LONGOMONTANUS (or LONGBERG), CHRISTIAN SEVERIN (1562-1647), Danish astronomer, was born at the village of Longberg in Jutland, Denmark, on the 4th of October 1562. The appellation Longomontanus was a Latinized form of the name of his birthplace. His father, a poor labourer called Soren, or Severin, died when he was eight years old. An uncle thereupon took charge of him, and procured him instruction at Lemvig; but after three years sent him back to his mother, who needed his help in field-work. She agreed, however, to permit him to study during the winter months with the clergyman of the parish; and this arrangement subsisted until 1577, when the illwill of some of his relatives and his own desire for knowledge impelled him to run away to Viborg. There he attended the grammar-school, defraying his expenses by manual labour, and carried with him to Copenhagen in 1588 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 the 1st of June 1597, for the purpose of studying at some German universities. He rejoined Tycho at Prague in January 1600, and having completed the Tychonic lunar theory, turned homeward again in August. He visited Frauenburg, where Copernicus 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 household. 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 the 8th of October 1647.
Longomontanus, although an excellent astronomer, was not an advanced thinker. He adhered to Tycho's erroneous views about refraction, held comets to be messengers of evil and imagined that he had squared the circle. He found that the circle whose diameter is 43 has for its circumference the square root of 18252 which gives 3-14185 . . . for the value of ir. John Pell and others vainly endeavoured to convince him of his error. He inaugurated, at Copenhagen in 1632, the erection of astately astronomical tower, but did not live to witness its completion. 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. (1611); 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, sen de Tempore Disputationes tres (1627) ; Geometriae quaesita XIII. de Cyclometria rationali et vera (1631); Inventio Quadraturae Circuit (1634); Disputatio de Matheseos Indole (1636); Coronis Problematica ex Mysteriis trium Numerorum (1637); Problemata duo Goemetrica (1638); Problema contra Paulum Guldinum de Circuli Mensura (1638) ; Introductio in Theatrum Astronomicum (1639); Rotundi in Piano, etc. (1644); Admiranda Operatic trium Numerorum 6, 7, 8, etc. (1645) ; Caput tertium Libri primi de absolute, Mensura Rotundi plant, etc. (1646).
See E. P. F. Vindingius, Regia Academia Havinensis, p. 212 (1665) ; R. Nyerup and Kraft, Almindeligt Litteraturlexikon, p. 350 (1820); Ch. G. Jocher, Allgemeines Gelehrten-lexikon, ii. 2518, iii. 2111 ; Jens Worm, Forsog til et Lexikon over danske, norske og islandske laerde Maend,p.6lf, 1771, etc. ; P. Bayle, Hist, and Crit. Dictionary, iii. 861 (2nd ed. 1736); J. B. J. Delambrei Hist, de I'astr. moderne, i. 262; J. S. Bailly, Hist, de I'astr. moderne, ii. 141; J. L. E. Dreyer, Tycho Brahe, pp. 126, 259, 288, 299; F. Hoeffer, Hist, de I' astronomie , P- 39 1 ! J- Madler, Geschichte der Himmelskunde, i. 195; J. F. Weidler, Hist. Astronomiae, p. 451.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)