Tycho Brahe was a Danish astronomer who was well known for his accurate measurements of the heavens. He saw the benefits of both the Copernicus model and the Ptolemy model. In 1588 he proposed a model that was a combination of the two. He assumed that the earth was stationary and was located at the center of the universe. The sun and the moon revolved around the earth. The other five planets revolved around the sun. Figure 9 shows his model (without epicycles).
It is not obvious, but it can be shown that Tycho Brahe's model is mathematically equivalent to the Copernicus model. Therefore, they have the same accuracy. The model of Tycho Brahe had the advantage of being consistent with Ptolemy's intuitive arguments for a stationary earth. Thus, at this point in history, belief in an earth-centered universe was still a very rational position. Let us look briefly at the man behind this model.
Tycho was born on December 14, 1546 to Otte and his wife Beate in the family manor, Knutstorp Castle (then in Denmark but now part of Sweden). A picture of this manor is shown in Figure 10. His birth name was Tyge, but he would later go by the latinized name Tycho (pronounced Tee-ko).
Tycho's parents were part of the Danish aristocracy. Tycho was the second born of twelve children. He was very close with his younger sister Sophia who later assisted him in some of his experiments. In 1549, when Tycho was two years old, he was kidnapped from his home by his paternal uncle Jorgen. It turns out that Otte had once drunkenly promised his childless brother one of his children. Jorgen felt that it was now time to collect. Although Otte was upset, he never sought the return of Tycho. Tycho's new parents were also members of the Danish aristocracy. Thus Tycho never had to worry about finances.
When Tycho was 12 years old he was enrolled in the University of Copenhagen (This was not unusual at the time). Following his parents' wishes he majored in law and philosophy. In August of 1560 he witnessed a solar eclipse that had been accurately predicted by the astronomers. He was fascinated that they could accurately predict an event such as this in advance. This was probably the beginning of his passion for astronomy.
Unknown to his parents, Tycho lead sort of a double life while in college. In the daytime he concentrated on subjects related to the major chosen by his parents. In the evening he spent his time reading books on astronomy and making observations of his own. His deception was aided by some of his professors who provided him with books and observation devices. When his parents found out, they moved him to the University of Leipzig in Germany. For the next three years, his curriculum was restricted to courses in law and philosophy, as well as some standard science and mathematics. Brahe's parents employed a 20-year-old Dane to keep watch over him. However, Tycho still managed to secretly continue his study of astronomy. At age 16 he built a device called a Jacobs-staff to measure the angle between stars. This device is pictured in Figure 11.
It consists of a long piece that is marked like a ruler. The cross piece slides along the long piece. It is moved so that when viewed from the end of the long piece it just fills the gap between the two stars. The angle can be determine knowing the length of the cross piece and the position of the cross piece along the long piece. He also used a standard drafting compass to measure angles. He positioned his eye behind the center of the compass and pointed the legs of the compass at the two different stars.
In August of 1563 Tycho began to keep a log of his observations, He soon began to see errors in many of the published star charts. He came to believe that there was a need for a series of measurements from the same location over a period of years. One of the most glaring discrepancies involved the prediction of the conjunction of Jupiter and Saturn that occurs about every 20 years. The predictions by various astronomers differed widely with some off by months. In September he actually witnessed this conjunction which occurred far ahead of predictions. This motivated Tycho to continue with his observations.
In May of 1565 Tycho took a break and returned home. About a month after his return his father died. Jorgen had been riding with King Frederick II when the king's horse became spooked and threw the king off into the river. Jorgen dived in to the icy waters and rescued the king. Unfortunately, Jorgen contracted pneumonia that lead to his death. The king was very grateful and would later offer assistance to Tycho. Since Tycho was several months shy of his eighteenth birthday, he was considered a minor and his custody was returned to his birth parents Otte and Beate.
