The terms anno Domini and before Christ are used to label or number years in the Julian and Gregorian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord", but is presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ"; this calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years from the start of this epoch, BC denoting years before the start of the era. There is no year zero in this scheme, so the year AD 1 follows the year 1 BC; this dating system was devised in 525 by Dionysius Exiguus of Scythia Minor, but was not used until after 800. The Gregorian calendar is the most used calendar in the world today. For decades, it has been the unofficial global standard, adopted in the pragmatic interests of international communication and commercial integration, recognized by international institutions such as the United Nations.
Traditionally, English followed Latin usage by placing the "AD" abbreviation before the year number. However, BC is placed after the year number, which preserves syntactic order; the abbreviation is widely used after the number of a century or millennium, as in "fourth century AD" or "second millennium AD". Because BC is the English abbreviation for Before Christ, it is sometimes incorrectly concluded that AD means After Death, i.e. after the death of Jesus. However, this would mean that the approximate 33 years associated with the life of Jesus would neither be included in the BC nor the AD time scales. Terminology, viewed by some as being more neutral and inclusive of non-Christian people is to call this the Current or Common Era, with the preceding years referred to as Before the Common or Current Era. Astronomical year numbering and ISO 8601 avoid words or abbreviations related to Christianity, but use the same numbers for AD years; the Anno Domini dating system was devised in 525 by Dionysius Exiguus to enumerate the years in his Easter table.
His system was to replace the Diocletian era, used in an old Easter table because he did not wish to continue the memory of a tyrant who persecuted Christians. The last year of the old table, Diocletian 247, was followed by the first year of his table, AD 532; when he devised his table, Julian calendar years were identified by naming the consuls who held office that year—he himself stated that the "present year" was "the consulship of Probus Junior", 525 years "since the incarnation of our Lord Jesus Christ". Thus Dionysius implied that Jesus' incarnation occurred 525 years earlier, without stating the specific year during which his birth or conception occurred. "However, nowhere in his exposition of his table does Dionysius relate his epoch to any other dating system, whether consulate, year of the world, or regnal year of Augustus. Among the sources of confusion are: In modern times, incarnation is synonymous with the conception, but some ancient writers, such as Bede, considered incarnation to be synonymous with the Nativity.
The civil or consular year began on 1 January but the Diocletian year began on 29 August. There were inaccuracies in the lists of consuls. There were confused summations of emperors' regnal years, it is not known. Two major theories are that Dionysius based his calculation on the Gospel of Luke, which states that Jesus was "about thirty years old" shortly after "the fifteenth year of the reign of Tiberius Caesar", hence subtracted thirty years from that date, or that Dionysius counted back 532 years from the first year of his new table, it has been speculated by Georges Declercq that Dionysius' desire to replace Diocletian years with a calendar based on the incarnation of Christ was intended to prevent people from believing the imminent end of the world. At the time, it was believed by some that the resurrection of the dead and end of the world would occur 500 years after the birth of Jesus; the old Anno Mundi calendar theoretically commenced with the creation of the world based on information in the Old Testament.
It was believed that, based on the Anno Mundi calendar, Jesus was born in the year 5500 with the year 6000 of the Anno Mundi calendar marking the end of the world. Anno Mundi 6000 was thus equated with the resurrection and the end of the world but this date had passed in the time of Dionysius; the Anglo-Saxon historian the Venerable Bede, familiar with the work of Dionysius Exiguus, used Anno Domini dating in his Ecclesiastical History of the English People, completed in 731. In this same history, he used another Latin term, ante vero incarnationis dominicae tempus anno sexagesimo, equivalent to the English "before Christ", to identify years before the first year of this era. Both Dionysius and Bede regarded Anno Domini as beginning at the incarnation of Jesus, but "the distinction between Incarnation and Nativity was not drawn until the late 9th century, when in some places the Incarnation epoch was identified with Christ's conception, i.e. the Annunciation on March 25". On the continent of Europe, Anno
Nicolaus Copernicus was a Renaissance-era mathematician and astronomer who formulated a model of the universe that placed the Sun rather than the Earth at the center of the universe, in all likelihood independently of Aristarchus of Samos, who had formulated such a model some eighteen centuries earlier. The publication of Copernicus' model in his book De revolutionibus orbium coelestium, just before his death in 1543, was a major event in the history of science, triggering the Copernican Revolution and making a pioneering contribution to the Scientific Revolution. Copernicus was born and died in Royal Prussia, a region, part of the Kingdom of Poland since 1466. A polyglot and polymath, he obtained a doctorate in canon law and was a mathematician, physician, classics scholar, governor and economist. In 1517 he derived a quantity theory of money—a key concept in economics—and in 1519 he formulated an economic principle that came to be called Gresham's law. Nicolaus Copernicus was born on 19 February 1473 in the city of Thorn, in the province of Royal Prussia, in the Crown of the Kingdom of Poland.
