Celestial Orb
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The celestial spheres, or celestial orbs, were the fundamental entities of the
cosmological Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe, the cosmos. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', with the meaning of "a speaking of the wo ...
models developed by
Plato Plato ( ; Greek language, Greek: , ; born  BC, died 348/347 BC) was an ancient Greek philosopher of the Classical Greece, Classical period who is considered a foundational thinker in Western philosophy and an innovator of the writte ...
, Eudoxus,
Aristotle Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...
,
Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
,
Copernicus Nicolaus Copernicus (19 February 1473 – 24 May 1543) was a Renaissance polymath who formulated a mathematical model, model of Celestial spheres#Renaissance, the universe that placed heliocentrism, the Sun rather than Earth at its cen ...
, and others. In these celestial models, the apparent motions of the
fixed stars In astronomy, the fixed stars () are the luminary points, mainly stars, that appear not to move relative to one another against the darkness of the night sky in the background. This is in contrast to those lights visible to the naked eye, name ...
and
planets A planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the te ...
are accounted for by treating them as embedded in rotating spheres made of an aetherial, transparent fifth element (
quintessence Quintessence, or quintessential, or fifth essence, may refer to: Cosmology * Aether (classical element), in medieval cosmology and science, the fifth element that fills the universe beyond the terrestrial sphere * Quintessence (physics), a hypo ...
), like gems set in orbs. Since it was believed that the fixed stars were unchanging in their positions relative to one another, it was argued that they must be on the surface of a single starry sphere.


Context

In modern thought, the orbits of the planets are viewed as the paths of those planets through mostly empty space. Ancient and medieval thinkers, however, considered the celestial orbs to be thick spheres of rarefied matter nested one within the other, each one in complete contact with the sphere above it and the sphere below.Lindberg, ''Beginnings of Western Science'', p. 251. When scholars applied Ptolemy's epicycles, they presumed that each planetary sphere was exactly thick enough to accommodate them. By combining this nested sphere model with astronomical observations, scholars calculated what became generally accepted values at the time for the distances to the Sun: about , to the other planets, and to the edge of the universe: about . The nested sphere model's distances to the Sun and planets differ significantly from modern measurements of the distances, and the
size of the universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...
is now known to be inconceivably large and continuously expanding. Albert Van Helden has suggested that from about 1250 until the 17th century, virtually all educated Europeans were familiar with the Ptolemaic model of "nesting spheres and the cosmic dimensions derived from it". Even following the adoption of Copernicus's
heliocentric model Heliocentrism (also known as the heliocentric model) is a superseded astronomical model in which the Earth and planets orbit around the Sun at the center of the universe. Historically, heliocentrism was opposed to geocentrism, which placed th ...
of the universe, new versions of the celestial sphere model were introduced, with the planetary spheres following this sequence from the Sun at the centre: Mercury, Venus, Earth-Moon, Mars, Jupiter and Saturn. Mainstream belief in the theory of celestial spheres did not survive the
Scientific Revolution The Scientific Revolution was a series of events that marked the emergence of History of science, modern science during the early modern period, when developments in History of mathematics#Mathematics during the Scientific Revolution, mathemati ...
. In the early 1600s,
Kepler Johannes Kepler (27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws of p ...
continued to discuss celestial spheres, although he did not consider that the planets were carried by the spheres but held that they moved in elliptical paths described by
Kepler's laws of planetary motion In astronomy, Kepler's laws of planetary motion, published by Johannes Kepler in 1609 (except the third law, which was fully published in 1619), describe the orbits of planets around the Sun. These laws replaced circular orbits and epicycles in ...
. In the late 1600s, Greek and medieval theories concerning the motion of terrestrial and celestial objects were replaced by
Newton's law of universal gravitation Newton's law of universal gravitation describes gravity as a force by stating that every particle attracts every other particle in the universe with a force that is Proportionality (mathematics)#Direct proportionality, proportional to the product ...
and
Newtonian mechanics Newton's laws of motion are three physical laws that describe the relationship between the motion of an object and the forces acting on it. These laws, which provide the basis for Newtonian mechanics, can be paraphrased as follows: # A body r ...
