such as atmospheric dispersion or optical and mechanical deficiencies of telescopes. He also observed novae, nebulae, and double stars.

Several of Wilsing’s publications deal with methods, such as the derivation of the surface temperature of a star from photometric measurements of its spectrum. In calculating the diameters of stars, he used the laws of radiation and the measured values of the surface temperature, from which the radiating area can be computed. Although this method was not new in principle. Wilsing was the first to apply it systematically. His results were confirmed some years later, when the first interferometric measurements of stellar diameters were made.


I. Original Works. Wilsing’s writings include Determination of the Mean Density of the Earth by Means of a Penchdunr Principle, J. H. Gore, trans. (Washington, 1890): “Uber die Helligkeitsverteilung im Sonnenspektrum nach Messungen an Spektrogrammen,” which is Publikctione, des Astrophvsikalischen Observatorimn. zu Potsdam, 22 , no. 66 (1913): and “Messungen der Farben, der Helligkeiten and der Durchmesser der Sterne mit Anwendung der Planckschen Strahlungsgleichung,” ibid., 24 , no. 76 (1920).

See also the Royal Society Catalogue of Scientific Papers, XIX, 644–645, which lists 38 memoirs published to 1900: and Poggendorff, IV, 1645–1646: V, 1376–1377: VI, 2896: and Vila, 1015.

II. Secondary Literature. See E. von der Pahlen, Lehrbuch der Stellarstatistik (Leipzig, 1937); and M. Waldmeier, Ergebnisse und Probleme der Sonnenforschung (Leipzig, 1941).

F. Schmeidler