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Tycho Brahe
Accurate Astronomical Observations With Mechanical Instruments
(Naked Eye Astronomy)
Hands On Activity: Build and Use a Sextant or Quadrant

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  • Tycho Brahe's Astronomical Inventions and Contributions

    Tycho Ottesen Brahe
    Tycho Ottesen Brahe

    Tycho Brahe (1546 – 1601), was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations. One of his greatest achievements is the observation (naked eye) of the SN 1572 supernova on 11 November 1572 which had unexpectedly appeared in the constellation Cassiopeia. Brahe was well known in his lifetime as an astronomer, astrologist and alchemist.

    Tycho Brahe was granted, by the Danish king Fredrik II, an estate on the island of Hven and the funding to build the Uraniborg, an early research institute, where he built large astronomical instruments and took many careful measurements. After disagreements with the new king in 1597, he was invited by the Czech king and Holy Roman emperor Rudolph II to Prague, where he became the official imperial astronomer and he built a new observatory. Here, from 1600 until his death in 1601, he was assisted by Johannes Kepler. Kepler would later use Tycho's astronomical information to develop his own theories of astronomy.

    As an astronomer, Tycho worked to combine what he saw as the geometrical benefits of the Copernican system with the philosophical benefits of the Ptolemaic system into his own model of the universe, the Tychonic system.

    Tycho himself was not a Copernican, but proposed his Tychonic system in which the Sun orbited the Earth while the other planets orbited the Sun. His system provided a safe position for astronomers who were dissatisfied with older models but were reluctant to accept the Earth's motion. It gained a considerable following after 1616 when Rome decided officially that the heliocentric model was contrary to both philosophy and Scripture, and could be discussed only as a computational convenience that had no connection to fact.

    Tycho Brahe's Tychonic System
    In this depiction of the Tychonic system, the objects on blue orbits (the moon and the sun) revolve around the earth. The objects on orange orbits (Mercury, Venus, Mars, Jupiter, and Saturn) revolve around the sun. Around all is sphere of fixed stars.

    Tycho is credited with the most accurate astronomical observations of his time, and the data was used by his assistant Kepler to derive the laws of planetary motion. No one before Tycho had attempted to make so many redundant observations, and the mathematical tools to take advantage of them had not yet been developed. He did what others before him were unable or unwilling to do – to catalogue the planets and stars with enough accuracy to determine whether the Ptolemaic or Copernican system was more valid in describing the heavens.

    In 1559, Tycho began his studies at the University of Copenhagen. There he studied law but also studied a variety of other subjects and became interested in astronomy. It was, however, the eclipse which occurred on 21 August 1560, particularly the fact that it had been predicted, that so impressed him that he began to make his own studies of astronomy, helped by some of his professors. He purchased an ephemeris (a table of values that gives the positions of astronomical objects in the sky at a given time or times) and astronomy books.

    Tycho realized that progress in the science of astronomy could be achieved not by occasional haphazard observations, but only by systematic and rigorous observation, night after night, and by using instruments of the highest accuracy obtainable. He was able to improve and enlarge the existing instruments, and construct entirely new ones. Tycho's naked eye measurements of planetary parallax were unprecedented in their precision - accurate to the arcminute, or 1/30 the width of the full moon. His sister Sophia assisted Tycho in many of his measurements. These jealously guarded measurements were "usurped" by Kepler following Tycho's death. Tycho was the last major astronomer to work without the aid of a telescope, soon to be turned skyward by Galileo.

    Although, Tycho's planetary model became discredited, his astronomical observations are considered an essential contribution to the Scientific Revolution. Tycho was primarily an empiricist, who set new standards for precise and objective measurements.

    Tycho considered astrology a subject of great importance, and he was in his own time also famous for his contributions to medicine and his herbal medicines were in use as late as the 1900s.