, which explain how Kepler's laws arise from the gravitational attraction between bodies.


History


Early ideas of spheres and circles

In
Greek antiquity Ancient Greece () was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity (), that comprised a loose collection of culturally and linguistically rel ...
the ideas of celestial spheres and rings first appeared in the cosmology of
Anaximander Anaximander ( ; ''Anaximandros''; ) was a Pre-Socratic philosophy, pre-Socratic Ancient Greek philosophy, Greek philosopher who lived in Miletus,"Anaximander" in ''Chambers's Encyclopædia''. London: George Newnes Ltd, George Newnes, 1961, Vol. ...
in the early 6th century BC. In his cosmology both the Sun and Moon are circular open vents in tubular rings of fire enclosed in tubes of condensed air; these rings constitute the rims of rotating chariot-like wheels pivoting on the Earth at their centre. The fixed stars are also open vents in such wheel rims, but there are so many such wheels for the stars that their contiguous rims all together form a continuous spherical shell encompassing the Earth. All these wheel rims had originally been formed out of an original
sphere of fire Sphere of fire is the name given in Ptolemaic astronomy to the sphere intervening between, and separating, the Earth and the Moon. Traditional concept Building on Empedocles's vision of the world as a four-level cake of stacked fundamental elemen ...
wholly encompassing the Earth, which had disintegrated into many individual rings. Hence, in Anaximander's
cosmogony Cosmogony is any model concerning the origin of the cosmos or the universe. Overview Scientific theories In astronomy, cosmogony is the study of the origin of particular astrophysical objects or systems, and is most commonly used in ref ...
, in the beginning was the sphere, out of which celestial rings were formed, from some of which the stellar sphere was in turn composed. As viewed from the Earth, the ring of the Sun was highest, that of the Moon was lower, and the sphere of the stars was lowest. Following Anaximander, his pupil Anaximenes () held that the stars, Sun, Moon, and planets are all made of fire. But whilst the stars are fastened on a revolving crystal sphere like nails or studs, the Sun, Moon, and planets, and also the Earth, all just ride on air like leaves because of their breadth. And whilst the fixed stars are carried around in a complete circle by the stellar sphere, the Sun, Moon and planets do not revolve under the Earth between setting and rising again like the stars do, but rather on setting they go laterally around the Earth like a cap turning halfway around the head until they rise again. And unlike Anaximander, he relegated the fixed stars to the region most distant from the Earth. The most enduring feature of Anaximenes' cosmos was its conception of the stars being fixed on a crystal sphere as in a rigid frame, which became a fundamental principle of cosmology down to Copernicus and Kepler. After Anaximenes,
Pythagoras Pythagoras of Samos (;  BC) was an ancient Ionian Greek philosopher, polymath, and the eponymous founder of Pythagoreanism. His political and religious teachings were well known in Magna Graecia and influenced the philosophies of P ...
,
Xenophanes Xenophanes of Colophon ( ; ; – c. 478 BC) was a Greek philosopher, theologian, poet, and critic of Homer. He was born in Ionia and travelled throughout the Greek-speaking world in early classical antiquity. As a poet, Xenophanes was known f ...
and
Parmenides Parmenides of Elea (; ; fl. late sixth or early fifth century BC) was a Pre-Socratic philosophy, pre-Socratic ancient Greece, Greek philosopher from Velia, Elea in Magna Graecia (Southern Italy). Parmenides was born in the Greek colony of Veli ...
all held that the universe was spherical. And much later in the fourth century BC Plato's '' Timaeus'' proposed that the body of the cosmos was made in the most perfect and uniform shape, that of a sphere containing the fixed stars. But it posited that the planets were spherical bodies set in rotating bands or rings rather than wheel rims as in Anaximander's cosmology.


