Tycho Brahe is a forgotten man. When we think of great astronomers of the past, Nicholas Copernicus, Johannes Kepler, and Galileo Galilei come to mind quickly. But what about the Dane, Tycho Brahe? Most amateur astronomers have a hard time naming his greatest accomplishments.

Despite this, Tycho was one of the all-time greats in science. He was the first full-time astronomer, founding the great observatories Uraniborg and Stjerneborg and providing them with equipment that for its time was on the cutting-edge of technology—sextants, armillary spheres, and quadrants. Tycho was the first to apply what we think of as modern systematic and qualitative observation to astronomy. He provided the first logical basis for determining relative cosmic distances and disproved ancient, primitive conceptions of comets and celestial space. And he laid the groundwork for the triumph of the Copernican revolution because he meticulously plotted solar, lunar, and planetary motions.

Born To Be an Astronomer?

The eldest of eleven children of Otto Brahe, Tycho was born on December 14, 1546, at the family seat of Knudstrup in Scania. His youth was relatively comfortable. Under a family agreement, his childless uncle Jörgen acquired the responsibility for educating young Tycho. By the time he was a teenager, Tycho was sent by his uncle to the University of Copenhagen and to Leipzig to study for a career in statesmanship.

The sudden death of his uncle in 1565 gave Tycho the freedom to pursue his own education. The most painful event at school didn't involve books, however. On December 29, 1566, Tycho sought to resolve a disagreement with another Danish nobleman by duel. The two fought with swords, and Tycho lost part of the bridge of his nose. He subsequently patched the wound with a waxy form inlaid with gold and silver. Thereafter, he carried a box of salve, frequently applying the medication to his sore nose.

Classical studies and a solar eclipse in 1560 turned Tycho's attention toward the stars. In his school days, Tycho became acutely aware of the need for accurate observations with instruments superior to the current tools used by astronomers. Naked-eye instruments, little changed from ancient times, were used as positional plotting tools. The most common instruments were a graduated arc limb with partial or full circumference and a radial ruler (alidade) with a sight at each end. The quadrant (90° arc) and the early sextant (60° arc) used by both mariners and astronomers were based on the earlier two-armed compass. These tools were used to measure angular dimensions in the sky or altitudes of celestial objects.

Other tools were somewhat more sophisticated. These included rings and armillary spheres. An armillary sphere was a globe-shaped device that provided a threedimensional representation of the heavens as a celestial sphere, with Earth at the center. By including lines representing the celestial equator, the ecliptic, and the latitude and longitude, an astronomer could use an armillary sphere to study stars and planets relative to celestial space rather than the Earthly horizon.

These instruments served 16th-century astronomers well, but Tycho wanted to improve them. He wasn't satisfied with being a mere participant; he wanted to innovate. Tycho realized that he could gain more accuracy in his instruments by making them bigger. He set about building large versions of his instruments during the next stage of his life. He realized two key qualities for building large instruments: Graduated angular scales had to be made accurately enough to subdivide degrees into arcminutes. He also realized the need to correct for parallax and atmospheric refraction.

In 1568 Tycho built a quadrant with a radius of 14 cubits (21 feet) at Augsburg. The quadrant was so heavy that it required twenty men to set up. The quadrant pivoted at the intersection of its two arms by means of a massive beam placed vertically in a cubical wooden frame. This made it possible to sight along the arm and move the limb, which was graduated to ten-arcsecond intervals, to indicate degrees of altitude. This instrument was used in the open until 1574, when it was destroyed in a storm.

Having gained valuable experience with equipment construction and use, Tycho returned to Denmark late in 1570. On the night of November 11, 1572, his life was dramatically changed. That evening he went outside to watch the sky over Heridsvad Abbey, and he saw a star as bright as Venus in the constellation Cassiopeia. By coincidence he had just finished building a 60° sextant of walnut about five and a half feet long in the arms. This time Tycho made the eyepiece with a vertical slit for aligning the star precisely with the top of the object sight and positioned it with a hand crank. The workmanship of this fine sextant allowed him to plot the position of his new star accurately.

The new star was what we know today as a supernova. Tycho measured its angular distance from the stars of Cassiopeia in order to plot the supernova's celestial latitude and longitude. He noted as time passed that the supernova's coordinates did not change relative to the stars. Tycho published an account of the new star in late 1573, and the star finally faded from naked-eye visibility in March 1574. Tycho's supernova allowed him to accomplish two big breakthroughs: he showed that the heavens were changeable (which Aristotle had denied), and he concluded that the new star was as distant as the ordinary stars, because it had no detectable parallax.

Think I'll Build a Castle

Discovering the new star changed Tycho's attitude about astronomy. He now saw himself as completely devoted to the subject. Probably thinking of the repercussions of the astronomer's reclusive life he would now pursue—not the thing for a noble lady—he married a commoner named Christine. She eventually bore him eight children.

