Longomontanus

Longomontanus, born Christen Sørensen Longomontanus, was a Danish astronomer and mathematician. He was a prominent figure in the scientific community of the late 16th and early 17th centuries. Longomontanus is perhaps best known for his significant contributions to the study of the Sun's motion and his work on trigonometry.

He studied under Tycho Brahe at the island observatory of Uraniborg. After Brahe's death, Longomontanus inherited many of his astronomical observations. He meticulously analyzed this data, which formed the basis for many of his later discoveries. His most famous work, Astronomia Danica, published in 1622, presented a geocentric model of the solar system, which, while ultimately superseded by heliocentric models, was highly influential in its time.

Longomontanus also made notable advancements in trigonometry. His book, De triangulis planis et sphaericis tractatus brevis et perspicuus (A Brief and Clear Treatise on Plane and Spherical Triangles), published in 1611, was a comprehensive text that simplified and systematized the field. He introduced new methods and theorems, making trigonometry more accessible for other scholars. His work played a crucial role in the development of practical applications of mathematics, particularly in navigation and surveying. He spent much of his later career as a professor at the University of Copenhagen.