An astrolabe (; ; ) is an astronomical instrument dating to ancient times. It serves as a star chart and physical model of the visible half-dome of the sky. Its various functions also make it an elaborate inclinometer and an analog calculation device capable of working out several kinds of problems in astronomy. In its simplest form it is a metal disc with a pattern of wires, cutouts, and perforations that allows a user to calculate astronomical positions precisely. It is able 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 Byzantine Empire, the Islamic Golden Age, the European Middle Ages and the Age of Discovery for all these purposes.
The astrolabe, which is a precursor to the sextant, is 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.
Etymology The Oxford English Dictionary gives the translation "star-taker" for the English word astrolabe and traces it through medieval Latin to the Greek word : , from : "star", and : "to take".
In the medieval Islamic world the Arabic word (i.e., astrolabe) was given various etymologies. In Arabic texts, the word is translated as (, ) – a direct translation of the Greek word.
Al-Biruni quotes and criticises medieval scientist Hamza al-Isfahani, who stated: "asturlab is an Arabisation of this Persian phrase" (, 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.
History Ancient era An astrolabe is essentially a plane (two-dimensional) version of an armillary sphere, which had already been invented in the Hellenistic period and had probably been used by Hipparchus to produce his star catalogue. Theon of Alexandria () wrote a detailed treatise on the astrolabe. The invention of the plane astrolabe is sometimes wrongly attributed to Theon's daughter Hypatia (born ; died Accessed 10 July 2014. but it is known to have been used much earlier. The misattribution comes from a misinterpretation of a statement in a letter written by Hypatia's pupil Synesius (), which mentions that Hypatia had taught him how to construct a plane astrolabe, but does not say that she invented it. Lewis argues that Ptolemy used an astrolabe to make the astronomical observations recorded in the Tetrabiblos. However, Emilie Savage-Smith notes "there is no convincing evidence that Ptolemy or any of his predecessors knew about the planispheric astrolabe".
In chapter 5.1 of the Almagest, Ptolemy describes the construction of an armillary sphere, and it is usually assumed that this was the instrument he used.
Astrolabes continued to be used in the Byzantine Empire. Christian philosopher John Philoponus wrote a treatise () on the astrolabe in Greek, which is the earliest extant treatise on the instrument.Modern editions of John Philoponus' treatise on the astrolabe are
or
repr. and translated into French
translated into English and included as part of
which was reprinted in 1976: Mesopotamian bishop Severus Sebokht also wrote a treatise on the astrolabe in the Syriac language during the mid-7th century. 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.
Medieval era Astrolabes were further developed in the medieval Islamic world, where Muslim astronomers introduced angular scales to the design,See p. 289 of adding circles indicating azimuths on the horizon. It was widely used throughout the Muslim world. Eighth-century mathematician Muhammad al-Fazari is the first person credited with building the astrolabe in the Islamic world.Richard Nelson Frye: Golden Age of Persia. p. 163 The earliest Arabic treatise on astrolabes was composed sometime around 815 CE.
The 10th century astronomer ʿAbd al-Raḥmān al-Ṣūfī wrote a text of 386 chapters on the astrolabe, which reportedly described more than 1,000 applications for its various functions. These ranged from the astrological, the astronomical, the religious, to navigation, seasonal and daily time-keeping, and tide tables. At the time of their use, astrology was widely considered as much of a serious science as astronomy, and study of the two went hand-in-hand. The astronomical interest varied between folk astronomy (of the pre-Islamic tradition in Arabia) which was concerned with celestial and seasonal observations, and mathematical astronomy, which would inform intellectual practices and precise calculations based on astronomical observations. In regard to the astrolabe's religious function, the demands of Islamic prayer times were to be astronomically determined to ensure precise daily timings, helping to schedule morning prayers (salat), and the qibla, the direction of Mecca towards which Muslims must pray, could also be determined by this device. In addition to this, the lunar calendar that was informed by the calculations of the astrolabe was of great significance to the religion of Islam, given that it determines the dates of important religious observances such as Ramadan.