Although Tycho's birth parents desired for him to pursue a career in line with their position, they did not make it mandatory. Tycho ignored their wishes and pursued his studies and observations in astronomy at several universities. While at Rostock He and a fellow student had too much to drink and after a disagreement decided to settle it in a duel. In the duel the other student accidentally cut off most of Tycho's nose. Tycho later shaped a piece of brass to replace his nose. He painted it to match his skin color and held it place with paste. Hereafter he always carried paste so he could make repairs. Tycho spent the next several years furthering his education in astronomy and conversing with other astronomers on how to make better observations.
Near the end of 1570 Tycho went home to be with his father who was dying. Otte died on May 9, 1571. Tycho inherited a large sum of money as well as his birth home Knutstorp Castle. Tycho decided to not live there, but instead went to live with his uncle Steen Bille in the former Monastery of Heridsvad. His uncle along with his sister Sophia were the only family members who supported his ventures into astronomy. To show support for his nephew uncle Bille financed the construction of an observatory on the monastery grounds.
In the early months of 1572 Tycho became romantically involved with a childhood friend Kirsten Jorgensdatter. They wanted to marry, but that would require Tycho to give up all his noble privileges since Kirsten belonged to a lower class. Instead they lived together unwed for three years at which point they were considered married by common law.
In November of 1572 Tycho discovered a brilliant star in the constellation Cassiopeia that was not there previously. He tracked the star for months using a new sextant he had built. He determined that the star must be beyond the moon since it behaved like the fixed stars. This new star is now called ‘Brahe's Supernova.’ In 1573 he published a book on this new phenomena entitled De nova stella.
Figure 12 below shows a sextant like Tycho used at his observatory to measure the angular elevation of a star or planet. The sighting bar can be rotated along a 60° arc. The top of the arc and the end points of the bottom bar are vertices of an equilateral triangle. Thus, the bottom bar is level if a plumb line from the top of the arc bisects the bottom bar.
In 1574 Tycho was appointed Official Astronomer of Denmark, a title he held for over two decades. King Frederick II also gave Tycho the island of Hven and provided funds for a large mansion and observatory on the island. Tycho constructed a large castle on the island which he called Uraniborg. He also constructed a fully equipped observatory nearby. Figure 13 shows Tycho's Uraniborg castle.
The observatory contained a variety of devices, including a large mural quadrant having a radius of 165 cm. (5.41 ft.). This quadrant was used to accurately measure a star's elevation. The quadrant was built into a wall and centered on an open window. A quadrant is similar to a sextant except that it uses a 90° arc instead of a 60° arc. Figure 14 shows an artist's illustration of a quadrant.
Tycho also had a number of accurate time pieces so that measurements could be made at the same time every night. He also had the staff and equipment in order to make four simultaneous measurements of the same object. The standard accuracy of measurements prior to this time was 10 minutes of arc. Tycho was able to lower this accuracy to one minute of arc or less. One of his most trusted assistants was his sister Sophia.
In 1588 Tycho introduced his earth-centered model in which the sun and moon orbit the earth and the other planets orbit the sun. A complete description of his system was contained in his book entitled De Mundi Aetherei Recentioribus Phaenomenis Liber Secundus (The Second Book About Recent Phenomena in the Celestial World). In April King Frederick II died and his successor King Christian IV was less willing to continue the support of Tycho's projects. After years of negotiation Tycho had to close his observatory in 1597. He was stripped of his title as the Official Astronomer of Denmark.
Tycho didn't stay unemployed long. In 1599 he moved to Prague and was appointed “Imperial Mathematicus and Official Astrologer” by the Holy Roman Emperor Rudolf II. It was in Prague that Tycho teamed with Johannes Kepler. We will look at Kepler and his life later on.
Tycho died in October, 1601. He collapsed in pain at a party and died 11 days later. An autopsy was not able to pinpoint the cause of death. There have been many conspiracy theories claiming that Tycho didn't die of natural causes. Some even thought that he was murdered by Kepler. His body was exhumed in 1901 and examiners found traces of mercury. His body was exhumed again in 2010 and Czech scientists determined that the amount of Mercury in Brahe's body was not lethal. They concluded that Tycho died of an acute bladder infection.