Emergence of the planetary spheres

Instead of bands, Plato's student Eudoxus developed a planetary model using
concentric spheres The cosmological model of concentric (or homocentric) spheres, developed by Eudoxus of Cnidus, Eudoxus, Callippus, and Aristotle, employed celestial spheres all geocentric model, centered on the Earth. In this respect, it differed from the epicycle ...
for all the planets, with three spheres each for his models of the Moon and the Sun and four each for the models of the other five planets, thus making 26 spheres in all.Lloyd, "Heavenly aberrations," p. 173.
Callippus Callippus (; ; c. 370 BC – c. 300 BC) was a Greek astronomer and mathematician. Biography Callippus was born at Cyzicus, and studied under Eudoxus of Cnidus at the Academy of Plato. He also worked with Aristotle at the Lyceum, which means tha ...
modified this system, using five spheres for his models of the Sun, Moon, Mercury, Venus, and Mars and retaining four spheres for the models of Jupiter and Saturn, thus making 33 spheres in all. Each planet is attached to the innermost of its own particular set of spheres. Although the models of Eudoxus and Callippus qualitatively describe the major features of the motion of the planets, they fail to account exactly for these motions and therefore cannot provide quantitative predictions. Although historians of Greek science have traditionally considered these models to be merely geometrical representations, recent studies have proposed that they were also intended to be physically real or have withheld judgment, noting the limited evidence to resolve the question. In his ''
Metaphysics Metaphysics is the branch of philosophy that examines the basic structure of reality. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the conceptual framework of ...
'',
Aristotle Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...
developed a physical cosmology of spheres, based on the mathematical models of Eudoxus. In Aristotle's fully developed celestial model, the spherical Earth is at the centre of the universe and the planets are moved by either 47 or 55 interconnected spheres that form a unified planetary system, whereas in the models of Eudoxus and Callippus each planet's individual set of spheres were not connected to those of the next planet. Aristotle says the exact number of spheres, and hence the number of movers, is to be determined by astronomical investigation, but he added additional spheres to those proposed by Eudoxus and Callippus, to counteract the motion of the outer spheres. Aristotle considers that these spheres are made of an unchanging fifth element, the
aether Aether, æther or ether may refer to: Historical science and mythology * Aether (mythology), the personification of the bright upper sky * Aether (classical element), the material believed to fill the universe above the terrestrial sphere ** A ...
. Each of these concentric spheres is moved by its own god—an unchanging divine unmoved mover, and who moves its sphere simply by virtue of being loved by it. In his ''
Almagest The ''Almagest'' ( ) is a 2nd-century Greek mathematics, mathematical and Greek astronomy, astronomical treatise on the apparent motions of the stars and planetary paths, written by Ptolemy, Claudius Ptolemy ( ) in Koine Greek. One of the most i ...
'', the astronomer
Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
(fl. c. 150 AD) developed geometrical predictive models of the motions of the stars and planets and extended them to a unified physical model of the
cosmos The cosmos (, ; ) is an alternative name for the universe or its nature or order. Usage of the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos is studied in cosmologya broad discipline covering ...
in his ''Planetary hypotheses''. By using eccentrics and epicycles, his geometrical model achieved greater mathematical detail and predictive accuracy than had been exhibited by earlier concentric spherical models of the cosmos. In Ptolemy's physical model, each planet is contained in two or more spheres,Neugebauer, ''History of Ancient Mathematical Astronomy'', vol. 2, pp. 917–926. but in Book 2 of his ''Planetary Hypotheses'' Ptolemy depicted thick circular slices rather than spheres as in its Book 1. One sphere/slice is the
deferent In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle (, meaning "circle moving on another circle") was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, ...