Tycho's fame caused by the supernova discovery resulted in an acquaintance with the king of Denmark. In February 1576, the king told Tycho that he could forget courtly duties and accept a life of isolation more suitable for his astronomical pursuits. Tycho moved to the little island of Hven, situated in the sound between Elsinore and Landskrona, in Scania. Funds would be forthcoming to build a great house, and the king let Tycho know that the island and its inhabitants were Tycho's for life. At that time Hven was sparsely populated by tenant farmers. Consisting of a bare 2,000 acres, it was the perfect spot to erect a monument to stargazing. Tycho decided to build a great observatory and call it Uraniborg, Castle of the Heavens.

Uraniborg was no medieval castle of thick gray walls, but a mixture of Renaissance styles. Tycho was already making observations from unfinished quarters in December 1576, although the structure was not completed until 1580. Made of red brick with sandstone ornamention, the central residence measured 49 feet square and was 37 feet high. An octagonal pavilion was topped by an onion dome with clocks and a gilt weather vane in the shape of Pegasus.

The north and south ends of Uraniborg housed two observation turrets 18 feet in diameter and 18 feet in height. Platforms were located at the top. The roofs were cone-shaped, comprised of hinged triangular sections of wood that could be folded back for observing any part of the sky. At the outer end of each of these were two small observation towers on single pillars, sporting the same sort of roof and connected by galleries and catwalks to the platform levels of the large parent turrets.

Gardens and orchards spread out 248 feet on all sides of Uraniborg and were enclosed by earthen walls 18 feet high and 16 feet thick at the base. Within the pavilion was an octagonal room with a ceiling clock and a wind indicator connected to the weather vane outside—a means of anticipating possible wind problems for the instruments. Below this, above the second-story rooms, were eight small rooms or garrets for student astronomers.

The ground floor comprised two large guest rooms, a family sitting room, and a study. The south observatory turret had a ground-floor library for study and a basement chemical laboratory. The northern observatory housed the kitchen at the ground level and a well in the basement, which provided pumped water to the floors above. Tycho's collection of instruments, often reworked at extra cost until made correctly, began to fill Uraniborg.

The observatory's library housed a great celestial globe five feet in diameter and covered in brass plates that Tycho had commissioned on his trip to Augsburg in 1570. On this globe, Tycho had his own goldsmith, Hans Crol, engrave celestial, equatorial, and zodiacal circles graduated in minutes and the positions of several hundred stars.

Uraniborg's study contained one of Tycho's most important instruments, a mural quadrant. The mural quadrant was a meridian instrument—that is, it was fixed in place on the south wall to await stars or the Sun ascending across its position, as seen through a square window cut in the wall. The graduations were marked off to ten-arcsecond intervals. For the convenience of low- or high-angle observing, two large sights could slide along the arc and were aligned with a star along a brass cylinder inserted outside the window.

Tycho was proud of this instrument and considered it an original idea. A few such quadrants had existed before Tycho's, but Tycho's was far superior. He used it as a means of showcasing Uraniborg. The observer sighted a star for altitude and called it out to the recorder. For transists across the meridian, the observer also sighted through the left slit, calling out the start of the observation to a third observer who marked the time on interregulated minute and second clocks. After the star crossed the meridian and appeared in the right slit, its position and transit time were noted as well.

The instrumentation on the rooftop observatory turrets was an impressive collection that included equatorial armillaries, four quadrants with graduated azimuth rings for altitude and azimuth positioning of stars and time determination, and a two-observer double brass and iron arc.

One Just Isn 't Enough

By 1584 Uraniborg felt cramped. So Tycho constructed a second observatory on a small rise about a hundred feet south of the perimeter of Uraniborg. This was called Stjerneborg, or Castle of the Stars. This facility was comprised of a wooden enclosure 57 feet square housing five observing rooms and a central study with a brass mechanical statue of the god Mercury rotating at the top.

Stjerneborg's study and its three contiguous circular rooms were essentially subterranean crypts designed to protect observing instruments from wind. The crypts were supplied with circular ramps for descending and ascending along the exterior of the instruments employed at Stjerneborg. The largest of these observation rooms was built with a dome and capital like Uraniborg's. The dome was made of triangular wood segments that could be removed as necessary. This crypt housed Tycho's largest instrument, a great equatorial armillary composed of a huge, revolving iron declination ring nine feet across fitted with two sights and strutted for stability to a tubular steel axis with a brass objective cylinder sight at its center.

The other two subterranean rooms were supplied with ground-level, special-beamed, doubled skylight roofs equipped with circumferential wheels. The left room held a ten-foot diameter quadrant. The right room held a 12-foot diameter steel quadrant. These instruments joined the mural quadrant as principal tools for star transits and for determining solar orbital motion from altitude and declination observations.

Uraniborg was not only a working observatory; it was an astronomy school. Tycho felt that observing assignments given to many observers and then averaged together would provide the most reliable data. This was required for all of the stellar, lunar, solar, and planetary observations made at both of the observatories.

