The texts about the instruments are brought from Arne Wennberg's "Tänk, om det är så : om Tycho Brahes instrument och vad han kunde göra med dessa" (1996), with the permission from the author.
Tycho's smallest quadrant

Tycho's smallest quadrant (1573)
This is one of Tycho's early instruments, and his first quadrant.. It had a radius of about 39 cm and was made of gilt brass. The instrument was used for determining altitudes. It was provided with Nonius' (see next page) scales for accurate readings. The quadrant was not used very often. It was mostly referred to because of a little piece of art painted on it. It represented a tree, on the left-hand side, with green leaves and green grass under it. On the right-hand side, the tree had dead roots and withered branches. In the grass a youth was sitting. He was wearing a laurel-crown and held in his hands a book and a star-globe. Under the tree's withered branches a table was standing, filled up with various things representing richness and abundance. A skeleton was leaning against the table trying to grasp the precious things. Above the picture was a pentameter in Latin, saying that only studies and knowledge can give immortality. Richness and wealthiness are all in vain. The instrument was later moved and kept in the Stjerneborg observatory.
The medium sized quadrant (1580)

This instrument was made of solid brass. It was used for determining altitudes, but was also equipped with a horizontal circle with a scale for reading azimuths. It had a radius of 58 cm. This instrument, as well as the minor quadrant and one sextant, was provided with a system of supporting scales for easy and accurate readings. That system emanated from a Portuguese mathematician and astronomer, Pedro Nunez (Latin Nonius, 1492-1577). It was, theoretically, an elegant way to get good readings but it was practically very difficult to engrave all these arcs perfectly. This instrument was also furnished with Tycho's own transversal division, another system to help the observer to make exact readings of angles. Tycho had once learned this system in his youth in Leipzig, and developed it. He very soon abandoned Nonius' system for his own system. The instrument was placed in the larger southern observatory of Uraniborg.
Another quadrant of brass

This quadrant is functionally very similar to the one described before. It was made of genuine brass and had also a radius of 58 cm. It also had an azimuth circle cast in solid brass of 117 cm in diameter. This instrument had neither the Nonius nor the transversal system for reading. It could be read to an accuracy of one minute. The instrument had a very light construction and could easily be dismounted and taken along on journeys. The instrument was placed in the larger southern observatory of Uraniborg.

What is meant by a quadrant is a quarter of a circle; a sector covering 90 degrees. In the same way, a sextant is a sixth of a circle; 60 degrees, and an octant is an eighth of a circle; 45 degrees.
The astronomical sextant for altitudes

Sextants were favourite instruments of Tycho. They were used both to determine altitudes and to measure distances between stars. This is one of three sextants of about the same size that Tycho built. It was placed in the southern larger observatory in Uraniborg. The instrument was probably made of wood, but cleverly covered with brass plating and it looked as if it was made of solid brass. The limb and the sights were also made of brass. The radius was 155 cm. This sextant hung on a pillar and was turnable only in the vertical plane. Thus, only altitudes could be measured with this instrument. When altitudes were to be measured, the instruments upper leg had to be exactly horizontal. To achieve this, a plumb line was used. The instrument was rather light and could be taken apart and remounted in another place.
The great mural quadrant (1582)

This was one of Tycho's most important instruments and, at the same time, probably the most simple to understand. It consisted of a solid brass arc, a quarter of a circle, mounted directly on the wall. It was placed on the west wall in the southwestern room of the castle. The instrument was carefully adjusted to the meridian's plane; the north-south direction. On the arc, there were two sliding sights. In the southern wall, close to the ceiling, there was a little hole with a cylinder of gilt brass. The observer slid the sight until he saw the star in line with the cylinder. If the sun was to be observed, the shadow of the cylinder was caught on the sight. With this instrument, Tycho could determine the meridian altitudes of the heavenly bodies. He could also find out the time of the meridian transit. The instrument had Tycho's famous tranversal system for accurate readings. It could be read to a sixth of a minute, that is ten seconds. Tycho also called the instrument the Tychonian quadrant. The wall behind the instrument was beautifully decorated by famous artists.
The revolving azimuth quadrant (1586)