, with a centre offset somewhat from the Earth; the other sphere/slice is an
epicycle In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle (, meaning "circle moving on another circle") was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, ...
embedded in the deferent, with the planet embedded in the epicyclical sphere/slice. Ptolemy's model of nesting spheres provided the general dimensions of the cosmos, the greatest distance of Saturn being 19,865 times the radius of the Earth and the distance of the fixed stars being at least 20,000 Earth radii. The planetary spheres were arranged outwards from the spherical, stationary Earth at the centre of the universe in this order: the spheres of the
Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
, Mercury,
Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...
,
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
,
Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...
,
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
, and
Saturn Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...
. In more detailed models the seven planetary spheres contained other secondary spheres within them. The planetary spheres were followed by the stellar sphere containing the fixed stars; other scholars added a ninth sphere to account for the
precession of the equinoxes In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's Rotation around a fixed axis, rotational axis. In the absence of precession, the astronomical body's orbit would show ...
, a tenth to account for the supposed trepidation of the equinoxes, and even an eleventh to account for the changing
obliquity of the ecliptic In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbital ...
. In antiquity the order of the lower planets was not universally agreed. Plato and his followers ordered them Moon, Sun, Mercury, Venus, and then followed the standard model for the upper spheres. Others disagreed about the relative place of the spheres of Mercury and Venus: Ptolemy placed both of them beneath the Sun with Venus above Mercury, but noted others placed them both above the Sun; some medieval thinkers, such as
al-Bitruji Nūr al-Dīn ibn Isḥaq al-Biṭrūjī (, died c. 1204), known in the West by the Latinized name of Alpetragius, was an Arab astronomer and qadi in al-Andalus. Al-Biṭrūjī was the first astronomer to present the concentric spheres model as an ...
, placed the sphere of Venus above the Sun and that of Mercury below it.


Middle Ages


Astronomical discussions

A series of astronomers, beginning with the Muslim astronomer al-Farghānī, used the Ptolemaic model of nesting spheres to compute distances to the stars and planetary spheres. Al-Farghānī's distance to the stars was 20,110 Earth radii which, on the assumption that the radius of the Earth was , came to . An introduction to Ptolemy's ''Almagest'', the ''Tashil al-Majisti'', believed to be written by
Thābit ibn Qurra Thābit ibn Qurra (full name: , , ; 826 or 836 – February 19, 901), was a scholar known for his work in mathematics, medicine, astronomy, and translation. He lived in Baghdad in the second half of the ninth century during the time of the Abba ...
, presented minor variations of Ptolemy's distances to the celestial spheres. In his ''
Zij A ' () is an Islamic astronomical book that tabulates parameters used for astronomical calculations of the positions of the sun, moon, stars, and planets. Etymology The name ''zīj'' is derived from the Middle Persian term ' or ' "cord". Th ...
'',
Al-Battānī Al-Battani (before 858929), archaically Latinized as Albategnius, was a Muslim astronomer, astrologer, geographer and mathematician, who lived and worked for most of his life at Raqqa, now in Syria. He is considered to be the greatest and mos ...
presented independent calculations of the distances to the planets on the model of nesting spheres, which he thought was due to scholars writing after Ptolemy. His calculations yielded a distance of 19,000 Earth radii to the stars.Van Helden, ''Measuring the Universe'', pp. 31–2. Around the turn of the millennium, the Arabic astronomer and polymath Ibn al-Haytham (Alhacen) presented a development of Ptolemy's
geocentric model In astronomy, the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded scientific theories, superseded description of the Universe with Earth at the center. Under most geocentric m ...
s in terms of nested spheres. Despite the similarity of this concept to that of Ptolemy's ''Planetary Hypotheses'', al-Haytham's presentation differs in sufficient detail that it has been argued that it reflects an independent development of the concept. In chapters 15–16 of his ''
Book of Optics The ''Book of Optics'' (; or ''Perspectiva''; ) is a seven-volume treatise on optics and other fields of study composed by the medieval Arab scholar Ibn al-Haytham, known in the West as Alhazen or Alhacen (965–c. 1040 AD). The ''Book ...
