A mural instrument is an

angle measuring instrument A measuring instrument is a device to measure a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Establis ...

mounted on or built into a wall. For astronomical purposes, these walls were oriented so they lie precisely on the

meridian Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...

. A mural instrument that measured angles from 0 to 90 degrees was called a mural quadrant. They were utilized as astronomical devices in ancient Egypt and

ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...

Edmond Halley Edmond (or Edmund) Halley (; – ) was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena in 1676–77, H ...

, due to the lack of an assistant and only one vertical wire in his

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1979 film), a 1979 Israeli film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world * ''Transit'' (2006 film), a 2006 ...

, confined himself to the use of a mural quadrant built by

George Graham George Graham (born 30 November 1944), nicknamed "Stroller", is a Scottish former Association football, football player and manager (association football), manager. In his successful playing career, he made 455 appearances in England's Football ...

after its erection in 1725 at the

Royal Observatory, Greenwich The Royal Observatory, Greenwich (ROG; known as the Old Royal Observatory from 1957 to 1998, when the working Royal Greenwich Observatory, RGO, temporarily moved south from Greenwich to Herstmonceux) is an observatory situated on a hill in ...

Bradley Bradley is an English surname derived from a place name meaning "broad wood" or "broad meadow" in Old English. Like many English surnames Bradley can also be used as a given name and as such has become popular. It is also an Anglicisation of t ...

's first observation with that quadrant was made on 15 June 1742. The mural quadrant has been called the "quintessential instrument" of 18th century (i.e. 1700s) observatories. It rose to prominence in the field of

positional astronomy Spherical astronomy, or positional astronomy, is a branch of observational astronomy used to locate astronomical objects on the celestial sphere, as seen at a particular date, time, and location on Earth. It relies on the mathematical methods of ...

at this time.

Construction

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

degree Degree may refer to: As a unit of measurement * Degree (angle), a unit of angle measurement ** Degree of geographical latitude ** Degree of geographical longitude * Degree symbol (°), a notation used in science, engineering, and mathematics ...

s 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 An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...

. The angle is then read, yielding the

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vert ...

or altitude of the object. In smaller instruments, an

alidade An alidade () (archaic forms include alhidade, alhidad, alidad) or a turning board is a device that allows one to sight a distant object and use the line of sight to perform a task. This task can be, for example, to triangulate a scale map on site ...

could be used. More modern mural instruments would use a

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...

with a

reticle A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscope, ...

eyepiece to observe the object. Many mural quadrants were constructed, giving the observer the ability to measure a 90° range of

. There were also mural sextants that read 60°. Mural quadrants of the 17th century were noted for their expense, with Flamsteed's costing 120 pounds (1689), and Edmund Halley's costing over 200 pounds (1725). 120 pounds of 1689 converted to the 2019 U.S. dollars can be estimated at over US$30,000, and 200 pounds of 1725 to over US$50,000. The large fixed quadrants were more expensive than a typical portable quadrant, with a Bird 2-foot quadrant costing 70 guineas.

Usage

In order to measure the position of, for example, a star, the observer needs a

sidereal clock Sidereal time (as a unit also sidereal day or sidereal rotation period) (sidereal ) is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coord ...

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

ing 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 In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...

. If the sidereal clock is precisely synchronized with the stars, the time yields the

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the earth. When paired w ...

directly.

Famous mural instruments

* A mural

sextant A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celes ...

was constructed in

Ray, Iran Shahr-e Ray ( fa, شهر ری, ) or simply Ray (Shar e Ray; ) is the capital of Ray County in Tehran Province, Iran. Formerly a distinct city, it has now been absorbed into the metropolitan area of Greater Tehran as the 20th district of municip ...

, by

Abu-Mahmud al-Khujandi Abu Mahmud Hamid ibn al-Khidr al-Khojandi (known as Abu Mahmood Khojandi, Alkhujandi or al-Khujandi, Persian: ابومحمود خجندی, c. 940 - 1000) was a Muslim Transoxanian astronomer and mathematician born in Khujand (now part of Tajikista ...

in 994. *

Ulugh Beg Mīrzā Muhammad Tāraghay bin Shāhrukh ( chg, میرزا محمد طارق بن شاہ رخ, fa, میرزا محمد تراغای بن شاہ رخ), better known as Ulugh Beg () (22 March 1394 – 27 October 1449), was a Timurid sultan, as ...

constructed the "Fakhri Sextant" in

Samarkand fa, سمرقند , native_name_lang = , settlement_type = City , image_skyline = , image_caption = Clockwise from the top:Registan square, Shah-i-Zinda necropolis, Bibi-Khanym Mosque, view inside Shah-i-Zinda, ...

that had a radius of 40 meters. 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 Tycho Brahe ( ; born Tyge Ottesen Brahe; generally called Tycho (14 December 154624 October 1601) was a Danish astronomer, known for his comprehensive astronomical observations, generally considered to be the most accurate of his time. He was k ...

's mural quadrant in

Uraniborg Uraniborg ( da, Uranienborg, sv, Uraniborg) was a Danish astronomical observatory and alchemy laboratory established and operated by Tycho Brahe. It was built on Hven, an island in the Øresund between Zealand and Scania, Sweden, which was ...

Hven Ven ( da, Hven, older Swedish spelling Hven) is a small Swedish island in the Øresund strait, between Scania and Zealand (Denmark). It is part of Landskrona Municipality, Scania County. The island has 371 inhabitants and an area of . During th ...

(now

Ven Ven may refer to: Places * Ven, Heeze-Leende, a hamlet in the Netherlands * Ven (Sweden), an island * Ven, Tajikistan, a town * VEN or Venezuela Other uses * von Economo neurons, also called ''spindle neurons'' * '' Vên'', an EP by Eluveiti ...

in Sweden). * The mural quadrant at the

, in east London. *

Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...

's mural quadrant at

Alexandria Alexandria ( or ; ar, ٱلْإِسْكَنْدَرِيَّةُ ; grc-gre, Αλεξάνδρεια, Alexándria) is the second largest city in Egypt, and the largest city on the Mediterranean coast. Founded in by Alexander the Great, Alexandria ...

. This instrument is also referred to as a ''plinth''. * The obsolete constellation

Quadrans Muralis Quadrans Muralis (Latin for ''mural quadrant'') was a former constellations, constellation created by the French astronomer Jérôme Lalande in 1795. It depicted a wall-mounted quadrant with which he and his nephew Michel Lefrançois de Lalande ha ...

represents a mural quadrant. * The mural quadrant at the

Mannheim Observatory The Mannheim Observatory was a tower observatory built between 1772 and 1774 in Mannheim, Germany, which remained in operation until 1880. The observatory was transferred to Karlsruhe and finally in 1898, was established on the Königstuhl near ...

in Germany.Mannheimer Observatory quadrant
/ref> This is another of John Bird's instruments.

References

External links

* {{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Ancient Greek astronomy Ancient Egyptian science Ancient Egyptian technology Astronomical instruments Historical scientific instruments Astronomy in the medieval Islamic world Technology in the medieval Islamic world Angle measuring instruments Egyptian inventions

Construction

Usage

Famous mural instruments

See also

References

External links