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An equatorium (plural, equatoria) is an astronomical calculating instrument. It can be used for finding the positions of the Moon, Sun, and planets without arithmetic operations, using a geometrical model to represent the position of a given celestial body.
In his comment on Ptolemy's Handy Tables, 4th century mathematician Theon of Alexandria introduced some diagrams to geometrically compute the position of the planets based on Ptolemy's epicyclical theory. The first description of the construction of a solar equatorium (as opposed to planetary) is contained in Proclus's fifth-century work Hypotyposis, [1] where he gives instructions on how to construct one in wood or bronze. [2]
The earliest known descriptions of planetary equatoria are in the Latin translation of an early eleventh century text by Ibn al‐Samḥ and a 1080/1081 [3] treatise by al-Zarqālī, contained in the Libros del saber de astronomia (Books of the knowledge of astronomy), a Castilian compilation of astronomical works collected under the patronage of Alfonso X of Castile in the thirteenth century. [2]
The Theorica Planetarum (c. 1261–1264) by Campanus of Novara is the earliest extant description of the construction of an equatorium in Latin Europe. [4] Campanus' instrument resembled an astrolabe, with several interchangeable plates within a mater. The best manuscripts of Campanus' treatise contain paper and parchment equatoria with moveable parts. [2]
The history of the equatorium does not just end after the 11th century, but it inspired a more diverse invention called “The Albion”. The Albion is an astronomical instrument invented by Richard of Wallingford at the beginning of the 14th century. [5] It has various functional uses such as that of the equatorium for planetary and conjunction computations. It can calculate when eclipses will occur. The Albion is made up of 18 different scales which makes it extremely complex in comparison to the equatorium. The history of this instrument is still disputed to this day, as the only Albion from the past is both unnamed and unmarked. [5]
The roots of the equatorium lie in the astrolabe. The history of the astrolabe dates back to roughly 220 BC in the works of Hipparchus. [6] The difference between the two instruments is that the astrolabe measures the time and position of the sun and stars at a specific location in time. [7] In contrast, the equatorium is used to calculate the past or future positions of the planets and celestial bodies according to the planetary theory of Ptolemy.
The equatorium can further be specialized depending on the epicycle. There are three possible epicycles that can be adjusted to serve for planetary positions in three groups: the moon, the stars, and the sun. The sun was considered a planet in the Ptolemaic system, hence why the equatorium could be used to determine its position. [8] Through the use of Ptolemy's model, astronomers were able to make a single instrument with various capabilities that catered to the belief that the solar system had the earth at the center. In fact, specialized equatoriums had astrological aspects of medicine, as the orientation of planets gave insight to zodiac signs which helped some doctors cater medical treatments to patients.
At least 15 minutes was needed to calculate the planetary position with the use of a table for each celestial body. [9] A horoscope of that era would have required the positions of seven astronomical objects, requiring nearly two hours of manual calculation time.
Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way.
Hipparchus was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equinoxes. Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes, Greece. He is known to have been a working astronomer between 162 and 127 BC.
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory: vestiges of these are still found in astrology, a discipline long interwoven with public and governmental astronomy. It was not completely separated in Europe during the Copernican Revolution starting in 1543. In some cultures, astronomical data was used for astrological prognostication.
The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south of the ecliptic, which is the apparent path of the Sun across the celestial sphere over the course of the year. The orbital paths of the Moon and major planets are within the belt of the zodiac.
An orrery is a mechanical model of the Solar System that illustrates or predicts the relative positions and motions of the planets and moons, usually according to the heliocentric model. It may also represent the relative sizes of these bodies; however, since accurate scaling is often not practical due to the actual large ratio differences, a subdued approximation may be used instead. Though the Greeks had working planetaria, the first orrery that was a planetarium of the modern era was produced in 1713, and one was presented to Charles Boyle, 4th Earl of Orrery – hence the name. They are typically driven by a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms.
An astrolabe is an astronomical instrument dating to ancient times. It serves as a star chart and physical model of visible heavenly bodies. 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. Historically used by astronomers, 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, 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.
In astronomy, the geocentric model is a superseded description of the Universe with Earth at the center. Under most geocentric models, the Sun, Moon, stars, and planets all orbit Earth. The geocentric model was the predominant description of the cosmos in many European ancient civilizations, such as those of Aristotle in Classical Greece and Ptolemy in Roman Egypt, as well as during the Islamic Golden Age.
