Tycho Brahe

• 1. Introduction

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  Tycho Brahe was born on the 14th of December 1546, into one of Denmark's most powerful noble families, and he died having mapped the sky more precisely than any human before him. On the night of the 11th of November 1572, he stepped outside Herrevad Abbey and saw something that should not have existed: a star blazing in the constellation Cassiopeia, far brighter than anything beside it, in a sky that ancient philosophy declared eternally fixed and unchanging. That moment did not just change his career. It helped crack open the entire medieval picture of the cosmos.

  He was, at various points in his life, an astronomer, an astrologer, an alchemist, a feudal lord, an exile, and a man who wore a prosthetic nose made of brass for the better part of three decades. He built the first large observatory in Christian Europe on a small island between Denmark and Sweden, employed nearly a hundred students and craftsmen, kept a tame elk, and hosted a Scottish king who later wrote him a poem. He died in Prague in 1601 at the age of 54, having refused, at a formal banquet, to leave the table to relieve himself. His data outlived him in ways he barely anticipated: within a generation, Johannes Kepler used his meticulous records of Mars to derive the three laws that govern planetary motion to this day.

• 2. Noble Blood, Unconventional Life

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  Both of Tycho's grandfathers and all four of his great-grandfathers had served on the Danish king's Privy Council. His paternal grandfather, Thyge Brahe, was lord of Tosterup Castle and died in battle during the 1523 Siege of Malmö. His maternal grandfather, Claus Bille, took part in the Stockholm Bloodbath on the side of the Kalmar Union king. The family's reach into Danish power was total, and from birth Tycho was positioned to follow that path into law and politics.

  At age two, however, he was taken from his parents and raised by his uncle Jørgen Thygesen Brahe and aunt Inger Oxe, who were childless. He moved between several estates, including Tosterup, Tranekær on Langeland, Næsbyhoved Castle near Odense, and the Castle of Nykøbing on Falster. Tycho later wrote of Jørgen Brahe: "He raised me and generously provided for me during his life until my eighteenth year; he always treated me as his own son and made me his heir."

  At age 12, on the 19th of April 1559, Tycho enrolled at the University of Copenhagen to study law, per his uncle's wishes. A solar eclipse on the 21st of August 1560 captured his imagination. The eclipse had been predicted, but the prediction was a full day off. Tycho grasped immediately that astronomy could only advance through more precise observation, and he began buying books on the subject. His uncle, wanting a civil servant, sent him in early 1562 on a study tour of Europe under the supervision of the 19-year-old Anders Sørensen Vedel. Tycho was 15. He talked Vedel into letting him pursue astronomy instead.

  At the Lutheran Leipzig University, Tycho observed a close conjunction of Jupiter and Saturn in 1563 and found that both the Copernican and Ptolemaic tables used to predict it were wrong. That failure convinced him that progress required rigorous, nightly observation with the most accurate instruments available.

• 3. A Nose Lost in Darkness

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  On the 29th of December 1566, at age 20, Tycho lost the bridge of his nose in a sword duel fought in the dark. His opponent was Manderup Parsberg, a fellow Danish nobleman and his third cousin. The quarrel had begun nineteen days earlier at an engagement party at the home of Professor Lucas Bachmeister, where the two had drunkenly argued over who was the superior mathematician. The cousins later reconciled, but the physical damage was permanent.

  For the rest of his life Tycho wore a prosthetic nose, kept in place with paste or glue and long assumed to be made of silver and gold. In November 2012, Danish and Czech researchers who chemically analyzed a bone sample from the exhumed body reported that the prosthesis was actually made of brass. He also carried a broad scar across his forehead from the encounter.

  The duel occurred while Tycho was studying at the University of Rostock, where he had also become interested in medical alchemy and herbal medicine. His later work at Uraniborg would blend these interests with astronomy; the observatory's basement held a full alchemical laboratory with 16 furnaces for distillation experiments. His herbal medicines, made from a garden at Uraniborg, were reportedly used in treating fever and plague and remained in use until the end of the 19th century.

