An astrolabe (Greek: ἀστρολάβος astrolabos; Arabic: ٱلأَسْطُرلاب al-Asturlāb; Persian: اِستاره یاب Astaara yab) is an elaborate inclinometer, historically used by astronomers and navigators to measure the altitude above the horizon of a celestial body, day or night. It can be used to identify stars or planets, to determine local latitude given local time (and vice versa), to survey, or to triangulate. It was used in classical antiquity, the Islamic Golden Age, the European Middle Ages and the Age of Discovery for all these purposes.
The astrolabe's importance not only comes from the early development of astronomy, but is also effective for determining latitude on land or calm seas. Although it is less reliable on the heaving deck of a ship in rough seas, the mariner's astrolabe was developed to solve that problem.
OED gives the translation "star-taker" for the English word astrolabe and traces it through medieval Latin to the Greek word astrolabos, from astron "star" and lambanein "to take". In the medieval Islamic world the Arabic word "al-Asturlāb" (i.e. astrolabe) was given various etymologies. In Arabic texts, the word is translated as "ākhdhu al-Nujuum" (Arabic: آخِذُ ٱلنُّجُومْ, lit. "star-taker"), a direct translation of the Greek word.
Al-Biruni quotes and criticizes medieval scientist Hamzah al-Isfahani who stated: "asturlab is an arabization of this Persian phrase" (sitara yab, meaning "taker of the stars"). In medieval Islamic sources, there is also a folk etymology of the word as "lines of lab", where "Lab" refers to a certain son of Idris (Enoch). This etymology is mentioned by a 10th-century scientist named al-Qummi but rejected by al-Khwarizmi.
An early astrolabe was invented in the Hellenistic civilization by Apollonius of Perga between 220 and 150 BC, often attributed to Hipparchus. The astrolabe was a marriage of the planisphere and dioptra, effectively an analog calculator capable of working out several different kinds of problems in astronomy. Theon of Alexandria (c. 335 – c. 405) wrote a detailed treatise on the astrolabe, and Lewis argues that Ptolemy used an astrolabe to make the astronomical observations recorded in the Tetrabiblos. The invention of the plane astrolabe is sometimes wrongly attributed to Theon's daughter Hypatia (c. 350–370; died 415 AD), but it is, in fact, known to have already been in use at least 500 years before Hypatia was born. The misattribution comes from a misinterpretation of a statement in a letter written by Hypatia's pupil Synesius (c. 373 – c. 414), which mentions that Hypatia had taught him how to construct a plane astrolabe, but does not state anything about her having invented it herself.
Astrolabes continued in use in the Greek-speaking world throughout the Byzantine period. About 550 AD, Christian philosopher John Philoponus wrote a treatise on the astrolabe in Greek, which is the earliest extant treatise on the instrument.[a] Mesopotamian bishop Severus Sebokht also wrote a treatise on the astrolabe in the Syriac language in the mid-7th century.[b] Sebokht refers to the astrolabe as being made of brass in the introduction of his treatise, indicating that metal astrolabes were known in the Christian East well before they were developed in the Islamic world or in the Latin West.
Astrolabes were further developed in the medieval Islamic world, where Muslim astronomers introduced angular scales to the design, adding circles indicating azimuths on the horizon. It was widely used throughout the Muslim world, chiefly as an aid to navigation and as a way of finding the Qibla, the direction of Mecca. Eighth-century mathematician Muhammad al-Fazari is the first person credited with building the astrolabe in the Islamic world.
The mathematical background was established by Muslim astronomer Albatenius in his treatise Kitab az-Zij (c. 920 AD), which was translated into Latin by Plato Tiburtinus (De Motu Stellarum). The earliest surviving astrolabe is dated AH 315 (927–28 AD). In the Islamic world, astrolabes were used to find the times of sunrise and the rising of fixed stars, to help schedule morning prayers (salat). In the 10th century, al-Sufi first described over 1,000 different uses of an astrolabe, in areas as diverse as astronomy, astrology, navigation, surveying, timekeeping, prayer, Salat, Qibla, etc.
