Mural instrument

Mural instrument
Tycho Brahe's mural quadrant
Mural quadrant constructed as a frame mounted on a wall. This instrument was made by John Bird in 1773 and is in the Museum of the History of Science, University of Oxford.

A mural instrument is an angle measuring device mounted on or built into a wall. For astronomical purposes, these walls were oriented so they lie precisely on a meridian. A mural instrument that measured angles from 0 to 90 degrees was called a mural quadrant.

Contents

Construction

A Bird Mural Quadrant was for many years the main instrument of the Mannheim Observatory, shown here installed

Many older mural quadrants have been constructed by marking directly on the wall surfaces. More recent instruments were made with a frame that was constructed with precision and mounted permanently on the wall.

The arc is marked with divisions, almost always in degrees and fractions of a degree. In the oldest instruments, an indicator is placed at the centre of the arc. An observer can move a device with a second indicator along the arc until the line of sight from the movable device's indicator through the indicator at the centre of the arc aligns with the astronomical object. The angle is then read, yielding the elevation or altitude of the object. In smaller instruments, an alidade could be used. More modern mural instruments would use a telescope with a reticle eyepiece to observe the object.

Many mural quadrants were constructed, giving the observer the ability to measure a full 90° range of elevation. There were also mural sextants that read 60°.

Usage

In order to measure the position of, for example, a star, the observer needs a sidereal clock in addition to the mural instrument. With the clock measuring time, a star of interest is observed with the instrument until it crosses an indicator showing that it is transiting the meridian. At this instant, the time on the clock is recorded as well as the angular elevation of the star. This yields the position in the coordinates of the instrument. If the instrument's arc is not marked relative to the celestial equator, then the elevation is corrected for the difference, resulting in the star's declination. If the sidereal clock is precisely synchronized with the stars, the time yields the right ascension directly[1].

Famous mural instruments

Ulugh Beg's mural sextant, constructed in Samarkand, Uzbekistan during the 15th century.
  • A mural sextant was constructed in Ray, Iran, by Abu-Mahmud al-Khujandi in 994.[2]
  • Ulugh Beg constructed the "Fakhri Sextant" that had a radius of 40 meters.[3] Seen in the image on the right, the arc was finely constructed with a staircase on either side to provide access for the assistants who performed the measurements.
  • Tycho Brahe's mural quadrant in Uraniborg at Hven.
  • The mural quadrant at the Greenwich Observatory.
  • Ptolemy's mural quadrant at Alexandria. This instrument is also referred to as a plinth.[4]
  • The obsolete constellation Quadrans Muralis represents a mural quadrant.
  • The mural quadrant at the Mannheimer Observatory.[5] This is another of John Bird's instruments.

References

  1. ^ Sidereal Time
  2. ^ O'Connor, John J.; Robertson, Edmund F., "Abu Mahmud Hamid ibn al-Khidr Al-Khujandi", MacTutor History of Mathematics archive, University of St Andrews, http://www-history.mcs.st-andrews.ac.uk/Biographies/Al-Khujandi.html .
  3. ^ Ulugh Beg, Dictionary of Scientific Biography.
  4. ^ Hoyle, Fred, Astronomy, A history of man's investigation of the universe, Crescent Books, Inc., London 1962, p 37.
  5. ^ Mannheimer Observatory quadrant



Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • mural — mural, ale (mu ral, ra l ) adj. 1°   De mur, qui a rapport aux murs. •   On a donné le nom de sel mural au natron qui se forme contre les vieux murs ; il est ordinairement mêlé d une grande quantité de substance calcaire, BUFF. Min. t. III, p.… …   Dictionnaire de la Langue Française d'Émile Littré

  • MURAL — ALE. adj. Il n est guère usité que dans les locutions suivantes :  Couronne murale, Couronne qu on donnait, chez les Romains, à ceux qui dans un assaut avaient monté les premiers sur les murs de la ville assiégée.  Cercle mural, Instrument… …   Dictionnaire de l'Academie Francaise, 7eme edition (1835)

  • mural circle — Circle Cir cle (s[ e]r k l), n. [OE. cercle, F. cercle, fr. L. circulus (Whence also AS. circul), dim. of circus circle, akin to Gr. kri kos, ki rkos, circle, ring. Cf. {Circus}, {Circum }.] [1913 Webster] 1. A plane figure, bounded by a single… …   The Collaborative International Dictionary of English

  • Quadrant (instrument) — Ptolemy using a quadrant A quadrant is an instrument that is used to measure angles up to 90°. It was originally proposed by Ptolemy as a better kind of astrolabe.[1] Several different variations of the instrument were later produced by medieval… …   Wikipedia

  • Quadrant (instrument) — Pour les articles homonymes, voir Quadrant. Le quadrant mobile d Augustin Stark (1815). Le quadrant est un ancien instrument de navigation qui servait à faire le point sur sa position en …   Wikipédia en Français

  • Transit instrument — In astronomy, transit instruments are used for the precise observation of star positions. The instruments can be divided into three groups: Meridian instruments for observation of star transits in the exact direction of South or North: * Meridian …   Wikipedia

  • William Simms (instrument maker) — Infobox Person name = William Simms image size = 165px caption = birth name = birth date = December 7 1793 birth place = Birmingham, England death date = June 21 1860 death place = Carshalton, Surrey, England residence = nationality = known for …   Wikipedia

  • Sextant (astronomical) — This article is about the Sextant as used for astrometry. For the navigator s sextant, see Sextant . Sextants for astronomical observations were used primarily for measuring the positions of stars. They are little used today, having been replaced …   Wikipedia

  • Inventions in medieval Islam — A significant number of inventions were developed in the medieval Islamic world, a geopolitical region that has at various times extended from Al Andalus and Africa in the west to the Indian subcontinent and Malay Archipelago in the east.… …   Wikipedia

  • List of inventors — This is a list of inventors. See also: List of scientists, Timeline of invention, List of inventions named after people, List of inventors killed by their own inventions, and . Alphabetical list compactTOC NOTOC A * Vitaly Mikhaylovich Abalakov,… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”