This instrument was made partly of steel, partly of brass. The radius was 155 cm. It had an azimuth circle, 230 cm in diameter, mounted directly on the wall. Both altitudes and azimuths could be taken. The instrument was placed in the northeastern crypt of Stjerneborg. It had a scale with the minutes divided into four parts, which allowed readings to an accuracy of fifteen seconds. The instrument was turnable all around the horizon. With this instrument, Tycho very carefully (by means of Polaris) determined the latitude of his observatory. He measured the highest and lowest altitude of the star. From several observations he calculated a mean figure. His latitude differs from the correct one by only fourteen seconds! In the same way, Tycho measured the star in its most easterly and westerly positions and determined the direction of the meridian, the true north direction. The error was less than half a minute.
The great steel quadrant (1588)

With the great mural quadrant, it was possible to measure altitudes only in the meridian. This was not satisfactory. Tycho, therefore, also construc-ted quadrants turnable in the horizontal plane, that made it possible not only to take sights in all directions, but also to determine the direction; the azimuth. The previously described instrument was one of these, and this one is another. This one was the biggest of Tychos quadrants, 194 cm in radius. The azimuth circle on the wall was 350 cm in diameter. The instrument was built of steel but the scale and the sights were of brass. It could be read to an accuracy of ten seconds. The quadrant was circumscribed by a quadrangle in steel which gave a superb stability to the instrument. Tycho said a person could climb on to the instrument and, hanging on to it, be turned around without the instrument being damaged. The instrument was placed in the southwestern crypt of Stjerneborg. The stone steps and the stone pillar in the middle of the crypt still remain and can be seen in the ruins of Stjerneborg.
The great azimuth semicircle (1588)

In the larger southern observatory of Uraniborg, there also stood the great azimuth semicircle; an instrument designed to measure azimuths as well as altitudes. It was made of steel covered with brass. The semicircle was 233 cm in diameter. The diameter of the horizontal circle below it was 155 cm. A ruler furnished with a sight was turnable around a point at the end of the semicircle's diameter. The altitude could be read on a scale on the semicircle, and the azimuth on the horizontal ring. On the top of the instrument, three goddesses sat on thrones. Highest was Urania representing Astronomy, the queen of sciences. Below her in women's shape, on the one side was Geometry with triangles in her hands, on the other side was Arithmetic with figures in her hands. This instrument could easily be disassembled and remounted in another place, too.
The parallactic instrument

This instrument was also called a triquetrum or Ptolemean rulers. It is said to be made mostly of brass. The lengths of the rulers were 155 cm. The instrument was placed in the larger southern observatory of Uraniborg. The instrument was used to determine zenith distances, especially to calculate parallaxes. The zenith distance of a heavenly body is 90° minus its altitude. The instrument could be turned in the horizontal plane into different azimuths, but the azimuth could not be read. Most of Tycho's instruments had to be adjusted before use. This was often done by means of plumbs. On this instrument, the plumb was hidden in a casing to avoid disturbances by the wind.

Tycho also owned a similar instrument once belonging to Nicolaus Copernicus. Tycho had received it as a gift. It was made of wood. The scale was drawn with ink. Tycho highly valued the instrument but he considered it antique and did not use it.
The parallactic instrument with an azimuth circle (1583)

This instrument was the biggest Tycho constructed and built on the island of Ven. It had a fixed place in the largest northern observatory of Uraniborg. It is said to be made of solid brass. The rulers together had a length of 330 cm. The azimuth circle was placed on the wall's edge. It had a diameter of 466 cm. The rulers were held together with a hinge and were hoisted by means of a rope passing over a little wheel at the instruments' top. The instrument was read at a plumb line on a scale on the horizontal balk. Zenith distances and azimuths, especially the latter, could be determined very accurately. Tycho started in 1581 to regularly observe the moon with this type of instrument. Over a period of fifteen years he collected more than 400 observations of the moon in his journals. He discovered the inclination of the lunar orbit referred to the ecliptic to be irregular. He also found the intersections between the lunar orbit and the ecliptic to be moving slightly and irregularly to the west.
The zodiacal armillary sphere (1581)

Tycho had several armillary spheres. They were of two kinds, known as zodiacal or equatorial armillas, depending on which coordinate system they referred to. In the zodiacal system, the coordinates are celestial longitude and latitude (not to be confused with longitude and latitude on the earth). Longitude is measured from the first point of Aries along the ecliptic in an easterly direction. Latitude is the perpendicular distance from the ecliptic. When an observation was to be taken, the sphere first had to be orientated against true north and the elevation of the pole (the observer's latitude) had to be set. The innermost ring representing the ecliptic, had to be set in the right position momentarily because of the earth's daily rotation. This could be done against a star with a known longitude. Tycho complained of the weight of the rings. They were too heavy which affected the accuracy. The outermost ring had a diameter of 117 cm. The instrument was placed in the northwestern crypt of Stjerneborg.
The north equatorial armillary sphere (1584)