The spherical astrolabe was a variation of both the astrolabe and the armillary sphere, invented during the Middle Ages by astronomers and inventors in the Islamic world.[c] The earliest description of the spherical astrolabe dates back to Al-Nayrizi (fl. 892–902). In the 12th century, Sharaf al-Dīn al-Tūsī invented the linear astrolabe, sometimes called the "staff of al-Tusi", which was "a simple wooden rod with graduated markings but without sights. It was furnished with a plumb line and a double chord for making angular measurements and bore a perforated pointer". The geared mechanical astrolabe was invented by Abi Bakr of Isfahan in 1235.
Herman Contractus, the abbot of Reichman Abbey, examined the use of the astrolabe in Mensura Astrolai during the 11th century. Peter of Maricourt wrote a treatise on the construction and use of a universal astrolabe in the last half of the 13th century entitled Nova compositio astrolabii particularis. Universal astrolabes can be found at the History of Science Museum in Oxford.
English author Geoffrey Chaucer (c. 1343–1400) compiled A Treatise on the Astrolabe for his son, mainly based on a work by Messahalla or Ibn al-Saffar. The same source was translated by French astronomer and astrologer Pélerin de Prusse and others. The first printed book on the astrolabe was Composition and Use of Astrolabe by Christian of Prachatice, also using Messahalla, but relatively original.
A simplified astrolabe, known as a balesilha, was used by sailors to get an accurate reading of latitude while out to sea. The use of the balesilha was promoted by Prince Henry (1394–1460) while out navigating for Portugal.
The first known metal astrolabe in Western Europe is the Destombes astrolabe made from brass in tenth-century Spain. Metal astrolabes avoided the warping that large wooden ones were prone to, allowing the construction of larger and therefore more accurate instruments. Metal astrolabes were heavier than wooden instruments of the same size, making it difficult to use them in navigation.
The astrolabe was almost certainly first brought north of the Pyrenees by Gerbert of Aurillac (future Pope Sylvester II), where it was integrated into the quadrivium at the school in Reims, France sometime before the turn of the 11th century. In the 15th century, French instrument maker Jean Fusoris (c. 1365–1436) also started remaking and selling astrolabes in his shop in Paris, along with portable sundials and other popular scientific devices of the day. Thirteen of his astrolabes survive to this day. One more special example of craftsmanship in early 15th-century Europe is the astrolabe designed by Antonius de Pacento and made by Dominicus de Lanzano, dated 1420.
In the 16th century, Johannes Stöffler published Elucidatio fabricae ususque astrolabii, a manual of the construction and use of the astrolabe. Four identical 16th-century astrolabes made by Georg Hartmann provide some of the earliest evidence for batch production by division of labor.
Mechanical astronomical clocks were initially influenced by the astrolabe; they could be seen in many ways as clockwork astrolabes designed to produce a continual display of the current position of the sun, stars, and planets. For example, Richard of Wallingford's clock (c. 1330) consisted essentially of a star map rotating behind a fixed rete, similar to that of an astrolabe.
Many astronomical clocks use an astrolabe-style display, such as the famous clock at Prague, adopting a stereographic projection (see below) of the ecliptic plane. In recent times, astrolabe watches have become popular. For example, Swiss watchmaker Dr. Ludwig Oechslin designed and built an astrolabe wristwatch in conjunction with Ulysse Nardin in 1985. Dutch watchmaker Christaan van der Klauuw also manufactures astrolabe watches today.
An astrolabe consists of a disk, called the mater (mother), which is deep enough to hold one or more flat plates called tympans, or climates. A tympan is made for a specific latitude and is engraved with a stereographic projection of circles denoting azimuth and altitude and representing the portion of the celestial sphere above the local horizon. The rim of the mater is typically graduated into hours of time, degrees of arc, or both.