'', Ibn al-Haytham also said that the celestial spheres do not consist of
solid Solid is a state of matter where molecules are closely packed and can not slide past each other. Solids resist compression, expansion, or external forces that would alter its shape, with the degree to which they are resisted dependent upon the ...
matter. Near the end of the twelfth century, the Spanish Muslim astronomer al-Bitrūjī (Alpetragius) sought to explain the complex motions of the planets without Ptolemy's epicycles and eccentrics, using an Aristotelian framework of purely concentric spheres that moved with differing speeds from east to west. This model was much less accurate as a predictive astronomical model, but it was discussed by later European astronomers and philosophers. In the thirteenth century the astronomer al-'Urḍi proposed a radical change to Ptolemy's system of nesting spheres. In his ''Kitāb al-Hayáh'', he recalculated the distance of the planets using parameters which he redetermined. Taking the distance of the Sun as 1,266 Earth radii, he was forced to place the sphere of Venus above the sphere of the Sun; as a further refinement, he added the planet's diameters to the thickness of their spheres. As a consequence, his version of the nesting spheres model had the sphere of the stars at a distance of 140,177 Earth radii. About the same time, scholars in European
universities A university () is an educational institution, institution of tertiary education and research which awards academic degrees in several Discipline (academia), academic disciplines. ''University'' is derived from the Latin phrase , which roughly ...
began to address the implications of the rediscovered philosophy of Aristotle and astronomy of Ptolemy. Both astronomical scholars and popular writers considered the implications of the nested sphere model for the dimensions of the universe.
Campanus of Novara Campanus of Novara ( 1220 – 1296) was an Italian mathematician, astronomer, astrologer, and physician who is best known for his work on Euclid's ''Elements''. In his writings he refers to himself as Campanus Nouariensis; contemporary document ...
's introductory astronomical text, the ''Theorica planetarum'', used the model of nesting spheres to compute the distances of the various planets from the Earth, which he gave as 22,612 Earth radii or . In his ''
Opus Majus The (Latin for "Greater Work") is the most important work of Roger Bacon. It was written in Medieval Latin, at the request of Pope Clement IV, to explain the work that Bacon had undertaken. The 878-page treatise ranges over all aspects of natur ...
'',
Roger Bacon Roger Bacon (; or ', also '' Rogerus''; ), also known by the Scholastic accolades, scholastic accolade ''Doctor Mirabilis'', was a medieval English polymath, philosopher, scientist, theologian and Franciscans, Franciscan friar who placed co ...
cited Al-Farghānī's distance to the stars of 20,110 Earth radii, or , from which he computed the circumference of the universe to be . Clear evidence that this model was thought to represent physical reality is the accounts found in Bacon's ''Opus Majus'' of the time needed to walk to the Moon and in the popular
Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman Conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English pe ...
''
South English Legendary South English legendaries are compilations of versified saints' lives written in southern dialects of Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman Conquest of 1066, until ...
'', that it would take 8,000 years to reach the highest starry heaven. General understanding of the dimensions of the universe derived from the nested sphere model reached wider audiences through the presentations in Hebrew by
Moses Maimonides Moses ben Maimon (1138–1204), commonly known as Maimonides (, ) and also referred to by the Hebrew acronym Rambam (), was a Sephardic rabbi and philosopher who became one of the most prolific and influential Torah scholars of the Middle A ...
, in French by Gossuin of Metz, and in Italian by
Dante Alighieri Dante Alighieri (; most likely baptized Durante di Alighiero degli Alighieri; – September 14, 1321), widely known mononymously as Dante, was an Italian Italian poetry, poet, writer, and philosopher. His ''Divine Comedy'', originally called ...
.