    While a student, Tycho lost part of his nose in a duel. This occurred in the Christmas season of 1566, after a fair amount of drinking, while Tycho, just turned 20 years old, was studying at the University of Rostock in Germany. Attending a dance at a professor's house, he quarreled with a fellow Danish nobleman. The subsequent duel resulted in Tycho losing the bridge of his nose. From this event Tycho became interested in medicine and alchemy. For the rest of his life, he was said to have worn a false nose made of silver and gold, using a paste to keep it attached.

    Tycho died on 24 October 1601 in Prague, eleven days after suddenly becoming very ill during a banquet. For hundreds of years, the general belief was that he had developed a bladder infection which later killed him. This theory was supported by Kepler's first-hand account.

    Recent investigations have suggested that Tycho did not die from urinary problems but instead from mercury poisoning: extremely toxic levels of it have been found in his hair and hair-roots which had been stored in Prague.

    Tycho could have poisoned himself since he was an alchemist toying with mercury compounds among others.

    Build Your Own Sextant or Quadrant

    As stated above, Tycho Brahe's contributions to astronomy were enormous. He not only designed and built instruments, he also calibrated them and checked their accuracy periodically. He thus revolutionized astronomical instrumentation. He also changed observational practice profoundly. Whereas earlier astronomers had been content to observe the positions of planets and the Moon at certain important points of their orbits (e.g., opposition, quadrature, station), Tycho and his cast of assistants observed these bodies throughout their orbits.

    As a matter of fact Tycho Brahe, basically, used mainly a compass and a sextant or quadrant to observe the stars.

    Tycho Brahe's sextant
    Tycho Brahe's sextant, used for measuring the angular distances between stars.

    A compass is a navigational instrument for determining direction relative to the earth's magnetic poles. It consists of a magnetized pointer (usually marked on the North end) free to align itself with Earth's magnetic field. The face of the compass generally highlights the cardinal points of north, south, east and west. The compass greatly improved the safety and efficiency of travel, especially ocean travel. A compass can be used to calculate heading, used with a sextant to calculate latitude, and with a marine chronometer to calculate longitude. It thus provides a much improved navigational capability that has only been partially supplanted by modern devices such as the gyrocompass and the Global Positioning System (GPS).

    A sextant is an instrument generally used to measure the altitude of a celestial object above the horizon. Making this measurement is known as "sighting the object", "shooting the object", or "taking a sight". The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. A common use of the sextant is to sight the sun at noon to find one's latitude.

    Sextants for astronomical observations were used primarily for measuring the positions of stars. They are little used today, having been replaced over time by transit telescopes, astrometry techniques, and satellites such as Hipparcos.

    There are two types of astronomical sextants, mural instruments and frame-based instruments.

    Mural sextants are a special case of a mural instrument. Many were made that were quadrants rather than sextants. They were a kind of speciality of medieval Muslim astronomers to whom the credit of building the first mural sextants is attributed.

    Sextants and quadrants are very similar instruments. The difference between them is that a sextant is basically a sixty-degree (hence its name) arc aligned along a meridian (north-south line) and can measure angles up to 60 degrees, while a quadrant is a ninety degrees arc.

    For science fair projects and science hobbyists we suggest the following activity:

    • Build your own sextant or quadrant, draw your own star chart (many objects, or only a few), and compare its accuracy to commercial sextants or quadrants or to modern astronomical observations and maps.

    Before you begin, it's strongly recommended to consult professionals in the fields of astronomy and machinery, and of course not to ignore safety procedures.

    A few useful links to begin with:

    Build and Use Your Own Sextant / Quadrant
    Build a SimpleSextant
    Build a SimpleSextant
    Finding Your Latitude from the North Star by Building a Sextant
    The CD-Sextant
    The X-tant project
    Sextant Background, Construction and Usage
    How to Use a Sextant
    How a Sextant Works
    How to Build a Paper Quadrant

    Virtual Sky Maps
    Monthly sky maps for every location on Earth
    SFA Star Charts
    Using of a Star Chart
    An online star chart
    The Mag-7 Star Atlas Project
    Your Sky
    Historical Celestial Atlases on the World Wide Web

    Tycho Brahe Books


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    Last updated: June 2013
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