The mathematical background was established by Muslim astronomer Albatenius in his treatise Kitab az-Zij which was translated into Latin by Plato Tiburtinus (De Motu Stellarum). The earliest surviving astrolabe is dated 927–928 CE (AH 315)
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. The earliest description of the spherical astrolabe dates 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.
The first known metal astrolabe in Western Europe is the Destombes astrolabe made from brass in the eleventh century in Portugal. 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.
Herman Contractus of Reichenau 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, Oxford. David A. King, historian of Islamic instrumentation, describes the universal astrolobe designed by Ibn al-Sarraj of Aleppo (a.k.a. Ahmad bin Abi Bakr; fl. 1328) as "the most sophisticated astronomical instrument from the entire Medieval and Renaissance periods".
English author Geoffrey Chaucer () 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 at sea. The use of the balesilha was promoted by Prince Henry (1394–1460) while navigating for Portugal.
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 () 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.
Greek painter Ieremias Palladas incorporated a sophisticated astrolabe in his 1612 painting depicting Catherine of Alexandria. The painting, entitled Catherine of Alexandria, in addition to the saint, showed a device labelled the 'system of the universe' (). The device featured the classical planets with their Greek names: Helios (Sun), Selene (Moon), Hermes (Mercury), Aphrodite (Venus), Ares (Mars), Zeus (Jupiter), and Cronos (Saturn). The depicted device also had celestial spheres, following the Ptolemaic model, and Earth was shown as a blue sphere with circles of geographic coordinates. A complicated line representing the axis of the Earth covered the entire instrument.
Sanskrit works Yantrarāja
In 1370, the first Indian treatise on the astrolabe was written by the Jain astronomer Mahendra Suri, titled Yantrarāja. With the support and patronage of Firuz Shah Tughlaq, Mahendra Sūri composed the first ever Sanskrit manual on astrolabes. It was Sūri who coined the Sanskrit name "Yantrarāja" ("the king of astronomical instruments") for the astrolabe and he also titled his manual on astrolabes as Yantrarāja. Sūri composed the manual in 1370 CE. Mahendra Sūri's student Malayendu Sūri composed a commentary on Yantrarāja in 1382. Two other commentaries on Yantrarāja are known, one by Gopirāja written in 1540 and other by Yajñeśvara in 1842.
The Yantrarāja manual in 128 verses is divided into five chapters. The first chapter Gaṇitādhyāya discusses the theory behind the astrolabe. The second chapter Yantraghatanādhyāya is devoted to descriptions of the various components of the astrolabe. The third chapter Yantraracanādhyāya describes the details of the construction of the astrolabe. The fourth chapter Yantrasodhanādhyāya discusses method for ascertaining whether the astrolabe has been properly constructed. It is in the fifth and final chapter Yantravicāraṇādhyāya one can see descriptions on how to use the instrument for observational and computational purposes. This chapter also dwells on the different types of astronomical and trigonometrical problems that can be solved using the astrolabe.
While Mahendra Sūri's manual is in 128 verses and contains no data in the form of tables, Malayendu Sūri's commentary is interspersed with neatly prepared tables.
Other Sanskrit works on astrolabe Over the centuries since the publication of Mahendra Sūri's Yantrarāja in 1370, several other Sanskrit manuals on the astrolabe have been composed. These include the following:
Yantra-rāja-adhikāra (Chapter 1 of Yantrakiraṇāvalī) by Padmanābha in 1423 Turya-yantra-prakāśa by Bhūdhara in 1572 Yantrarāja-vicāra-vimśādhyāyī by Nayanasukhopādhyāya in 1730 Yantrarāja-racanā by Savāī Jaya Siṃha (1688 - 1743) yantrarāja-kalpa by Mathurānātha Śukla (1782)
Astrolabes and clocks