Tycho Brahe and Uraniborg (1576): Astronomy Before the Telescope

Uraniborg, the observatory that the Danish nobleman Tycho Brahe built on the island of Hven from 1576, was the most advanced astronomical research centre in Europe before the telescope. Over some twenty years Tycho and his assistants measured the positions of stars and planets with unprecedented accuracy. Those records, inherited by Johannes Kepler, became the foundation of modern planetary astronomy.

Background: a nobleman astronomer

Tycho Brahe was born on 14 December 1546 at Knutstorp in Scania, then part of Denmark and now in southern Sweden, into one of the kingdom’s leading noble families. He studied at Copenhagen, Leipzig, Wittenberg, Rostock and Basel. A partial solar eclipse in 1560 is said to have drawn him to astronomy, and in 1563 he noticed that the published tables, both Ptolemaic and Copernican, predicted a conjunction of Jupiter and Saturn wrongly by days.

In December 1566, at Rostock, he lost part of his nose in a duel with a fellow Danish nobleman, Manderup Parsberg, and wore a metal prosthesis afterwards. On 11 November 1572 he noticed a new, brilliant star in the constellation Cassiopeia. By careful measurement he showed that it had no detectable parallax and therefore lay far beyond the Moon. His book De nova stella (1573) challenged the Aristotelian belief that the heavens were perfect and unchanging. The object is now known as supernova SN 1572.

Building Uraniborg

Tycho’s fame led King Frederick II of Denmark to offer him, in 1576, the island of Hven in the Øresund strait between Denmark and Scania, with its revenues, to keep him from settling abroad. The foundation stone of Uraniborg, named after Urania, the Muse of astronomy, was laid on 8 August 1576.

The main building, completed around 1580, was a Renaissance palace with domes, balconies and observing platforms, set in a square garden. It housed living quarters, a library, an alchemical laboratory in the basement and rooms for students and assistants. Tycho later added a paper mill and a printing press to publish his work.

Uraniborg was also a community. Over the years dozens of assistants, students and craftsmen lived and worked there; the historian John Robert Christianson identified more than a hundred people associated with Tycho’s household and research. Assistants took turns at the instruments through the night, recording observations in logbooks that were later copied and checked. Visitors included scholars and royalty: King James VI of Scotland, later James I of England, came to Hven in March 1590 while travelling to collect his Danish bride, Anne of Denmark.

The cost was enormous. Contemporaries and historians have estimated that Tycho’s establishment on Hven consumed a significant share of the Danish crown’s income at its height, often put at around 1 per cent or more, which made it one of the most expensive scientific projects of the age.

Because wind shook instruments on Uraniborg’s high platforms, from about 1584 Tycho built a second observatory nearby, Stjerneborg (“Castle of the Stars”), with instruments sunk partly below ground level for stability.

How Tycho observed

Tycho worked without a telescope, which was not invented until about 1608. His precision came from large, solidly built instruments, careful design of sights and scales, and repeated observation. His great mural quadrant, a brass arc about two metres in radius fixed to a wall running north–south, measured the altitude of stars as they crossed the meridian. Armillary spheres and sextants measured other angles.

He also checked his instruments against each other, estimated their errors and observed objects at many points along their paths rather than only at key moments. His best measurements were accurate to within about one to two minutes of arc, roughly a thirtieth of the Moon’s apparent width, several times better than earlier astronomers. His star catalogue, completed in the 1590s, eventually listed about 1,000 stars. He also corrected for atmospheric refraction, which makes objects near the horizon appear higher than they are, and he described his instruments in detail in Astronomiae instauratae mechanica (1598).

The comet of 1577 and the Tychonic system

Observations of the great comet of 1577 showed that it, too, lay well beyond the Moon and moved through regions supposedly filled with solid crystalline spheres. Tycho concluded that such spheres could not exist.

He admired Copernicus’s mathematics but could not accept a moving Earth, partly for physical and religious reasons and partly because he could detect no stellar parallax. In 1588 he published his own model: the Earth fixed at the centre, the Moon and Sun circling it, and the other planets circling the Sun. Geometrically this matched the Copernican predictions, and the Tychonic system became widely popular in the seventeenth century, especially among Jesuit astronomers.

Key people

• Tycho Brahe (1546–1601): Danish nobleman and astronomer, lord of Hven.
• Frederick II of Denmark (1534–1588): king who granted Hven and funded Uraniborg.
• Christian IV of Denmark (1577–1648): Frederick’s son, under whom royal support ended.
• Johannes Kepler (1571–1630): Tycho’s assistant in Prague and heir to his observations.
• Rudolf II (1552–1612): Holy Roman Emperor who employed Tycho as imperial mathematician.

Leaving Hven and the Kepler connection

After Frederick II died in 1588, Tycho’s position weakened. He clashed with the island’s tenants and with the young king Christian IV, and his revenues were cut. In 1597 he left Hven, taking portable instruments and his records. In 1599 he settled in Bohemia as imperial mathematician to Emperor Rudolf II.

In 1600 the young German mathematician Johannes Kepler joined him near Prague. Tycho assigned him the difficult orbit of Mars. Tycho died in Prague on 24 October 1601 after a sudden illness. Kepler then used the observations to formulate his laws of planetary motion, showing that planets move in ellipses, and in 1627 completed the Rudolphine Tables, named after the emperor.

Uraniborg fell into ruin and was largely demolished within a few decades. Hven passed to Sweden with Scania under the Treaty of Roskilde in 1658. Today the foundations, a reconstructed Renaissance garden, the restored Stjerneborg and a museum mark the site.

Myths and facts

• Myth: Tycho died because he was too polite to leave a banquet to relieve himself. Fact: Kepler’s account links his illness to a banquet, but the cause of death is uncertain; modern analysis points to a urinary or kidney condition rather than a burst bladder.
• Myth: Kepler or someone else poisoned him with mercury. Fact: tests on remains exhumed in 2010 found no mercury at lethal levels.
• Myth: his artificial nose was silver or gold. Fact: contemporary accounts mention precious metals, but chemical analysis of the remains suggests he wore a brass nose, at least at times.

Timeline

• 1546, 14 December: Tycho born at Knutstorp, Scania.
• 1566, December: loses part of his nose in a duel in Rostock.
• 1572, 11 November: observes the new star in Cassiopeia.
• 1576, 8 August: foundation stone of Uraniborg laid on Hven.
• 1577: observes the great comet.
• c. 1584: Stjerneborg built.
• 1588: publishes the Tychonic system.
• 1597: leaves Hven.
• 1600: Kepler joins Tycho near Prague.
• 1601, 24 October: Tycho dies in Prague.

Why it matters

Uraniborg showed that astronomy could be an organised, well-funded research enterprise with specialised instruments, trained staff and systematic records. The precision Tycho achieved there gave Kepler the evidence he needed, linking Copernicus’s idea of a Sun-centred system to the physics of Newton.