The two small observatories in the castle each gave room to only one instrument. There were two equatorial armillary spheres, of the same size, but somewhat different in construction. The dia-meter of the outermost ring was 155 cm. This instrument was placed in the smaller northern observatory of Uraniborg. The outer ring was made of steel but the inner rings were of brass. In the equatorial system the coordinates are right ascension and declination. Right ascension is measured along the equator from the first point of Aries to the east. Declination is the perpendicular distance from the equator. Before observations were taken, the instrument had to be adjusted in the northerly direction and the elevation of the pole above the horizon (the observer's latitude) had to be set. It was used in the same way as the next instrument. The instrument carried the portraits of four well-known astronomers, Ptolemy, Al Battini, Copernicus and Tycho himself.
The south equatorial armillary sphere (1584)

This sphere was functionally similar to the previous one. Its was placed in the smaller southern observatory of Uraniborg. The reason Tycho had two similar armillas, one in each end of the castle, was that the towers of the castle were a hindrance to making observations in some directions. Tycho also often made simultaneous observations with different instruments and different observers. This instrument had three movable rings of steel. The outer ring had no other function than to make the instrument more stable. After adjustments were made (see previous instrument) observations could be taken by the sights on the rings and the little cylinder in the centre of the instrument. The declination could be read directly on its ring. As the first point of Aries is not to be seen on the sky, the right ascension could not be read as easily. However, the differences in right ascension between stars with known right ascension and unknown stars could be taken, and the right ascension of the unknown stars could be calculated.
The great equatorial armillary sphere (1585)

Tycho was a precursor with equatorial armillary spheres. This instrument was built later than the armillas of the castle and meant a great advance in construction. It was bigger and simpler to use. It consisted of one single declination circle, 272 cm in diameter, and a semicircle representing the equator, 350 cm in diameter. It was made of steel with scales and sights in brass. The instrument's axis was very carefully adjusted to be parallel with the axis of the earth, as well as the semicircle being accurately adjusted to the equatorial plane. Two rulers, turnable around the centre of the instrument, carried sights in their outer ends and were used to determine declination. Two more sights slid along the equator. Between those, the difference of right ascension between two heavenly bodies could be found. Also the hour angle could be read on the equator. The angles could be read to an accuracy of a quarter of a minute; that is fifteen seconds. The instrument was placed in the southern and largest crypt of Stjerneborg, under the observatory's big cupola.
The bipartite arc for small angles (1583)

Tycho designed several instruments to use for measuring small angles. This instrument is one of those. It consisted of two arcs of brass, each covering 30°. They were mounted on the end of a 155 cm long bar of iron with two small cylinders as aiming points in the opposite end. The instrument was handled by two observers. It was used to measure interstellar distances up to 30°. The instrument was hung on a pillar and was possible to move in all directions and put into any plane. With this instrument Tycho later checked all the distances between the stars in the constellation of Cassiopeia, those he determined together with the Stella Nova in 1572. He found no reason to change his mind about the new star. The distances to the star itself he could not check. The star had now faded away and could not be seen with the naked eye any longer. This instrument was placed in the larger northern observatory of Uraniborg.
The triangular astronomical sextant

This sextant was probably Tycho's best. The radius was 155 cm. It was to a great part made of wood. Tycho did not often use this material but the advantage of wood was the lighter weight. When Tycho used wood he chose well-selected pieces of walnut or pine. He covered it with canvas and coated it with a mixture of white lead and linseed oil, all to prevent the wood from changing form. The limb and the sights were as usual made of brass. The instrument was mounted on a globe, made of copper, with a diameter of 52 cm. This made it possible to turn the instrument in all directions and put it in every plane. It took two observers to use it. If the angle to be measured was very small the two observers came very close together. In that case an extra sight was used. The instrument was primarily used to determine distances between stars with, but was also used to measure altitudes, especially planets' altitudes. The planets never exceeded 60° in altitude at Tycho's latitude. This instrument could be read to a quarter of a minute and was erected in the southeastern crypt of Stjerneborg.
The sextant of steel for one observer (1574)

