– Niels Bohr Institute - University of Copenhagen

21 August 2009

The Round Tower. Copperplate, 1657

Købmagergade 52A

The Round Tower 

To the right of the entrance to the Round Tower there is a bust of Tycho Brahe (1546-1601) by S. Wagner (1932). Brahe was born in Skåne (Scania), then Danish, now part of Sweden. He studied law at the University of Copenhagen from 1559 to 1562 according to the wishes of his family, but eventually became an astronomer after years of study in Leipzig and Wittenberg, among other places. In 1576 the Danish King Frederick II gave him the island of Ven in the sound between Denmark and Scania, on which he practiced astronomy as well as alchemy and astrology.

Brahe left Denmark in 1597, when he lost favor with the Danish King Christian IV, and settled in Prague, where he was joined by Johannes Kepler (1571-1630) who became his assistant. Brahe died there in 1601.

The Round Tower is the oldest preserved observatory in Europe. It still functions as such; it served as the University of Copenhagen Observatory until 1861, and nowadays in the winter period anyone can observe the night sky through its fine astronomical telescope.

Statue of Tycho Brahe at the entrance to the Round
Tower. Courtesy of the Niels Bohr Archive.

The foundation stone of the Round Tower was laid in 1637, and the building was completed in 1642. The observatory was the first of a complex of three buildings built in the 17th century for use by scholars, the other two being the students' church (Trinitatis or Trinity Church, consecrated in 1656) and the university library (above the church). These buildings were commissioned by King Christian IV, who reigned from 1588 to 1648. There is a large and decorative riddle, designed by the King himself, on the outside of the Round Tower, which can be interpreted as follows: ‘‘Lead, O God, learning and justice into the heart of the crowned King Christian IV, 1642.''

Inside the tower a 209-meter-long spiral ramp leads up to the astronomers' study, directly underneath the observation platform, which is reached by a winding staircase. From here the visitor has a magnificent view of the old part of Copenhagen, including the University district, the Latin quarter. The first director of the observatory was Christian Longomontanus (1562-1647), one of Tycho Brahe's students.

Copenhagen has suffered many fires and bombardments over the centuries. The observatory and the university library burned in the fire of 1728, in which Tycho Brahe's celestial globe (which had been returned to Denmark in 1632) melted. Not one of Brahe's instruments is now to be found in Denmark.

At the end of the spiral ramp there is a planet plotter, installed in 1928, which shows the six inner planets' orbits around the Sun. The original planet plotter was constructed in 1697 by Ole Rømer, who was a convinced Copernican, but out of veneration for Tycho Brahe, Rømer adapted the first planet plotter according to Brahe's system with the Earth at the center, the Sun moving around the Earth, and the rest of the planets moving around the Sun.

The library hall above the church was used as the university library in the years 1657-1861. It is now used as an exhibition hall. The entrance is halfway up the spiral ramp.

The Round Tower: http://www.rundetaarn.dk/

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