• 4. The Island Observatory

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  King Frederick II offered Tycho the island of Hven in 1576, after learning that the astronomer was secretly planning to move to Basel. The island sat in Øresund between the provinces of Zealand and Scania, and its 50 families had previously considered themselves freeholding farmers. Under Tycho's appointment as feudal lord, that changed. He required them to cultivate twice as much as before and exacted unpaid labor for the construction of his new complex. The peasants took him to court. The court upheld Tycho's right to levy taxes and labor, and a formal contract was drawn up.

  The building Tycho envisioned was named Uraniborg after Urania, the muse of astronomy. Construction began in 1576. It drew on the Venetian architect Andrea Palladio's designs, making it one of the first structures in northern Europe to show influence from Italian Renaissance architecture. The basement contained the alchemical laboratory with 16 furnaces. The observatory also held a printing press and a paper mill, both among the first in Scandinavia, which Tycho used to publish his own manuscripts on locally made paper bearing his own watermark. He built a system of ponds and canals to drive the paper mill's wheels.

  When Tycho found that Uraniborg's towers were too exposed to wind and the movement of the building, he constructed an underground observatory nearby in 1584 called Stjerneborg, or Star Castle. Its hemispherical crypts held major instruments including a great equatorial armillary, a large azimuth quadrant, a zodiacal armillary, the largest azimuth quadrant of steel, and the trigonal sextant. Mounting them directly on bedrock eliminated the instability he had identified in the towers above.

  Nearly 100 students and artisans worked at Uraniborg between 1576 and 1597. One permanent resident was a man with dwarfism named Jeppe, whom Tycho believed could predict whether ill people on the island would recover or die. Among the scientific alumni who passed through were Christian Sørensen Longomontanus, who later became Tycho's replacement as royal Danish astronomer, Peder Flemløse, Elias Olsen Morsing, and Cort Aslakssøn. James VI of Scotland, who had married the Danish princess Anne, visited Hven in 1590 and afterward wrote a poem comparing Tycho with Apollon and Phaethon.

• 5. The New Star and the Comet

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  On the 11th of November 1572, Tycho observed what he called a stellae novae from Herrevad Abbey: a new star in Cassiopeia, now catalogued as SN 1572 and located roughly 7,500 light-years from Earth. Aristotelian philosophy held that the heavens beyond the Moon were perfect and unchanging. Other observers assumed the object must be something in the atmosphere below the Moon. Tycho measured it differently. He found no daily parallax against the background of fixed stars, meaning it lay farther away than the Moon. And unlike any planet, it did not shift position against the fixed stars over several months.

  His 1573 publication De nova stella coined the term nova for new stars, and his claim that the object was a fixed star in the stellar sphere contradicted one of the foundational axioms of medieval cosmology. He was blunt about those who dismissed the evidence, writing in the preface: "O crassa ingenia. O caecos coeli spectatores" - roughly, "O thick wits. O blind watchers of the sky." The publication made his name across Europe.

  Five years later, the Great Comet of 1577 gave him a second opportunity to dismantle the old worldview. The comet was visible in the northern sky from November 1577 to January 1578. Many Danish amateur astronomers published predictions of apocalypse. Tycho measured the comet's distance as far exceeding that of the Moon, ruling out an atmospheric origin, and estimated its closest approach to Earth at about 230 times the Earth's radius. He calculated that its orbit likely fell between Mercury and Venus.

  That placement was devastating for the ancient model of solid celestial spheres. If the comet traveled between Mercury and Venus, it had to pass straight through any rigid sphere that might carry those planets. Tycho also noted that the comet's tail always pointed away from the Sun. His predictions from the comet included bloodshed in Moscow and the fall of Ivan the Terrible by 1583.

• 6. The Tychonic Model

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  Tycho admired Copernicus and was the first to teach the heliocentric theory in Denmark, but he could not accept it. He believed the Earth was far too massive and sluggish to be in constant motion. Aristotelian physics held that the heavens were made of aether, a substance that caused objects to move in circles, while objects on Earth naturally came to rest. To Tycho, the idea of a moving Earth was "in violation not only of all physical truth but also of the authority of Holy Scripture, which ought to be paramount."

  He also had a geometric objection. If the Earth orbited the Sun, the apparent positions of stars should shift measurably every six months as the Earth moved from one side of its orbit to the other. No such parallax was visible. Copernican astronomers explained this by arguing that the stars were simply too distant to show any shift. Tycho used geometry to show that, at those required distances, each ordinary star would have to be at least as large as the entire orbit of the Earth around the Sun, vastly larger than the Sun itself. His Copernican correspondent Rothmann responded that this absurdity was no absurdity at all: God could make his creations as large as he wished.