Philosophical and theological discussions

Philosophers were less concerned with such mathematical calculations than with the nature of the celestial spheres, their relation to revealed accounts of created nature, and the causes of their motion. Adi Setia describes the debate among Islamic scholars in the twelfth century, based on the commentary of
Fakhr al-Din al-Razi Fakhr al-Dīn al-Rāzī () or Fakhruddin Razi () (1149 or 1150 – 1209), often known by the sobriquet Sultan of the Theologians, was an influential Iranian and Muslim polymath, scientist and one of the pioneers of inductive logic. He wrote var ...
about whether the celestial spheres are real, concrete physical bodies or "merely the abstract circles in the heavens traced out… by the various stars and planets." Setia points out that most of the learned, and the astronomers, said they were solid spheres "on which the stars turn… and this view is closer to the apparent sense of the Qur'anic verses regarding the celestial orbits." However, al-Razi mentions that some, such as the Islamic scholar Dahhak, considered them to be abstract. Al-Razi himself, was undecided, he said: "In truth, there is no way to ascertain the characteristics of the heavens except by authority f divine revelation or prophetic traditions" Setia concludes: "Thus it seems that for al-Razi (and for others before and after him), astronomical models, whatever their utility or lack thereof for ordering the heavens, are not founded on sound rational proofs, and so no intellectual commitment can be made to them insofar as description and explanation of celestial realities are concerned." Christian and Muslim philosophers modified Ptolemy's system to include an unmoved outermost region, the
empyrean In ancient European cosmologies inspired by Aristotle, the Empyrean heaven, Empyreal or simply the Empyrean, was the place in the highest heaven which was supposed to be occupied by the element of fire (or aether in Aristotle's natural philos ...
heaven, which came to be identified as the dwelling place of
God In monotheistic belief systems, God is usually viewed as the supreme being, creator, and principal object of faith. In polytheistic belief systems, a god is "a spirit or being believed to have created, or for controlling some part of the un ...
and all the elect. Medieval Christians identified the sphere of stars with the Biblical
firmament In ancient near eastern cosmology, the firmament means a celestial barrier that separates the heavenly waters above from the Earth below. In biblical cosmology, the firmament ( ''rāqīaʿ'') is the vast solid dome created by God during the G ...
and sometimes posited an invisible layer of water above the firmament, to accord with
Genesis Genesis may refer to: Religion * Book of Genesis, the first book of the biblical scriptures of both Judaism and Christianity, describing the creation of the Earth and of humankind * Genesis creation narrative, the first several chapters of the Bo ...
. An outer sphere, inhabited by
angels An angel is a spiritual (without a physical body), heavenly, or supernatural being, usually humanoid with bird-like wings, often depicted as a messenger or intermediary between God (the transcendent) and humanity (the profane) in variou ...
, appeared in some accounts.
Edward Grant Edward Grant (April 6, 1926 – June 21, 2020) was an American historian of medieval science. He was named a distinguished professor in 1983. Other honors include the 1992 George Sarton Medal, for "a lifetime scholarly achievement" as an histor ...
, a historian of science, has provided evidence that medieval scholastic philosophers generally considered the celestial spheres to be solid in the sense of three-dimensional or continuous, but most did not consider them solid in the sense of hard. The consensus was that the celestial spheres were made of some kind of continuous fluid. Later in the century, the
mutakallim ''Ilm al-kalam'' or ''ilm al-lahut'', often shortened to ''kalam'', is the scholastic, speculative, or rational study of Islamic theology ('' aqida''). It can also be defined as the science that studies the fundamental doctrines of Islamic fai ...
Adud al-Din al-Iji (1281–1355) rejected the principle of uniform and circular motion, following the
Ash'ari Ash'arism (; ) is a school of theology in Sunni Islam named after Abu al-Hasan al-Ash'ari, a Shāfiʿī jurist, reformer (''mujaddid''), and scholastic theologian, in the 9th–10th century. It established an orthodox guideline, based on ...
doctrine of
atomism Atomism () is a natural philosophy proposing that the physical universe is composed of fundamental indivisible components known as atoms. References to the concept of atomism and its Atom, atoms appeared in both Ancient Greek philosophy, ancien ...
