LONGOMONTANUS (or LONGBERG), CHRISTIAN SEVERIN Danish astronomer, was born at Long berg in Jutland, Denmark, on Oct. 4, 1562. The appellation Longomontanus was a Latinized form of the name of his birth place. In he ran away to Viborg, where he attended the grammar-school, defraying his expenses by manual labour, and went to Copenhagen in 1588 with a high reputation for learning and ability. Engaged by Tycho Brahe in 1589 as his assistant in his great astronomical observatory of Uraniborg, he rendered him invaluable services there during eight years. He quitted the island of Hveen with his master, but obtained his discharge at Copenhagen on June 1, 1597, for the purpose of studying at some German universities. He rejoined Tycho at Prague in January 160o, and having completed the Tychonic lunar theory, turned homeward again in August. He visited Frauenburg, where Coper nicus had made his observations, took a master's degree at Rostock, and at Copenhagen found a patron in Christian Friis, chancellor of Denmark, who gave him employment in his house hold. Appointed in 1603 rector of the school of Viborg, he was elected two years later to a professorship in the university of Copenhagen, and his promotion to the chair of mathematics ensued in 1607. This post he held till his death, on Oct. 8, He inaugurated, at Copenhagen in 1632, the erection of a stately astronomical tower, but did not live to witness its com pletion. Christian IV. of Denmark, to whom he dedicated his
Astronomia Danica, an exposition of the Tychonic system of the world, conferred upon him the canonry of Lunden in Schleswig.
The following is a list of his more important works in mathematics and astronomy: Systematis Mathematici, etc. (I6ii) ; Cyclometria e Lunulis reciproce demonstrata, etc. (1612) ; Disputatio de Eclipsibus (1616) ; Astronomia Danica, etc. (1622) ; Disputationes quatuor Astrologicae (1622) ; Pentas Problematum Philosophiae (1623) ; De Chronolabio Historico, sea de Tempore Disputationes tres (1627) ; Geometriae quaesita XIII. de Cyclometria rationali et vera (1631) ; Inventio Quadraturae Circuli (1634) ; Disputatio de Matheseos Indole (1636) ; Coronis Problematica ex Mysteriis trio n Numerorum (1637) Problemata duo Geometrici (1638) ; Problema contra Paulum Guldinum de Circuli Mensura (1638) ; Introductio in Theatrum Astronomicum (1639) Rotundi in Plano, etc. (1644) ; Admiranda Operatio trium Numerorum 6, 7, 8, etc. (1645) ; Caput tertium Libri primi de absoluta Mensura Rotundi plani, etc. (1646).
See J. B. J. Delambre, Hist. de l'astr. moderne, i. 262 ; J. S. Bailly, Hist. de l'astr. moderne, ii. 141; J. L. E. Dreyer, Tycho Brahe, pp. 126, 259, 288, 299; F. Hoeffer, Hist. de l'astronomie, p. 391 ; J. Madler, Geschichte der Himmelskunde, i. 195 ; J. F. Weidler, Hist. Astronomiae, P.