Tycho Brahe was the Danish astronomer who built Uraniborg on the island of Hven in the 16th century.
King Frederick II granted Brahe the island of Hven, now called Ven, in 1576. There Brahe established Uraniborg and the underground observatory Stjerneborg. Before telescopes were used in astronomy, he made exceptionally precise observations with large naked-eye instruments.
Brahe’s measurements of planets, especially Mars, later enabled Johannes Kepler to formulate his laws of planetary motion. Brahe supported a geoheliocentric model in which the planets orbited the Sun while the Sun orbited Earth. The observatories no longer survive in their original form, but their sites are preserved as important landmarks in astronomical history.