This was one of Tycho's early instruments. It was made of steel with the scale and sights of brass. It was specially designed for use by one single observer. It could be turned and adjusted into any plane and was used primarily for measuring interstellar distances. Its was placed in the larger northern observatory of Uraniborg. Tycho considered it sometimes an advantage to be able to make the observation by only one observer. However, the observations were taken with more trouble and the results were not as good as with the bigger sextants. This instrument could also be taken to pieces and remounted in another place. Tycho took observations on the comet of 1577 with the instrument. The landgraf Wilhelm of Hesse who had an observatory in Cassel, copied the instrument.
Another instrument for small angles (1572)

This is an early instrument to be used by one single observer. It was probably constructed at Herrevadskloster and used for observations of the new star. It could be used to determine star distances up to 30°. Tycho says the limb with the scale could be changed to a longer one covering 60°, as is shown on the next picture. It is uncertain if the pictures show two different instruments or if it is the same instrument with two different limbs. The limb was made of copper. The radius was 155 cm. The two sides were movable and held together by a hinge. The adjustment to right angle was done by a screw. The instrument had no fixed arrangement of mounting for observations but was held in the hands. It was kept in the larger northern observatory. Tycho considered the instrument somewhat antique. He refers to it as an example of a simple and cheap instrument for those who cannot afford to build better.
The sextant of Herrevadskloster (1572)

In 1572, when Tycho was staying with his uncle at Herrevadskloster, he built a new sextant. Thanks to this, he possessed a rather good one when the new star showed up in the sky. The instrument consisted of two legs made of walnut wood, 32 x 48 mm with a length of 155 cm, and covered with copperplating. The legs were linked together by a hinge. One leg was considered as fixed, while the other was adjustable by a screw. The limb and the sights were made of copper. Tycho very carefully measured the distances between the new star and the principal eight stars of Cassiopeia. The star was circumpolar and the upper meridian transit was close to zenith. Tycho could not determine that altitude with this instrument. However, he measured the altitude of the transit of the lower meridian. To do this, he placed the instrument in a window as shown on the picture. The instrument was kept in the larger northern observatory. Tycho already considered it antique. See also previous instrument.
The quadrant of Augsburg (1570)

This very big quadrant was constructed by Tycho and built in Augsburg in 1570. It was erected in a park on the manor of the alderman, Paul Hainzel, outside the town. The radius was no less than 543 cm. Tycho never constructed such a big instrument later. It was built of oak and strengthened with iron. The arc was plated with brass and parted into 90 degrees. Every degree was parted into 60 minutes. A minute of arc of this quadrant had a length of 1.6 mm. The instrument was hung on a vertical pillar made of oak. The quadrant could be turned around the centre of the circle and locked. The pillar was first turned and the instrument adjusted to the object's vertical plane by levers. The reading was made at a plumb line. It took forty strong men to erect the instrument on a little hill in the park. The instrument was, because of its weight, very inconvenient to use. When Tycho again visited Augsburg in 1575 he found the instrument in ruins. It had blown down during a storm and not been repaired again.
The great steel quadrant (1581)

This instrument is the same as one shown before called "The great steel quadrant". It was originally built in 1581 but was somewhat modified in 1588 and moved to Stjerneborg, where it was erected upside down in the southwestern crypt. It was first mounted on an azimuth horizon (probably of iron) which was placed on five stone columns. The quadrant had a considerable weight and could only be turned with difficulty on the azimuth horizon. The transferring was an improvement. Its first location was probably the larger southern observatory of the castle. When it was moved, the stone columns could have been used for the great semicircle built in the same year.
The great brass globe (1584)

The year 1584 is engraved on the globe, however, it was then still not completed. Tycho ordered it from a craftsman in Augsburg in 1570. The interior was made of selected wood. When Tycho visited Augsburg five years later, he found the globe cracked. He had it repaired and, not without trouble, sent home to Denmark. At Ven, he carefully mended it again and adjusted its spherical shape very thoroughly by applying several sheets of parchment to it. Then he let it stand for two whole years to see if it could stand the changes of temperature without changing its shape. After that he covered the entire globe with a plating of brass. This was done so cleverly that it was hardly possible to see the joining of the plates. He waited another year, then he had the equator and the ecliptic engraved on it. After that priority came the principal constellations. On the declination circle, or meridian, the pole's elevation above the horizon could be set and the declinations could be read. On the broad horizon circle, the azimuth was read. There was also a vertical circle with a scale for reading altitudes. All the scales had Tycho's transversal system and were possible to read to a minute of an arc. This circle also had an inscription in Latin which ended, "thus by a mechanical piece of work opening the sky to those of the inhabitants of the earth who are able to comprehend this system of reason." During many years Tycho worked to fill the globe with star positions. The number finally exceeded one thousand which had been the big goal. The diameter of the globe was about 150 cm. Its location was the library of the castle. When the globe was not used, it was protected by a heaven made of silk that could be hoisted up. It must have been quite an imposing sight; in total nearly three metres in height.
Ground of the Uraniborg (about 1590)

