Uranienborg was a Danish astronomical observatory operated by Tycho Brahe. It was the first custom-built observatory and the last to be built without a telescope as its primary instrument.

Uranienborg (or Uraniborg) was built c. 1576 – c. 1580 on Hven, an island in the Øresund by the support of Frederick II, King of Denmark and Norway. The main building of Uraniborg was square, about 15 meters on a side, and built mostly of red brick. Two semi-circular towers, one each on the north and south sides of the main building, gave the building a somewhat rectangular shape overall. The observatory had a large mural quadrant affixed to a north-south wall, used to measure the altitude of stars as they passed the meridian. Uraniborg was an extremely expensive project. It is estimated that it cost about 1% of the entire state budget during construction. Shortly after construction it became clear that the tower-mounted instruments were too easily moved by wind, and Tycho set about constructing a more suitable observation site. The result was Stjerneborg ("castle of the stars"), a smaller site built entirely at ground level and dedicated purely to observations (there was no "house"). Upon losing financial support from the new king, Christian IV of Denmark, Tycho abandoned Hven in 1597 and both Uraniborg and Stjerneborg were destroyed shortly after Tycho's death.

A bronze medal was issued in 1976 to celebrate the 4th centenary of the foundation of Uranienborg. On its obverse the reconstruction of the building, standing on the half-cut globe dominates the scene. Above the building scattered stars are placed. The letter T and B refers to Tycho Brahe. Below: "1576 · URANIENBORG · 1976".

Uraniborg 1 reverseUraniborg 1 obverse

The reverse shows Brahe as he stands in a window holding an astronomical instrument. The legend is: "TYCHO BRAHE · URANIENBORG". Following the legend five stars forming the Cassiopeia constellation is depicted, perhaps referring to the supernova of Cassiopeia in 1572, that was discovered by Tycho Brahe.