Christen Sørensen Longomontanus

Christen Sørensen Longomontanus (1562 to 1647) was a Danish astronomer whose Latinised name comes from the village of Lomborg in Jutland, where he was born into a labourer family. After a childhood of fieldwork and parish teaching he reached Copenhagen in 1588 with a reputation for learning, and from 1589 he worked for eight years as assistant to Tycho Brahe at the Uraniborg observatory, later completing the Tychonic lunar theory in Prague. He became professor at the University of Copenhagen in 1605 and held its chair of mathematics from 1607. His main work, the Astronomia Danica of 1622, developed the Tychonic geoheliocentric system into a complete treatise, keeping a daily rotation of the Earth. He also began the Round Tower in Copenhagen in 1632, and a lunar crater is named for him.