The castle and its ground were perfectly orientated in the points of the compass. The surrounding walls of about 5 metres high formed a square with sides of 77.7 metres. In every corner there was a building. To the east and to the west there were the gatehouses with watching dogs on the upper floor. In the south corner there was a house for book printing and in the north corner a house for the servants. In the middle of each wall there were bastions with small summerhouses. The garden held more than 300 fruit trees. There were also gardens for flowers and spices. The whole establishment was very symmetrically built. In the middle stood Urania's castle, built of red brick with its towers and copulas on top of the observatories. The architecture was Dutch renaissance. There were stone works of grey limestone and marble around the windows and the entrances. On the top there was a Pegasus figure showing the wind direction, not only to those outside the castle but, by one of Tycho's many automations, also inside the castle.
The castle of Uraniborg (1580)

The castle was rather small, about 15 metres square, with circular annexes in the north and south. The castle had a cellar, two living floors and a loft floor. The cellar had, in the north, room for food and stores of different kinds. In the south end, Tycho had sixteen furnaces for his alchemical experiments. On the first floor, the kitchen was in the north end and the library in the south. There were four square-shaped rooms for daily living for work and guests. On the second floor, there was one large room facing to the west with a marvellous view of the Sound, called the summer room. To the east, there were two smaller rooms called the king's and the queen's chambers. In extensions to the north and to the south, there were at each end a bigger and a smaller circular observatory with copulas, which could be opened in all directions. Around the observatories, there were balconies with stands where smaller instruments could be mounted. In the loft floor, there were eight smaller chambers for Tycho's assistants. The castle was abundantly decorated with sculptural works, paintings, etc. associating with what the castle was dedicated to; astronomy.
The observatory of Stjerneborg (1586)

Tycho soon wanted to build a second generation's instruments, bigger and more accurate. He had also experienced disadvantages with the observatories in the castle. They were not stable enough and the instruments were sometimes exposed to disturbances by wind and weather. Therefore he built a new observatory, "seventy small double steps", south of the castle. He named it Stjerneborg. It consisted of five circular crypts, dug out and constructed under ground level and with roofs that could be opened up or taken away. Between the crypts there was a little square study with sides of about 2.5 metres. There was an oven for heating, a table for making calculations at and places for some small instruments to hang on the walls. In the east wall, there was a bed for Tycho and, between the southwestern crypt and the study, there was a small alcove for the assistants to rest in if the weather turned cloudy. In each crypt a major instrument was erected. The entrance to the observatory was from the north. Also in this observatory, there were several sculptures and paintings. The upper illustration is seen from the west. On the one below, north is downwards. On the ground, the observatory was surrounded by a fence in the shape of a quadrangle. The sides were 18 metres. There were several stands to support instruments.

The island of Ven

The name of the island can be seen spelled in many ways. Tycho spelled it Hveen, sometimes Hvenna; in Latin Venusia. The modern spelling in Swedish is Ven but the people living on the island still prefer to spell the name of their island, Hven. The island is situated in the Sound between Denmark and Sweden, some 25 kilometres north of Copenhagen and 7 kilometers northwest of Landskrona. The island was ceded to Sweden in 1660 and has belonged to this country ever since. In 1959 the island was incorporated in the municipality of Landskrona. The island is about 4.5 by 2.4 kilometres. It is a very fertile plateau of moraine clay, 20 to 40 metres high and with the shores rising steeply from the sea. There is scarcely any wood on the island. The castle Uraniborg was built in the middle of the island on its highest point, about 45 metres above the sea level. Tycho Brahe received the island as a grant from the King of Denmark in 1576. He lived and worked here until 1597, when he due to disagreements with the court in Copenhagen abandoned the island and became Astronomer to the Emperor in Prague. He died there in 1601. One of his assistants, Johannes Kepler, obtained access to Tycho's comprehensive journals of observations. From them he deduced the laws of planetary motion, known as Keplers' Laws.