His father was a merchant from Kraków and his mother was the daughter of a wealthy Toruń merchant. Nicolaus was the youngest of four children, his brother Andreas became an Augustinian canon at Frombork. His sister Barbara, named after her mother, became a Benedictine nun and, in her final years, prioress of a convent in Chełmno, his sister Katharina married the businessman and Toruń city councilor Barthel Gertner and left five children, whom Copernicus looked after to the end of his life. Copernicus never married and is not known to have had children, but from at least 1531 until 1539 his relations with Anna Schilling, a live-in housekeeper, were seen as scandalous by two bishops of Warmia who urged him over the years to break off relations with his "mistress". Copernicus' father's family can be traced to a village in Silesia near Nysa; the village's name has been variously spelled Kopernik, Copernic, Kopernic and today Koperniki. In the 14th century, members of the family began moving to various other Silesian cities, to the Polish capital, Kraków, to Toruń.
The father, Mikołaj the Elder the son of Jan, came from the Kraków line. Nicolaus was named after his father, who appears in records for the first time as a well-to-do merchant who dealt in copper, selling it in Danzig, he moved from Kraków to Toruń around 1458. Toruń, situated on the Vistula River, was at that time embroiled in the Thirteen Years' War, in which the Kingdom of Poland and the Prussian Confederation, an alliance of Prussian cities and clergy, fought the Teutonic Order over control of the region. In this war, Hanseatic cities like Danzig and Toruń, Nicolaus Copernicus's hometown, chose to support the Polish King, Casimir IV Jagiellon, who promised to respect the cities' traditional vast independence, which the Teutonic Order had challenged. Nicolaus' father was engaged in the politics of the day and supported Poland and the cities against the Teutonic Order. In 1454 he mediated negotiations between Poland's Cardinal Zbigniew Oleśnicki and the Prussian cities for repayment of war loans.
In the Second Peace of Thorn, the Teutonic Order formally relinquished all claims to its western province, which as Royal Prussia remained a region of the Crown of the Kingdom of Poland until the First and Second Partitions of Poland. Copernicus's father married Barbara Watzenrode, the astronomer's mother, between 1461 and 1464, he died about 1483. Nicolaus' mother, Barbara Watzenrode, was the daughter of a wealthy Toruń patrician and city councillor, Lucas Watzenrode the Elder, Katarzyna, mentioned in other sources as Katarzyna Rüdiger gente Modlibóg; the Modlibógs were a prominent Polish family, well known in Poland's history since 1271. The Watzenrode family, like the Kopernik family, had come from Silesia from near Świdnica, after 1360 had settled in Toruń, they soon became one of most influential patrician families. Through the Watzenrodes' extensive family relationships by marriage, Copernicus was related to wealthy families of Toruń, Gdańsk and Elbląg, to prominent Polish noble families of Prussia: the Czapskis, Działyńskis, Konopackis and Kościeleckis.