Above the mater and tympan, the rete, a framework bearing a projection of the ecliptic plane and several pointers indicating the positions of the brightest stars, is free to rotate. These pointers are often just simple points, but depending on the skill of the craftsman can be very elaborate and artistic. There are examples of astrolabes with artistic pointers in the shape of balls, stars, snakes, hands, dogs' heads, and leaves, among others. The names of the indicated stars were often engraved on the pointers in Arabic or Latin. Some astrolabes have a narrow rule or label which rotates over the rete, and may be marked with a scale of declinations.
The rete, representing the sky, functions as a star chart. When it is rotated, the stars and the ecliptic move over the projection of the coordinates on the tympan. One complete rotation corresponds to the passage of a day. The astrolabe is, therefore, a predecessor of the modern planisphere.
On the back of the mater, there is often engraved a number of scales that are useful in the astrolabe's various applications. These vary from designer to designer, but might include curves for time conversions, a calendar for converting the day of the month to the sun's position on the ecliptic, trigonometric scales, and graduation of 360 degrees around the back edge. The alidade is attached to the back face. An alidade can be seen in the lower right illustration of the Persian astrolabe above. When the astrolabe is held vertically, the alidade can be rotated and the sun or a star sighted along its length, so that its altitude in degrees can be read ("taken") from the graduated edge of the astrolabe; hence the word's Greek roots: "astron" (ἄστρον) = star + "lab-" (λαβ-) = to take.
There is no evidence for the Hellenistic origin of the spherical astrolabe, but rather evidence so far available suggests that it may have been an early but distinctly Islamic development with no Greek antecedents.
Paul Kunitzsch has recently established that the Latin treatise on the astrolabe long ascribed to Ma'sh'allah and translated by John of Seville is in fact by Ibn al-Saffar, a disciple of Maslama al-Majriti.
A Treatise on the Astrolabe is a medieval instruction manual on the astrolabe by Geoffrey Chaucer. It describes both the form and the proper use of the instrument, and stands out as a prose technical work from a writer better known for poetry, written in English rather than the more typical Latin.Armillary sphere
An armillary sphere (variations are known as spherical astrolabe, armilla, or armil) is a model of objects in the sky (on the celestial sphere), consisting of a spherical framework of rings, centred on Earth or the Sun, that represent lines of celestial longitude and latitude and other astronomically important features, such as the ecliptic. As such, it differs from a celestial globe, which is a smooth sphere whose principal purpose is to map the constellations. It was invented separately in ancient Greece and ancient China, with later use in the Islamic world and Medieval Europe.
With the Earth as center, an armillary sphere is known as Ptolemaic. With the Sun as center, it is known as Copernican.The flag of Portugal features an armillary sphere. The armillary sphere is also featured in Portuguese heraldry, associated with the Portuguese discoveries during the Age of Exploration. In the flag of Empire of Brazil, the armillary sphere is also featured.Astrolabe Glacier
Astrolabe Glacier is a glacier 7 kilometres (4 nmi) wide and 19 kilometres (10 nmi) long, flowing north-northeast from the continental ice and terminating at the coast in a prominent tongue at the east side of Geologie Archipelago. It was first sighted in 1840 by the French expedition under Captain Jules Dumont d'Urville, although no glaciers were noted on d'Urville's chart of this coast but a formidable icy dike with perpendicular flanks of 37.7 m high according to the joined plate, corresponding to the glacier tongue. The glacier was photographed from the air by U.S. Navy Operation Highjump in January 1947. It was charted by the French Antarctic Expedition, 1949–51, and named after d'Urville's flagship, the Astrolabe.