  Tycho's answer was the Tychonic model, formally developed in 1587. In it the Sun and Moon orbit a stationary Earth, while all other planets orbit the Sun. The model preserved the mathematical advantages of Copernicus while keeping the Earth at rest. It also eliminated solid celestial spheres entirely, a point supported by both his comet observations and the intersecting orbits of Mars and the Sun that his system required.

  The Tychonic model gained particular traction after 1616, when the Catholic Church declared heliocentrism contrary to scripture. Supported by Jesuit writers, the model spread as far as China through the work of Longomontanus, whose 1622 Astronomia Danica was considered the canonical statement of the complete Tychonic system. As late as 1728, the astronomer Francesco Blanchinus described it as the commonly accepted system.

• 7. Exile and Death in Prague

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  King Frederick II died in 1588. His son Christian IV was 11 years old, and a regency council under Christoffer Valkendorff took control. Valkendorff had a personal grievance against Tycho, and the astronomer's influence at court declined steadily. Tycho was also known to sympathize with the Philippists, followers of Philip Melanchthon, which made him politically suspect to the gnesio-Lutheran bishops around the new king. Accusations mounted: failure to maintain the royal chapel at Roskilde, exploitation of the Hven peasantry, the practice of medicine and alchemy without church approval, and a personal prohibition on the local priest including exorcism in baptisms.

  A mob, possibly incited by his court enemies, rioted outside his house in Copenhagen. He left Hven in 1597, taking some instruments and leaving others with a caretaker. Shortly before departing, he completed a star catalogue listing the positions of 1,000 stars. He spent about a year at the castle of his friend Heinrich Rantzau near Hamburg, then moved briefly to Wittenberg, to the former home of Philip Melanchthon himself.

  In 1599, Rudolf II, Holy Roman Emperor, gave him patronage, and Tycho settled in Prague as Imperial Court Astronomer. He built a new observatory at Benátky nad Jizerou, 50 km from Prague. The emperor then brought him back to the city. At the imperial court, his wife Kirsten and their children were treated as nobility, something they had never been granted in Denmark.

  In Prague, Johannes Kepler joined him in the last year of his life. Tycho died on the 24th of October 1601, eleven days after he fell suddenly ill at a banquet. Kepler's first-hand account states that Tycho had refused to leave the table to relieve himself, considering it a breach of etiquette. He later suffered extreme pain and was almost unable to urinate. The night before he died, he was heard repeatedly to exclaim that he hoped he would not seem to have lived in vain. He is buried in the Church of Our Lady before Týn in Old Town Square in Prague, near the Prague Astronomical Clock.

• 8. What He Left Behind

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  Kepler called Tycho the new Hipparchus, the astronomer who would provide the foundation for a restoration of science. That proved accurate. Using Tycho's records of Mars, Kepler derived his three laws of planetary motion. From those records also came the Rudolphine Tables, published in 1627, which calculated planetary positions with unprecedented accuracy and helped establish the heliocentric model as the basis of modern astronomy.

  Tycho's star positions, compiled at Uraniborg and Stjerneborg, were the most accurate of any pre-telescopic astronomer. His measurements approached one arcminute in accuracy, about five times better than those of his closest contemporary, Wilhelm of Hesse. He published the first systematic tables for correcting atmospheric refraction, the distortion that makes celestial objects near the horizon appear higher than they actually are. To handle the volume of calculations his work required, he relied heavily on prosthaphaeresis, a then-new trigonometric technique that predated logarithms.

  His lunar theory doubled the number of known lunar inequalities, reducing discrepancies in lunar calculations to about a fifth of their previous amounts. It was published posthumously by Kepler in 1602.

  The Tycho Brahe Prize, established in 2008 by the European Astronomical Society, is awarded each year in recognition of pioneering work in European astronomical instrumentation. A lunar crater, a crater on Mars, and the minor planet 1677 Tycho Brahe in the asteroid belt all carry his name. In 2015, the planet Brahe was named after him through the NameExoWorlds campaign. The first full-length biography of any scientist was the biography of Tycho, written by Pierre Gassendi in 1654.