, which maintained that all physical effects were caused directly by God's will rather than by natural causes. He maintained that the celestial spheres were "imaginary things" and "more tenuous than a spider's web". His views were challenged by al-Jurjani (1339–1413), who maintained that even if the celestial spheres "do not have an external reality, yet they are things that are correctly imagined and correspond to what xistsin actuality". Medieval astronomers and philosophers developed diverse theories about the causes of the celestial spheres' motions. They attempted to explain the spheres' motions in terms of the materials of which they were thought to be made, external movers such as celestial intelligences, and internal movers such as motive souls or impressed forces. Most of these models were qualitative, although a few incorporated quantitative analyses that related speed, motive force and resistance. By the end of the Middle Ages, the common opinion in Europe was that celestial bodies were moved by external intelligences, identified with the
angel An angel is a spiritual (without a physical body), heavenly, or supernatural being, usually humanoid with bird-like wings, often depicted as a messenger or intermediary between God (the transcendent) and humanity (the profane) in variou ...
s of
revelation Revelation, or divine revelation, is the disclosing of some form of Religious views on truth, truth or Knowledge#Religion, knowledge through communication with a deity (god) or other supernatural entity or entities in the view of religion and t ...
. The outermost moving sphere, which moved with the daily motion affecting all subordinate spheres, was moved by an
unmoved mover The unmoved mover () or prime mover () is a concept advanced by Aristotle as a primary cause (or first uncaused cause) or " mover" of all the motion in the universe. As is implicit in the name, the moves other things, but is not itself moved by ...
, the
Prime Mover Prime mover may refer to: Philosophy *Unmoved mover, a concept in Aristotle's writings Engineering * Prime mover (engine or motor), a machine that converts various other forms of energy (chemical, electrical, fluid pressure/flow, etc.) into ener ...
, who was identified with God. Each of the lower spheres was moved by a subordinate spiritual mover (a replacement for Aristotle's multiple divine movers), called an intelligence.


Renaissance

Early in the sixteenth century
Nicolaus Copernicus Nicolaus Copernicus (19 February 1473 – 24 May 1543) was a Renaissance polymath who formulated a mathematical model, model of Celestial spheres#Renaissance, the universe that placed heliocentrism, the Sun rather than Earth at its cen ...
drastically reformed the model of astronomy by displacing the Earth from its central place in favour of the Sun, yet he called his great work ''
De revolutionibus orbium coelestium ''De revolutionibus orbium coelestium'' (English translation: ''On the Revolutions of the Heavenly Spheres'') is the seminal work on the heliocentric theory of the astronomer Nicolaus Copernicus (1473–1543) of the Polish Renaissance. The book ...
'' (''On the Revolutions of the Celestial Spheres''). Although Copernicus does not treat the physical nature of the spheres in detail, his few allusions make it clear that, like many of his predecessors, he accepted non-solid celestial spheres. Copernicus rejected the ninth and tenth spheres, placed the orb of the Moon around the Earth, and moved the Sun from its orb to the center of the
universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...
. The planetary orbs circled the center of the universe in the following order: Mercury, Venus, the great orb containing the Earth and the orb of the Moon, then the orbs of Mars, Jupiter, and Saturn. Finally he retained the eighth sphere of the
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s, which he held to be stationary. The English almanac maker,
Thomas Digges Thomas Digges (; c. 1546 – 24 August 1595) was an English mathematician and astronomer. He was the first to expound the Copernican system in English but discarded the notion of a fixed shell of immoveable stars to postulate infinitely many s ...
, delineated the spheres of the new cosmological system in his ''Perfit Description of the Caelestiall Orbes …'' (1576). Here he arranged the "orbes" in the new Copernican order, expanding one sphere to carry "the globe of mortalitye", the Earth, the four classical elements, and the Moon, and expanding the sphere of stars infinitely to encompass all the stars and also to serve as "the court of the Great God, the habitacle of the elect, and of the coelestiall angelles." In the sixteenth century, a number of philosophers, theologians, and astronomers—among them
Francesco Patrizi Franciscus Patricius (Croatian language, Croatian: ''Franjo Petriš'' or ''Frane Petrić''; Italian language, Italian: ''Francesco Patrizi''; 25 April 1529 – 6 February 1597) was a philosopher and scientist from the Republic of Venice, orig ...