The Astrolabe Glacier Tongue (66°42′S 140°5′E) is a prominent glacier tongue about 6 kilometres (3 nmi) wide and 7 kilometres (4 nmi) long, extending northeast from Astrolabe Glacier.Awad Bing language
Awad Bing, or Biliau, is an Austronesian language spoken by about 1,100 people in seven villages near Astrolabe Bay, Madang Province, Papua New Guinea. Almost all speakers also use Tok Pisin as a second language. Awad Bing is also spoken by a few Ngaing for trading purposes.Equatorium
An equatorium (plural, equatoria) is an astronomical calculating instrument. It can be used for finding the positions of the Moon, Sun, and planets without calculation, using a geometrical model to represent the position of a given celestial body.French ship Astrolabe (1811)
Astrolabe was a horse barge converted to an exploration ship of the French Navy and was originally named Coquille. She is famous for her travels with Jules Dumont d'Urville. The name derives from an early navigational instrument, the astrolabe, a precursor to the sextant.Ibn al-Saffar
Abu al‐Qasim Ahmad ibn Abd Allah ibn Umar al‐Ghafiqī ibn al-Saffar al‐Andalusi (born in Cordoba, died in the year 1035 at Denia), also known as Ibn al-Saffar (literally: son of the brass worker), was a Spanish-Arab astronomer in Al-Andalus. He worked at the school founded by his colleague Al-Majriti in Córdoba. His best-known work was a treatise on the astrolabe, a text that was in active use until the 15th century and influenced the work of Kepler. He also wrote a commentary on the Zij al-Sindhind, and measured the coordinates of Mecca.Ibn al-Saffar later influenced the works of Abu al-Salt.
Paul Kunitzsch argued that a Latin treatise on the astrolabe long attributed to Mashallah, and used by Chaucer to write A Treatise on the Astrolabe, is in fact written by Ibn al-Saffar.The exoplanet Saffar, also known as Upsilon Andromedae b, is named in his honor.Ibrahim ibn Said al-Sahli
Ibrahim Ibn Saîd al-Sahlì (11th century) was an Andalusian globe-maker, active from 1050 to 1090.
Ibrahim Ibn Saîd al-Sahlì worked in Valencia and Toledo in what is now Spain, and was mentioned in a list of mathematics students in Andalusia in a book written in 1068. Ibrahim Ibn Saîd al-Sahlì created the "astrolabe of Al-Sahli", an instrument to determine the positions of the stars on the sky, in the city of Tulaytulah (now Toledo, Spain) in the year 1066. He built four more astrolabes between 1067 and 1086. His first astrolabe was characterized by the peculiarity of its operation, as other astrolabes made in his time were not similar.Jules Dumont d'Urville
Jules Sébastien César Dumont d'Urville (French pronunciation: [ʒyl dymɔ̃ dyʁvil]; 23 May 1790 – 8 May 1842) was a French explorer, naval officer and rear admiral, who explored the south and western Pacific, Australia, New Zealand and Antarctica. As a botanist and cartographer he gave his name to several seaweeds, plants and shrubs, and places such as d'Urville Island in New Zealand.List of geological features on Mercury
List of geological features on Mercury is an itemization of mountains, valleys, craters and other landform features of the planet Mercury. Different types of features are named after different things: Mercurian ridges are called dorsa, and are named after astronomers who made detailed studies of the planet; valleys are called valles, and are named after radio telescope facilities; plains are called planitiae, and most are named after mythological names associated with Mercury; escarpments are called rupes and are named after the ships of famous explorers; long, narrow depressions are called fossae and are named after works of architecture.
See also list of craters on Mercury, list of albedo features on Mercury, and list of quadrangles on Mercury
Longitude is west longitude.Mahendra Sūri
Mahendra Sūri is the 14th century Jain astronomer who wrote the Yantraraja, the first Indian treatise on the astrolabe.Suri was a Jain. Jainism began around the sixth century BC and the religion had a strong influence on mathematics particularly in the last couple of centuries BC. By the time of Mahendra Suri, however, Jainism had lost support as a national religion and was much less vigorous. It had been influenced by Islam and in particular Islamic astronomy came to form a part of the background. However, Pingree in  writes that this filtering of Islamic astronomy into Indian culture was:-
... not allowed to affect in any way the structure of the traditional science.