Lucas and Katherine had three children: Lucas Watzenrode the Younger, who would become Bishop of Warmia and Copernicus's patron. Lucas Watzenrode the Elder, a wealthy merchant and in 1439–62 president of the judicial bench, was a decided opponent of the Teutonic Knights. In 1453 he was the delegate from Toruń at the Grudziądz conference that planned the uprising against them. During the ensuing Thirteen Years' War, he supported the Prussian cities' war effort with substantial monetary subsidies, with political activity in Toruń and Danzig, by fighting in battles at Łasin and Malbork, he died in 1462. Lucas Watzenrode the Younger, the astronomer's maternal uncle and patron, was educated at the University of Kraków and at the universities of Cologne and Bologna, he was a bitter opponent of the Teutonic Order, its Grand Master once referred to him as "the devil incarn
The Banū Mūsā brothers, namely Abū Jaʿfar, Muḥammad ibn Mūsā ibn Shākir, Abū al‐Qāsim, Aḥmad ibn Mūsā ibn Shākir and Al-Ḥasan ibn Mūsā ibn Shākir, were three 9th-century Persian scholars who lived and worked in Baghdad. They are known for their Book of Ingenious Devices on automata and mechanical devices. Another important work of theirs is the Book on the Measurement of Plane and Spherical Figures, a foundational work on geometry, quoted by both Islamic and European mathematicians; the Banu Musa worked in astronomical observatories established in Baghdad by the Abbasid Caliph al-Ma'mun as well as doing research in the House of Wisdom. They participated in a 9th-century expedition to make geodesic measurements to determine the length of a degree; the Banu Musa were the three sons of Mūsā ibn Shākir, who earlier in life had been a highwayman and astronomer in Khorasan of unknown pedigree. After befriending al-Ma'mun, a governor of Khorasan and staying in Marw, Musa was employed as an astrologer and astronomer.
After his death, his young sons were looked after by the court of al-Maʾmūn. Al-Maʾmūn recognized the abilities of the three brothers and enrolled them in the famous House of Wisdom, a library and a translation center in Baghdad. Studying in the House of Wisdom under Yahya ibn Abi Mansur, they participated in the efforts to translate ancient Greek works into Arabic by sending for Greek texts from the Byzantines, paying large sums for their translation, learning Greek themselves. On such trips, Muhammad recruited the famous mathematician and translator Thābit ibn Qurra. At some point Hunayn ibn Ishaq was part of their team; the brothers sponsored many translators, who were paid about 500 dīnārs a month. Had it not been for the brothers' efforts, many of the Greek texts that they translated would have been lost and forgotten. After the death of al-Ma'mun, the Banu Musa continued to work under the Caliphs al-Mu'tasim, al-Wathiq, al-Mutawakkil. However, during the reign of al-Wathiq and al-Mutawakkil internal rivalries arose between the scholars in the House of Wisdom.
At some point the Banu Musa became enemies of al-Kindi and contributed to his persecution by al-Mutawakkil. They were employed by al-Mutawakkil to construct a canal for the new city of al-Jafariyya; the Banu Musa had a different view on circumference from the Greeks. In the research they translated, the Greeks looked at volume and area more in terms of ratios, rather than giving them an actual numerical value. Most of them based such measurements on another object's size. In one of their surviving publications, the Kitab Marifat Masahat Al-Ashkal Banu Musa gave volume and area number values; this is evidence that they were not just reproducing the Greek sources. They were building on concepts and coming up with some of their own original works; the most popular of their publications was the Kitāb al-Ḥiyal, the work of Aḥmad, the middle brother, was a book filled with one hundred mechanical devices. There were some real practical inventions in the book including a lamp that would mechanically dim, alternating fountains, a clamshell grab.
Eighty of these devices were described as "trick vessels" that showed a real mastery of mechanics, with a real focus on the use of light pressure. Some of the devices seem to be replications of earlier Greek works, but the rest were much more advanced than what the Greeks had done, they made many observations and contributions to the field of astronomy, writing nearly a dozen publications over their astronomical research. They made many observations on the moon. Al-Ma’mun had them go to a desert in Mesopotamia to measure the length of a degree, they measured the length of a year to be 365 days and 6 hours. Although they were not made famous by their politics, it should be noted that they did have interests outside the world of science the oldest brother Muhammad, they were employed by the caliphs for many different projects, including the canal mentioned above, they were a part of a team of 20 hired to build the town of al-D̲j̲aʿfariyya for al-Mutawakkil. Taking on these types of civil projects got them involved in the political scene in Baghdad.
