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 the meridian. 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. Edmond Halley, due to the lack of an assistant and only one vertical wire in his transit, confined himself to the use of a mural quadrant built by George Graham after its erection in 1725 at the Royal Observatory, Greenwich. Bradley'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 at this time.
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 90° range of elevation. 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.
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.
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 celestial navigation.
Mīrzā Muhammad Tāraghay bin Shāhrukh, better known as Ulugh Beg, was a Timurid sultan, as well as an astronomer and mathematician.
Sidereal time 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 coordinates in the night sky. Briefly, sidereal time is a "time scale that is based on Earth's rate of rotation measured relative to the fixed stars".
In astronomy and celestial navigation, the hour angle is one of the coordinates used in the equatorial coordinate system to give the direction of a point on the celestial sphere. The hour angle of a point is the angle between two planes: one containing Earth's axis and the zenith, and the other containing Earth's axis and the given point.
Timeline of telescopes, observatories, and observing technology.
Uraniborg was a Danish astronomical observatory and alchemy laboratory established and operated by Tycho Brahe. It was built c. 1576 – c. 1580 on Hven, an island in the Øresund between Zealand and Scania, Sweden, which was part of Denmark at the time. It was expanded with the underground facility Stjerneborg on an adjacent site.
The torquetum or turquet is a medieval astronomical instrument designed to take and convert measurements made in three sets of coordinates: Horizon, equatorial, and ecliptic. It is said to be a combination of Ptolemy's astrolabon and the plane astrolabe. In a sense, the torquetum is an analog computer.
The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the Sun or Moon. When observing the Sun, users kept the Sun to their back and observed the shadow cast by the upper vane on a horizon vane. It was invented by the English navigator John Davis, who described it in his book Seaman's Secrets in 1594.
Taqi ad-Din Muhammad ibn Ma'ruf ash-Shami al-Asadi was an Ottoman polymath active in Cairo and Istanbul. He was the author of more than ninety books on a wide variety of subjects, including astronomy, clocks, engineering, mathematics, mechanics, optics and natural philosophy.
The Constantinople observatory of Taqi ad-Din, founded in Constantinople by Taqi ad-Din Muhammad ibn Ma'ruf in 1577, was one of the largest astronomical observatories in medieval world. However, it only existed for a few years and was destroyed in 1580.
Abu Mahmud Hamid ibn Khidr Khojandi was a Muslim Central Asian astronomer and mathematician who lived in the late 10th century and helped build an observatory, near the city of Ray, in Iran. He was born in Khujand; a bronze bust of the astronomer is present in a park in modern-day Khujand, now part of Tajikistan.
The octant, also called reflecting quadrant, is a measuring instrument used primarily in navigation. It is a type of reflecting instrument.
The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir. These are special purpose telescopes mounted so as to allow pointing only in the meridian, the great circle through the north point of the horizon, the north celestial pole, the zenith, the south point of the horizon, the south celestial pole, and the nadir. Meridian telescopes rely on the rotation of the sky to bring objects into their field of view and are mounted on a fixed, horizontal, east–west axis.
Sextants for astronomical observations were devices depicting a sixth of a circle, used primarily for measuring the positions of stars. They are of significant historical importance, but have been replaced over time by transit telescopes, astrometry techniques, and satellites such as Hipparcos.
A quadrant is an instrument that is used to measure angles up to 90°. Different versions of this instrument could be used to calculate various readings, such as longitude, latitude, and time of day. It was originally proposed by Ptolemy as a better kind of astrolabe. Several different variations of the instrument were later produced by medieval Muslim astronomers.
Reflecting instruments are those that use mirrors to enhance their ability to make measurements. In particular, the use of mirrors permits one to observe two objects simultaneously while measuring the angular distance between the objects. While reflecting instruments are used in many professions, they are primarily associated with celestial navigation as the need to solve navigation problems, in particular the problem of the longitude, was the primary motivation in their development.
The sine quadrant was a type of quadrant used by medieval Arabic astronomers. It is also known as a "sinecal quadrant" in the English-speaking world. The instrument could be used to measure celestial angles, to tell time, to find directions, or to determine the apparent positions of any celestial object for any time. The name is derived from the Arabic "rub‘‘‘" meaning a quarter and "mujayyab" meaning marked with sine. It was described, according to King, by Muhammad ibn Mūsā al-Khwārizmī in 9th century Baghdad.
The Ulugh Beg Observatory is an observatory in Samarkand, Uzbekistan. Built in the 1420s by the Timurid astronomer Ulugh Beg, it is considered by scholars to have been one of the finest observatories in the Islamic world. Islamic astronomers who worked at the observatory include Al-Kashi, Ali Qushji, and Ulugh Beg himself. The observatory was destroyed in 1449 and rediscovered in 1908.
Jonathan Sisson was a prominent English instrument maker, the inventor of the modern theodolite with a sighting telescope for surveying, and a leading maker of astronomical instruments.