Tycho Brahe Observes a Supernova

Brahe’s observation of a supernova led him to develop new, precise instruments for observing and measuring the locations and movements of celestial bodies. Johannes Kepler used Brahe’s work to help demonstrate his radical theory that planets, including Earth, moved in ellipses around the sun.

Summary of Event

Tyge Brahe was born in Scandia, Denmark. His parents were Otto Brahe, a Danish nobleman, and Beate Bille, whose family included leading politicians and churchmen. Although Tycho was named Tyge at birth, he adopted the Latinized version of that name, Tycho, when he was about fifteen years old, and is generally known to astronomers as Tycho. His sister Sophie, the youngest of ten children and also an astronomer, was born when Tycho was a teenager. Astronomy;Denmark Brahe, Tycho Frederick II (1534-1588) Kepler, Johannes Brahe, Sophie Scultetus, Bartholomaeus Copernicus, Nicolaus Frederick II (king of Denmark) Kepler, Johannes Brahe, Tycho

In 1559, at age thirteen, Tycho enrolled at the University of Copenhagen to study rhetoric and philosophy, but he quickly developed an interest in astronomy. He observed an eclipse on August 21, 1560, and was particularly impressed by how precisely it was predicted. He soon became interested the methods used to measure the position and the motion of objects in the sky.

In 1562, Brahe was sent to the University of Leipzig to study law, a field he found difficult. So instead, Brahe moved to the study astronomy with Bartholomaeus Scultetus (Bartholomew Schultz). By August of 1563, Brahe began to record his observations, including the conjunction of Jupiter and Saturn, but he found that neither the astronomical data tables based on the work of Nicolaus Copernicus and of Ptolemy gave the correct date for this event. Brahe thought he could do better, so he was determined to make more-precise observations that could be used to develop better tables. Schultz taught Brahe how to make extremely accurate observations of the positions of stars and planets. Brahe knew that accurate observations required high-quality measuring instruments, so he began to acquire them during his stay in Leipzig. He also constructed his first astronomical instrument, the Jacob Stave, during this period.

In 1570, Brahe returned to Denmark, where he lived with his uncle, Steen Bille, who had founded the first paper mill and glassworks in Denmark. Brahe worked in the alchemy lab that Bille had established at Herreved Abbey. Bille was the only relative of Brahe who approved of his interest in astronomy, but Brahe devoted most of his efforts to alchemy Alchemy until November of 1572, when he observed an unusual object in the sky.

On November 11, 1572, as Brahe was leaving Bille’s alchemy lab, he noticed that a new star, one that he would call Stella Nova, had appeared in the constellation Cassiopeia, an experience that changed Brahe’s life. Brahe did not believe his eyes, so he called upon others to view the new star and to reassure him that it was really there. The new star, brighter than the planet Venus and observable during daylight hours, was visible for eighteen months. The object Brahe and the others had seen is known now as a supernova, a rare astronomical event defined as a stellar explosion that expels a star’s outer layers and fills the surrounding space with a cloud of gas and dust.

After Brahe’s observation, astronomers and philosophers began to ask, Where, exactly, was this new star located? Tradition had always taught that Earth was the center of creation, and that the objects in the sky were located on spheres that rotated around Earth. The stars were located on the outermost sphere, and both Aristotelian and Christian philosophy taught that the sphere of the stars had remained unchanged since the day of creation. In this view, it was not possible for a new star to appear in the perfect and unchanging sky.

The planets and the moon were known to move relative to the stars, so it was thought that this supernova was located either in Earth’s atmosphere or on one of the inner spheres, where the planets and the moon were located. If so, then the supernova would move relative to the stars, as did the planets and the moon.

Two leading astronomers, Michael Maestlin in Tübingen and Thomas Digges in England, tried to detect movement in the new star by lining it up with known fixed stars, using stretched threads to measure the separation. They saw no movement. Brahe, however, knew he could make more accurate measurements by using instruments that were built to precise standards and were much larger than those traditionally employed. Brahe had just finished building a new sextant, which had huge arms, 5.5 feet long. In addition, Brahe had developed a table of data allowing him to correct for the tiny errors in his sextant. Using this new sextant, Brahe determined that the new star did not move relative to the fixed stars. Thus, the new star was on the eighth, or outermost, sphere, a sphere that was not changing.

Brahe published a detailed account of his methods and results the next year. His book De nova et nullius aevi memoria prius visa stella (1573; better known as De nova stella De nova stella (T. Brahe) ; partial English translation in A Source Book in Astronomy, 1929) made him famous among astronomers throughout Europe. Other young noblemen asked Brahe to teach a course on astronomy, but he refused. He changed his mind only when the king asked him to teach. In September of 1574, Brahe began lecturing on astronomy at the University of Copenhagen.

In the spring of 1775, Brahe began a trip around Europe, visiting astronomers in many cities, including Frankfurt, Basel, and Venice. During his travels, Brahe decided to move to Basel. However, King Frederick II of Denmark did not want Brahe, recognized as the best astronomer in Denmark, to leave the country. So, the king offered Brahe the island of Ven (also known as Hven or Hveen), a 3-mile-long island on the sound between Denmark and Sweden and just off the coast of the storied castle of Shakespeare’s Hamlet at Elsinore. The king agreed to pay for the building of an observatory and a house on Ven, and the island’s inhabitants were to become Brahe’s subjects.

Brahe’s observatory, which was called Uraniborg, was equipped with instruments that allowed him to determine, much more precisely than had previously been possible, the positions of the stars and the planets. Brahe made astronomical observations during a twenty-year-period at Uraniborg, and he recorded each of these measurements meticulously. Brahe obtained particularly detailed measurements of the positions of Mars, which were so precise that they demonstrated that the orbit of Mars was not a circle but was actually an ellipse.

A new king, Christian IV, came to power in Denmark in 1588 and chose not to support Brahe’s astronomical efforts. Brahe moved to Prague shortly thereafter and was joined by a new assistant, Johannes Kepler. Upon Brahe’s death, all of his astronomical measurements were given to Kepler, who used them to develop his three laws of planetary motion.

Significance

Brahe’s observation of the supernova was significant for several reasons. First, it revived Brahe’s interest in astronomy after he had spent several years working on alchemy. Second, Brahe’s demonstration that this new star was truly a star overturned prevailing religious dogma, which stated that the heavens were perfect and unchanging.

Third, Brahe’s observations and De nova stella brought his work to the attention of the king of Denmark, who gave him the island of Ven and the income generated by its inhabitants to build and equip the Uraniborg Observatory. It was at this observatory that he obtained twenty years of critical astronomical measurements. As a result of the king’s support, also, Brahe was able to purchase or build the most precise instruments available to measure the positions of the stars and the planets, long before the invention of the telescope.

Finally, Brahe’s precise measurements of the positions of the planets in the sky provided the foundation for Kepler’s laws of planetary motion, which in turn were used by Isaac Newton to demonstrate the validity of his law of gravity over the astronomical distance scale.

Tycho Brahe Observes a Supernova Summary