However, the height of Muhammad's political activity in the palace came towards the end of his life, during a time when Turkish commanders were starting to take control of the state. After al-Mutawakkil died, Muhammad helped al-Mustaʿīn get the nomination instead of the caliph's brother; when the caliph's brother besieged the city of Baghdad, Muhammad was sent to estimate the size of the army, when the siege was over he was sent to get the terms of how al-Mustaʿīn would renounce the throne. This evidence shows, he was respected by the highest levels of authority at that time. The Banu Musa wrote 20 books, the majority of which are now lost. Most notable among their achievements is their work in the field of automation, which they utilized in toys and other entertaining creations, they have shown important advances over those of their Greek predecessors. The Book of Ingenious Devices describes 100 inventions. While designed for amusement purposes, they employ innovative engineering technologies such as one-way and two-way valves able to open and close by themselves, mechanical memories, devices to respond to feedback, delays.
Most of these devices were operated by water pressure. Qarasṭūn, a treatise on weight balance. On Mechanical Devices, a work on pneumatic dev
Claudius Ptolemy was a Greco-Roman mathematician, astronomer and astrologer. He lived in the city of Alexandria in the Roman province of Egypt, wrote in Koine Greek, held Roman citizenship; the 14th-century astronomer Theodore Meliteniotes gave his birthplace as the prominent Greek city Ptolemais Hermiou in the Thebaid. This attestation is quite late, and, according to Gerald Toomer, the translator of his Almagest into English, there is no reason to suppose he lived anywhere other than Alexandria, he died there around AD 168. Ptolemy wrote several scientific treatises, three of which were of importance to Byzantine and Western European science; the first is the astronomical treatise now known as the Almagest, although it was entitled the Mathematical Treatise and known as the Great Treatise. The second is the Geography, a thorough discussion of the geographic knowledge of the Greco-Roman world; the third is the astrological treatise in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day.
This is sometimes known as the Apotelesmatika but more known as the Tetrabiblos from the Greek meaning "Four Books" or by the Latin Quadripartitum. Ptolemaeus is a Greek name, it occurs once in Greek mythology, is of Homeric form. It was common among the Macedonian upper class at the time of Alexander the Great, there were several of this name among Alexander's army, one of whom made himself pharaoh in 323 BC: Ptolemy I Soter, the first king of the Ptolemaic Kingdom. All male kings of Hellenistic Egypt, until Egypt became a Roman province in 30 BC ending the Macedonian family's rule, were Ptolemies; the name Claudius is a Roman nomen. It would have suited custom if the first of Ptolemy's family to become a citizen took the nomen from a Roman called Claudius, responsible for granting citizenship. If, as was common, this was the emperor, citizenship would have been granted between AD 41 and 68; the astronomer would have had a praenomen, which remains unknown. The ninth-century Persian astronomer Abu Maʿshar presents Ptolemy as a member of Egypt's royal lineage, stating that the descendants of Alexander's general Ptolemy I, who ruled Egypt, were wise "and included Ptolemy the Wise, who composed the book of the Almagest".
Abu Maʿshar recorded a belief that a different member of this royal line "composed the book on astrology and attributed it to Ptolemy". We can evidence historical confusion on this point from Abu Maʿshar's subsequent remark "It is sometimes said that the learned man who wrote the book of astrology wrote the book of the Almagest; the correct answer is not known." There is little evidence on the subject of Ptolemy's ancestry, apart from what can be drawn from the details of his name. Ptolemy can be shown to have utilized Babylonian astronomical data, he was a Roman citizen, but was ethnically either a Greek or a Hellenized Egyptian. He was known in Arabic sources as "the Upper Egyptian", suggesting he may have had origins in southern Egypt. Arabic astronomers and physicists referred to him by his name in Arabic: بَطْلُمْيوس Baṭlumyus. Ptolemy's Almagest is the only surviving comprehensive ancient treatise on astronomy. Babylonian astronomers had developed arithmetical techniques for calculating astronomical phenomena.