Employing this impressive array of instrumentation for nearly twenty years, Tycho trained observers and computers. He filled the meteorological diary and his data ledgers with plots showing solar, lunar, stellar, and planetary data. Tycho's solar observations allowed him to calculate a table of refraction corrections for each degree of altitude. From the lunar data—distances from fixed stars, altitudes, and declinations—Tycho discovered anomalies in lunar orbital motion. But lacking the gravitational theory that Isaac Newton would develop one hundred years later, Tycho could not completely account for them.

One outstanding area of neglect in Tycho's time was creating a star catalog. The basic job done by Hipparchus was then more than 1,600 years old. Using a mean value for the right ascension of Alpha Arietis as a base star, Tycho determined the positions of the nine brightest stars and twelve others close to the zodiacal circle. Between the years 1578 and 1591, he used these data to determine the right ascensions of all other prominent naked-eye stars, 777 in all.

In addition to the supernova of 1572, Tycho and his assistants carefully observed positions and parallaxes of comets that appeared in 1577, 1580, 1585, 1590, 1593, and 1596. The comet of 1577 provided Tycho with his first solid physical data since the supernova to suggest serious flaws in the ancient model of the cosmos. In tracking this comet (particularly with the oneobserver sextant), Tycho saw no appreciable diurnal parallax. This meant the comet cut a path through the heavens that lay beyond the Moon and must, in fact, travel through the orbits of the planets. The other cometary data reinforced his important findings and helped to define a new cosmos.

Tycho's study of cometary trajectories proved that the Aristotelian theory of crystalline planetary orbital spheres was impossible. And he demonstrated that comets move in celestial space and are not products of earth's atmosphere. The importance of this is incalculable. It thrust astronomy forward as a modern conception for the first time. Prior to that it had roots deeply planted in unscientific thought. In one series of arguments Tycho succeeded in liberating fundamental ideas about the universe that would echo throughout future astronomy and set the stage for the eventual success of the Copernican revolution. (Ironically, Galileo still believed that comets were part of Earth's atmosphere, while Kepler could not shake off solid, geometrically arranged celestial spheres. Both were contemporaries of Tycho.) Change was a slow process, however—elder astronomers continued to try to explain away any physical data contrary to ancient conceptions.

Unfortunately Tycho did not oversee Hven carefully, being distracted by his intense astronomical work. He put off duties such as repairing buildings and treated some of his tenants with a snobbish arrogance. Consequently, though King Frederick II overlooked complaints, Tycho's brash and stubborn behavior came home to roost after the king's death in 1588. Royal cutbacks came with the new king, Christian I, and Tycho's pride over the importance of his work and resentment of criticism kept him from making apologies and compromises. This deterioration of relations precipitated Tycho's departure from Hven and his native land. He had made an insignificant island into the showpiece of Renaissance science. But Tycho had also grown tired of his isolation and wished for greater opportunities.

In 1597 Tycho packed up his family and all but the four largest instruments and made his way to Rostock with the intention of becoming Imperial mathematician for Emperor Rudolf II in Prague. The bulk of instruments and books was stored at Magdeburg, while the remaining instruments at Hven were shipped to Lübeck and then forwarded to Hamburg for shipment down the Elbe. Meanwhile, Tycho took up residence in the imperial castle Benatky, where he planned to recreate a Uraniborg-style observatory and laboratory. But instead Tycho drifted back to Prague. Desperately in need of a colleague, Tycho discovered the man who would fall heir to his legacy, Johannes Kepler. The two were not strangers. Kepler had already published his first book in 1596 on the Copernican system and was known by Tycho.

Tycho had always shown an affection for Kepler and he now expressed enthusiasm for Kepler's assistance. Kepler came to Prague in January 1600, but his right to the wealth of lunar and planetary observations, which no one was more qualified to examine and decipher, was in doubt until he was treated as an equal. Kepler grew eager for full access to Tycho's life's work, for Tycho was showing signs of approaching old age, which might complicate timely research.

Barely a year later Tycho died, suffering a stroke at the dinner table on October 13, 1601. With his family and close associates at his bedside, Tycho lingered for ten days before succumbing. Tycho had entrusted to Kepler his life's observations and asked him to complete a logical planetary theory. Of course Kepler went on to great success, determining the laws of orbital motion. Tycho's influence resonated not only in Kepler but throughout the lives and thoughts of all astronomers to come. And what of Uraniborg and Stjerneborg? Hven changed hands in 1602, 1616, and in 1645. A new dwelling called Kongsgaarden was erected from Uraniborg bricks. In 1671 the foundation of Uraniborg was still visible, though Stjerneborg was but a hollow in the ground.

During the 19th century, antiquarians unearthed the Uraniborg laboratory and the three crypts at Stjerneborg. Simple markers indicate the location of Uraniborg today. One would hardly think that 400 years ago on that deserted spot lay the world's first scientific observatory and one of the great centers of free thought for humanity. Because he established the foundation of modern astronomy, it's difficult not to feel the contributions of the lord of Hven, Tycho Brahe.