HAGEN, JOHANNES GEORG. - Jesuit, astronomer, b. at Bregenz (Austria) on 6 March 1847, d. at Rome on 6 Sept. 1930. A professor of mathematics in the United States of America, first at Prairie-du-Chien (Wisconsin), where he built 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, on the suggestion of the archbishop of Pisa, Pietro Maffi, later a cardinal, to direct the Vatican Observatory.
A tireless worker, a happy and rapid organizer, he contributed to the mathematical and astronomical sciences with a powerful series of articles and memoirs in numerous scientific periodicals (Astronomical Journal, Astrophysical Journal, Astronomische Nachrichten, Atti della Pontificia accademia delle scienze, etc.) and with works of lasting value. The following are remembered: 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). The capital work remains the Catalogo astrografico (10 vols., Rome 1921-28), in which are contained the rectangular coordinates of nearly 500,000 stars belonging to the zone of the sky assigned to the Vatican Observatory. The latter thus came to take fifth place among the observatories that had fulfilled in time their commitment to photograph the part of the sky entrusted to them. Fr. H. also worked on dark nebulae, on the colors of the stars, and on the fall of heavy bodies.
On the occasion of his 80th birthday, Pius XI wished to honor him with a visit, giving him a gold medal struck expressly for him (cf. Civ. Catt., Cronaca, 1927, I, pp. 555-56).