Ptolemy, claimed to have derived his geometrical models from selected astronomical observations by his predecessors spanning more than 800 years, though astronomers have for centuries suspected that his models' parameters were adopted independently of observations. Ptolemy presented his astronomical models in convenient tables, which could be used to compute the future or past position of the planets; the Almagest contains a star catalogue, a version of a catalogue created by Hipparchus. Its list of forty-eight constellations is ancestral to the modern system of constellations, but unlike the modern system they did not cover the whole sky. Across Europe, the Middle East and North Africa in the Medieval period, it was the authoritative text on astronomy, with its author becoming an mythical figure, called Ptolemy, King of Alexandria; the Almagest was preserved, in Arabic manuscripts. Because of its reputation, it was sought and was translated twice into Latin in the 12th century, once in Sicily and again in Spain.
Ptolemy's model, like those of his predecessors, was geocentric and was universally accepted until the appearance of simpler heliocentric models during the scientific revolution. His Planetary Hypotheses went beyond the mathematical model of the Almagest to present a physical realization of the universe as a set of nested spheres, in which he used the epicycles of his planetary model to compute the dimensions of the universe, he estimated the Sun was at an average dis
Mīrzā Muhammad Tāraghay bin Shāhrukh, better known as Ulugh Beg, was a Timurid Sultan as well as an astronomer and mathematician. Ulugh Beg was notable for his work in astronomy-related mathematics, such as trigonometry and spherical geometry, as well as his general interests in the arts and intellectual activities, it is thought that he spoke five languages: Arabic, Turkic, a small amount of Chinese. During his rule the Timurid Empire achieved its cultural peak through Ulugh Beg's attention and patronage. Samarkand, captured and given to Ulugh Beg by his father Shah Rukh, became the headquarters of Muslim culture, he built the great Ulugh Beg Observatory in Samarkand between 1424 and 1429. It was considered by scholars to have been one of the finest observatories in the Islamic world at the time and the largest in Central Asia. Ulugh Beg was subsequently recognized as the most important observational astronomer from the 15th century by many scholars, he built the Ulugh Beg Madrasah in Samarkand and Bukhara, transforming the cities into cultural centers of learning in Central Asia.
However, Ulugh Beg's scientific expertise was not matched by his skills in governance. During his short reign, he failed to establish his authority; as a result, other rulers, including his family, took advantage of his lack of control and he was subsequently overthrown and assassinated. He was a grandson of the great conqueror and the oldest son of Shah Rukh, both of whom came from the Turkicized Barlas tribe of Transoxiana, his mother was a noblewoman named Goharshad, daughter of a member of the representative Turkic tribal aristocracy, Ghiyasuddin Tarkhan. Ulugh Beg was born in Sultaniyeh in Persia during Timur's invasion, his was given the name Mīrzā Muhammad Tāraghay. Ulugh Beg, the name he most known by, was not a personal name, but rather a moniker, which can be loosely translated as "Great Ruler" and is the Turkic equivalent of Timur's Perso-Arabic title Amīr-e Kabīr; as a child he wandered through a substantial part of the Middle East and India as his grandfather expanded his conquests in those areas.
After Timur's death, Shah Rukh moved the empire's capital to Herat. Sixteen-year-old Ulugh Beg subsequently became the governor of the former capital of Samarkand in 1409. In 1411, he was named the sovereign ruler of the whole of Mavarannahr; the teenaged ruler set out to turn the city into an intellectual center for the empire. Between 1417 and 1420, he built a madrasa on Registan Square in Samarkand, he invited numerous Islamic astronomers and mathematicians to study there; the madrasa building still survives. Ulugh Beg's most famous pupil in astronomy was Ali Qushchi. Qadi Zada al-Rumi was the most notable teacher at Ulugh Beg's madrasa and Jamshid al-Kashi, an astronomer came to join the staff, he was famous in the fields of medicine and poetry. He used to debate with other poets about contemporary social issues, he liked to debate in a poetic style, called "Bahribayt" among local poets. According to the Russian medical book "Mashkovskiy", Ulugh Beg discovered a mixture of alcohol with garlic preserving it to help treat conditions like diarrhea, stomach ache and intestine illnesses.