In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets. In particular it explained the apparent retrograde motion of the five planets known at the time. Secondarily, it also explained changes in the apparent distances of the planets from the Earth.
The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths, written by Claudius Ptolemy in Koine Greek. One of the most influential scientific texts in history, it canonized a geocentric model of the Universe that was accepted for more than 1,200 years from its origin in Hellenistic Alexandria, in the medieval Byzantine and Islamic worlds, and in Western Europe through the Middle Ages and early Renaissance until Copernicus. It is also a key source of information about ancient Greek astronomy.
In astronomy and celestial navigation, an ephemeris is a book with tables that gives the trajectory of naturally occurring astronomical objects as well as artificial satellites in the sky, i.e., the position over time. Historically, positions were given as printed tables of values, given at regular intervals of date and time. The calculation of these tables was one of the first applications of mechanical computers. Modern ephemerides are often provided in electronic form. However, printed ephemerides are still produced, as they are useful when computational devices are not available.
The celestial spheres, or celestial orbs, were the fundamental entities of the cosmological models developed by Plato, Eudoxus, Aristotle, Ptolemy, Copernicus, and others. In these celestial models, the apparent motions of the fixed stars and planets are accounted for by treating them as embedded in rotating spheres made of an aetherial, transparent fifth element (quintessence), like gems set in orbs. Since it was believed that the fixed stars did not change their positions relative to one another, it was argued that they must be on the surface of a single starry sphere.
Abū Isḥāq Ibrāhīm ibn Yaḥyā al-Naqqāsh al-Zarqālī al-Tujibi ; also known as Al-Zarkali or Ibn Zarqala (1029–1100), was an Arab maker of astronomical instruments and an astrologer from the western part of the Islamic world.
The Toledan Tables, or Tables of Toledo, were astronomical tables which were used to predict the movements of the Sun, Moon and planets relative to the fixed stars. They were a collection of mathematic tables that describe different aspects of the cosmos including prediction of calendar dates, times of cosmic events, and cosmic motion.
ʿAbu al-Ḥasan Alāʾ al‐Dīn bin Alī bin Ibrāhīm bin Muhammad bin al-Matam al-Ansari known as Ibn al-Shatir or Ibn ash-Shatir was an Arab astronomer, mathematician and engineer. He worked as muwaqqit in the Umayyad Mosque in Damascus and constructed a sundial for its minaret in 1371/72.
Medieval Islamic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age, and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and later in the Far East and India. It closely parallels the genesis of other Islamic sciences in its assimilation of foreign material and the amalgamation of the disparate elements of that material to create a science with Islamic characteristics. These included Greek, Sassanid, and Indian works in particular, which were translated and built upon.
Ancient Greek astronomy is the astronomy written in the Greek language during classical antiquity. Greek astronomy is understood to include the Ancient Greek, Hellenistic, Greco-Roman, and late antique eras. It is not limited geographically to Greece or to ethnic Greeks, as the Greek language had become the language of scholarship throughout the Hellenistic world following the conquests of Alexander. This phase of Greek astronomy is also known as Hellenistic astronomy, while the pre-Hellenistic phase is known as Classical Greek astronomy. During the Hellenistic and Roman periods, many of the Greek and non-Greek astronomers working in the Greek tradition studied at the Museum and the Library of Alexandria in Ptolemaic Egypt.
Babylonian astronomy was the study or recording of celestial objects during the early history of Mesopotamia.
Aryabhatiya or Aryabhatiyam, a Sanskrit astronomical treatise, is the magnum opus and only known surviving work of the 5th century Indian mathematician Aryabhata. Philosopher of astronomy Roger Billard estimates that the book was composed around 510 CE based on historical references it mentions.
Copernican heliocentrism is the astronomical model developed by Nicolaus Copernicus and published in 1543. This model positioned the Sun at the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular paths, modified by epicycles, and at uniform speeds. The Copernican model displaced the geocentric model of Ptolemy that had prevailed for centuries, which had placed Earth at the center of the Universe.
The Equatorie of the Planetis is a 14th-century scientific work which describes the construction and use of an equatorium. It was first studied in the early 1950s by Derek J. Price, and was formerly attributed to Geoffrey Chaucer. However, in 2014 it was shown to be written in the hand of the St Albans monk John Westwyk. It is largely written in Middle English, with some additions in Latin. It is accompanied by extensive astronomical tables, with Latin headings and annotations.
