(b. Hildburghausen, Germany, 22 December 1828; d. Bonn, Germany, 1 May 1891)
Schönfeld was educated at the Gymnasium in Hildburghausen. He then attended the Technische Hochschule at Hannover, from which he was expelled in 1849 because of his involvement in the political unrest of 1848. Schönfeld continued his technical studies at Kassel but found them unsatisfactory and began to study chemistry and astronomy at Marburg University in the autumn of 1849. In 1852 he went to Bonn University, where he was introduced to Argelander and became his assistant in 1853; the following year Schönfeld received his doctorate. In 1859 he was appointed director of the observatory at Mannheim. When Argelander died in 1875, Schönfeld succeeded him as director of the Bonn observatory and as professor of astronomy at the university. An active member of the Astronomische Gesellschaft, he served as secretary from 1875 until his death.
Schönfeld’s name is very closely connected with the Bonner Durchmusterung, a catalog of all stars down to the ninth magnitude begun by Argelander. Schönfeld was one of his most enthusiastic collaborators and made a great many of the necessary observations using a telescope having an aperture of not more than about three inches. Schönfeld also performed most of the preparatory work for the publication of the results. After Argelander’s death, he started work to expand the Durchmusterung to include more southern declinations; within ten years he completed the Schönfeld-Durchmusterung, which extended Argelander’s Durchmusterung from declination–2° down to—23°. All observations for this work were made by Schönfeld himself. The great importance of these Durchmusterungen is best shown by the fact that in 1967, almost a century later, they were completely reprinted.
Schönfeld also observed nebulae, variable stars, and comets. He published the results of his observations of nebulae at Mannheim in two catalogs that appeared in 1862 and 1875.
Schönfeld collaborated with Argelander and A. Krüger on “Bonner Sternverzeichnis,” Astronomische Beobachtungen auf der Sternwarte zu Bonn, 3 (1859); 4 (1861); and 5 (1862). He was sole author of “Bonner Sternverzeichnis,” ibid., 8 (1886).
See also E. von der Pahlen, Lehrbuch der Stellarstatistik (Leipzig, 1937), 182, 341.