He offered advice for newly married couples, which indicate recipes containing nuts, dried apricot, dried grape etc. He claimed these to be useful to increase men's virility; this recipe has been given in Ibn Sina's books also. From an early age, astronomy piqued his interest after he paid a visit to what was still present of the Maragheh Observatory located in Maragheh, Iran; this is the observatory. In 1428, Ulugh Beg built an enormous observatory, called the Gurkhani Zij, similar to Tycho Brahe's Uraniborg as well as Taqi al-Din's observatory in Constantinople. Lacking telescopes to work with, he increased his accuracy by increasing the length of his sextant; the Fakhri sextant was the largest instrument at the observatory in Samarkand. There were many other astronomical instruments located at the observatory, but the Fakhri sextant is the most well-known instrument there; the purpose of the Fakhri sextant was to measure the transit altitudes of the stars. This was a measurement of the maximum altitude above the horizon of the stars.
It was only possible to use this device to measure the decline of natural objects in space. The image, which can be found in this article, shows the remaining portion of the instrument, which consists of the underground, lower portion of the instrument, not destroyed; the observatory built by Ulugh Beg was the most pervasive and well-known observatory throughout the Islamic world. With the instruments located in the observatory in Samarkand, Ulugh Beg composed a star catalogue consisting of 1018 stars, eleven less stars than are present in the star catalogue of Ptolemy. Ulugh Beg utilized dimensions from al-Sufi and based his star catalogue on a new analysis, autonomous from the data used by Ptolemy. Throughout his life as an astronomer, Ulugh Beg came to realize that there were multiple mistakes in the work and subsequent data of Ptolemy, in use for many years. Using it, he compiled the 1437
Abd al-Rahman al-Sufi
'Abd al-Rahman al-Sufi (Persian: عبدالرحمن صوفی was a Persian astronomer known as'Abd ar-Rahman as-Sufi,'Abd al-Rahman Abu al-Husayn,'Abdul Rahman Sufi, or'Abdurrahman Sufi and in the West as Azophi and Azophi Arabus. The lunar crater Azophi and the minor planet 12621 Alsufi are named after him. Al-Sufi published his famous Book of Fixed Stars in 964, describing much of his work, both in textual descriptions and pictures. Al-Biruni reports, he lived at the Buyid court in Isfahan.'Abd al-Rahman al-Sufi was one of the famous nine Muslim astronomers. His name implies, he lived at the court of Emir Adud ad-Daula in Isfahan and worked on translating and expanding Greek astronomical works the Almagest of Ptolemy. He contributed several corrections to Ptolemy's star list and did his own brightness and magnitude estimates which deviated from those in Ptolemy's work, he was a major translator into Arabic of the Hellenistic astronomy, centered in Alexandria, the first to attempt to relate the Greek with the traditional Arabic star names and constellations, which were unrelated and overlapped in complicated ways.
He identified the Large Magellanic Cloud, visible from Yemen, though not from Isfahan. He made the earliest recorded observation of the Andromeda Galaxy in 964 AD; these were the first galaxies other than the Milky Way to be observed from Earth. He observed that the ecliptic plane is inclined with respect to the celestial equator and more calculated the length of the tropical year, he observed and described the stars, their positions, their magnitudes and their colour, setting out his results constellation by constellation. For each constellation, he provided two drawings, one from the outside of a celestial globe, the other from the inside. Al-Sufi wrote about the astrolabe, finding numerous additional uses for it: he described over 1000 different uses, in areas as diverse as astronomy, horoscopes, surveying, Qibla, Salat prayer, etc. Since 2006, Astronomy Society of Iran – Amateur Committee hold an international Sufi Observing Competition in the memory of Al-Sufi; the first competition was held in 2006 in the north of Semnan Province and the second was held in the summer of 2008 in Ladiz near the Zahedan.
More than 100 attendees from Iran and Iraq participated in the event. List of Iranian scientists List of Muslim scientists Astronomy in Islam Liber locis stellarum fixarum, 964 da www.atlascoelestis.com Liber locis stellarum fixarum, 964, manoscritto del 1417 riprodotto il 1730 da www.atlascoelestis.com Ulug Beg in www.atlascoelestis.com Al-Sufi's constellations Al-Sūfī’s Book of the Constellations of the Fixed Stars and its Influence on Islamic and Western Celestial Cartography
A gnomon is the part of a sundial that casts a shadow. The term is used for a variety of purposes in other fields. A painted stick dating from 2300 BC was excavated at the astronomical site of Taosi is the oldest gnomon known in China; the gnomon was used in ancient China from the second century BC onward in order determine the changes in seasons and geographical latitude. The ancient Chinese used shadow measurements for creating calendars that are mentioned in several ancient texts. According to the collection of Zhou Chinese poetic anthologies Classic of Poetry, one of the distant ancestors of King Wen of the Zhou dynasty used to measure gnomon shadow lengths to determine the orientation around the 14th century BC; the ancient Greek philosopher Anaximander is credited with introducing this Babylonian instrument to the Ancient Greeks. The ancient Greek mathematician and astronomer Oenopides used the phrase drawn gnomon-wise to describe a line drawn perpendicular to another; the term was used for an L-shaped instrument like a steel square used to draw right angles.