Mahendra Suri was a pupil of Madana Suri. He is famed as the first person to write a Sanskrit treatise on the astrolabe. Ohashi writes in  of the early history of the astrolabe in the Delhi Sultanate in India:
The astrolabe was introduced into India at the time of Firuz Shah Tughluq (reign AD 1351 - 88), and Mahendra Suri wrote the first Sanskrit treatise on the astrolabe entitled Yantraraja (AD 1370). The Delhi Sultanate was established around 1200 and from that time on Muslim culture flourished in India. The ideas of Islamic astronomy began to appear in works in the Sanskrit language and it is the Islamic ideas on the astrolabe which Mahendra Suri wrote on in his famous text. It is clear from the various references in the text and also from the particular values that Mahendra Suri uses for the angle of the ecliptic etc. that his work is based on Islamic rather than traditional Indian astronomy works.Mariner's astrolabe
The mariner's astrolabe, also called sea astrolabe, was an inclinometer used to determine the latitude of a ship at sea by measuring the sun's noon altitude (declination) or the meridian altitude of a star of known declination. Not an astrolabe proper, the mariner's astrolabe was rather a graduated circle with an alidade used to measure vertical angles. They were designed to allow for their use on boats in rough water and/or in heavy winds, which astrolabes are ill-equipped to handle. In the sixteenth century, the instrument was also called a ring.Nastulus
Muḥammad ibn ʿAbd Allāh Nasṭūlus (or Basṭūlus) was a notable 10th-century astronomer and astrolabist. He is known for making the oldest surviving astrolabe, dated 927/928 AD. Another partially preserved astrolabe that bears his signature, "Made by Nasṭūlus in the year 315" of hijra (925 AD), contains the earliest known geographical list on an instrument.Very little is known about his life. His full name, based on a testimony given by a contemporary astronomer Abu Sa'id al-Sijzi, indicates that he was a Muslim. But some modern historians have suggested that his foreign last name may indicate that he was Greek or Nestorian.Nepean Point
Nepean Point is a hill with scenic lookout in Ottawa, Ontario, Canada, overlooking the Ottawa River, Parliament, the Canadian Museum of History, and other features of downtown Ottawa and Gatineau. It is located between the National Gallery of Canada and Alexandra Bridge.
At the peak of the hill is a statue of French explorer Samuel de Champlain holding his famous astrolabe upside-down. It was made by sculptor Hamilton MacCarthy in 1915.Previously, the statue also featured a kneeling First Nations (Anishinabe) scout, added in 1918 to "signify how the native people helped Champlain navigate through the waters of the Ottawa River", but this has been relocated to nearby Major's Hill Park.The small amphitheatre on the point is known as "Astrolabe Theatre", presumably a reference to Champlain.Ngero–Vitiaz languages
The Ngero–Vitiaz languages form a linkage of Austronesian languages in northern Papua New Guinea.Quadrant (instrument)
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.Tz database
The tz database is a collaborative compilation of information about the world's time zones, primarily intended for use with computer programs and operating systems. Paul Eggert is its current editor and maintainer, with the organizational backing of ICANN. The tz database is also known as tzdata, the zoneinfo database or IANA time zone database, and occasionally as the Olson database, referring to the founding contributor, Arthur David Olson.Its uniform naming convention for time zones, such as America/New_York and Europe/Paris, was designed by Paul Eggert. The database attempts to record historical time zones and all civil changes since 1970, the Unix time epoch. It also includes transitions such as daylight saving time, and also records leap seconds.The database, as well as some reference source code, is in the public domain. New editions of the database and code are published as changes warrant, usually several times per year.USS Guadalcanal (CVE-60)
USS Guadalcanal (CVE-60) was a Casablanca-class escort carrier of the United States Navy, which served during and after World War II. She was the first ship to carry her name. She was the flagship of Task Group 22.3, a hunter-killer group which captured the German submarine U-505 in 1944.USS Hollandia
USS Hollandia (CVE-97), formerly AVG-97 and ACV-97, was a Casablanca class escort carrier of the United States Navy.
Hollandia was launched under Maritime Commission contract as Astrolabe Bay (CVE-97) by Kaiser Co., Inc., Vancouver, Washington on 28 April 1944; sponsored by Mrs. William H. Wheat; renamed Hollandia on 30 May 1944; and commissioned on 1 June 1944, Captain Charles L. Lee in command.