HAGEN, JOHANNES GEORG. — Jesuit, astronomer, born in Bregenz (Austria) on 6 March 1847, died in Rome on 6 September 1930. Professor of mathematics in the United States of America, first at Prairie-du-Chien (Wisconsin), where he erected a rudimentary observatory for the study of variable stars (1880–87), and then at Georgetown (Washington), as director of the Observatory (1887–1906), he was subsequently called by Pius X, in 1906, at the suggestion of the archbishop of Pisa, Pietro Maffi, later a cardinal, to direct the Vatican Observatory.
An indefatigable worker and a capable, rapid organizer, he contributed to the mathematical and astronomical sciences through a formidable series of articles and memoirs in numerous scientific periodicals (Astronomical Journal, Astrophysical Journal, Astronomische Nachrichten, Atti della Pontificia accademia delle scienze, etc.) and through works of lasting value. The following may be mentioned: Synopsis der höheren Mathematik (4 vols., Berlin 1891–1931); Index operum Leonardi Euleri (ibid. 1896); Atlas stellarum variabilium (7th series; I–VI, Berlin 1899–1908; VII, Rome 1927, followed by numerous additions); La rotation de la terre. Ses preuves mécaniques anciennes et nouvelles (Rome 1911); La rotation de la terre. Continuation des expériences (ibid. 1912); Die veränderlichen Sterne (2 vols., Freiburg im Breisgau 1913–24). His principal work remains the Catalogo astrografico (10 vols., Rome 1921–28), which contains the rectilinear coordinates of nearly 500,000 stars belonging to the region of the sky assigned to the Vatican Observatory. The latter thus came to occupy fifth place among the observatories that had completed in due time their task of photographing the portion of the sky entrusted to them. Fr. H. also worked on dark nebulae, the colors of stars, and the fall of heavy bodies.
On the occasion of his eightieth birthday, Pius XI wished to honor him with a visit, presenting him with a gold medal, expressly minted for him (cf. Civ. Catt., Cronaca, 1927, I, pp. 555–56).