This shape may explain its use to describe a shape formed by cutting a smaller square from a larger one. Euclid extended the term to the plane figure formed by removing a similar parallelogram from a corner of a larger parallelogram. Indeed, the gnomon is the increment between two successive figurate numbers, including square and triangular numbers; the ancient Greek mathematician and engineer Hero of Alexandria defined a gnomon as that which, when added to an entity, makes a new entity similar to the starting entity. In this sense Theon of Smyrna used it to describe a number which added to a polygonal number produces the next one of the same type; the most common use in this sense is an odd integer when seen as a figurate number between square numbers. Perforated gnomons projecting a pinhole image of the Sun were described in the Chinese Zhoubi Suanjing writings; the location of the bright circle can be measured to tell the time of year. In Arab and European cultures its invention was much attributed to Egyptian astronomer and mathematician Ibn Yunus around 1000 AD.
Italian astronomer and cosmographer Paolo Toscanelli is associated with the 1475 placement of a bronze plate with a round hole in the dome of the Cathedral of Santa Maria del Fiore in Florence to project an image of the Sun on the cathedral's floor. With markings on the floor it tells the exact time of each midday as well as the date of the summer solstice. Italian mathematician, engineer and geographer Leonardo Ximenes reconstructed the gnomon according to his new measurements in 1756. In the Northern Hemisphere, the shadow-casting edge of a sundial gnomon is oriented so that it points due northward and is parallel to the rotational axis of Earth; that is, it is inclined to the northern horizon at an angle that equals the latitude of the sundial's location. At present, such a gnomon should thus point precisely at Polaris, as this is within 1° of the north celestial pole. On some sundials, the gnomon is vertical; these were used in former times for observing the altitude of the Sun when on the meridian.
The style is the part of the gnomon. This can change as the Sun moves. For example, the upper west edge of the gnomon might be the style in the morning and the upper east edge might be the style in the afternoon. A three-dimensional gnomon is used in CAD and computer graphics as an aid to positioning objects in the virtual world. By convention, the x-axis direction is the y-axis green and the z-axis blue. NASA astronauts used a gnomon as a photographic tool to indicate local vertical and to display a color chart when they were working on the Moon's surface; the 1985 novel Masters of Atlantis by Charles Portis is a satirical chronicle of a fictional secret society called Gnomonism. In the book The Tower at the End of the World by Brad Strickland, a giant tower and thin stairs turn out to be the gnomon of a giant sundial; the island the tower is found on is called "Gnomon Island". The Gnomon of Saint-Sulpice inside the church of Saint Sulpice in Paris, built to assist in determining the date of Easter, was fictionalized as a "Rose Line" in the novel The Da Vinci Code.
The 2017 novel Gnomon by Nick Haraway is a novel set in a high-tech surveillance state. MarsDial Gazalé, Midhat J. Gnomons, from Pharaohs to Fractals, Princeton University Press, Princeton, 1999. ISBN 0-691-00514-1. Heath, Thomas Little, A History of Greek Mathematics, Dover publications, ISBN 9780486240732. Laërtius, The Lives and Opinions of Eminent Philosophers, trans. C. D. Yonge. London: Henry G. Bohn, 1853. Mayall, R. Newton. 1994, ISBN 0-486-41146-X Waugh, Albert E. Sundials: Their Theory and Construction, Dover Publications, Inc. 1973, ISBN 0-486-22947-5. The dictionary definition of gnomon at Wiktionary Media related to Gnomons at Wikimedia Commons