, Andrea Cisalpino,
Peter Ramus Petrus Ramus (; Anglicized as Peter Ramus ; 1515 – 26 August 1572) was a French humanist, logician, and educational reformer. A Protestant convert, he was a victim of the St. Bartholomew's Day massacre. Early life He was born at the village ...
,
Robert Bellarmine Robert Bellarmine (; ; 4 October 1542 – 17 September 1621) was an Italian Jesuit and a cardinal of the Catholic Church. He was canonized a saint in 1930 and named Doctor of the Church, one of only 37. He was one of the most important figure ...
,
Giordano Bruno Giordano Bruno ( , ; ; born Filippo Bruno; January or February 1548 – 17 February 1600) was an Italian philosopher, poet, alchemist, astrologer, cosmological theorist, and esotericist. He is known for his cosmological theories, which concep ...
, Jerónimo Muñoz,
Michael Neander Michael Neander (originally Neumann) (April 3, 1529 – October 23, 1581) was a German teacher, mathematician, medical academic, and astronomer. He was born in Joachimsthal, Bohemia, and was educated at the University of Wittenberg, receiving h ...
, Jean Pena, and
Christoph Rothmann Christoph Rothmann (between 1550 and 1560 in Bernburg, Saxony-Anhalt – probably after 1600 in Bernburg) was a German mathematician and one of the few well-known astronomers of his time. His research contributed substantially to the fact that Ka ...
—abandoned the concept of celestial spheres. Rothmann argued from observations of the
comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...
of 1585 that the lack of observed
parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
indicated that the comet was beyond Saturn, while the absence of observed refraction indicated the celestial region was of the same material as air, hence there were no planetary spheres.
Tycho Brahe Tycho Brahe ( ; ; born Tyge Ottesen Brahe, ; 14 December 154624 October 1601), generally called Tycho for short, was a Danish astronomer of the Renaissance, known for his comprehensive and unprecedentedly accurate astronomical observations. He ...
's investigations of a series of comets from 1577 to 1585, aided by Rothmann's discussion of the comet of 1585 and
Michael Maestlin Michael Maestlin (; also ''Mästlin'', ''Möstlin'', or ''Moestlin''; 30 September 1550 – 26 October 1631) was a German astronomer and mathematician, best known as the mentor of Johannes Kepler. A student of Philipp Apian, Maestlin is recogniz ...
's tabulated distances of the comet of 1577, which passed through the planetary orbs, led Tycho to conclude that "the structure of the heavens was very fluid and simple." Tycho opposed his view to that of "very many modern philosophers" who divided the heavens into "various orbs made of hard and impervious matter." Edward Grant found relatively few believers in hard celestial spheres before Copernicus and concluded that the idea first became common sometime between the publication of Copernicus's ''De revolutionibus'' in 1542 and Tycho Brahe's publication of his cometary research in 1588. In his early ''Mysterium Cosmographicum'',
Johannes Kepler Johannes Kepler (27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, Natural philosophy, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best know ...
considered the distances of the planets and the consequent gaps required between the planetary spheres implied by the Copernican system, which had been noted by his former teacher, Michael Maestlin. Kepler's Platonic cosmology filled the large gaps with the five Platonic polyhedra, which accounted for the spheres' measured astronomical distance. In Kepler's mature celestial physics, the spheres were regarded as the purely geometric spatial regions containing each planetary orbit rather than as the rotating physical orbs of the earlier Aristotelian celestial physics. The eccentricity of each planet's orbit thereby defined the
radii In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is the line segment or ...
of the inner and outer limits of its celestial sphere and thus its thickness. In Kepler's celestial mechanics, the cause of planetary motion became the rotating Sun, itself rotated by its own motive soul. However, an immobile stellar sphere was a lasting remnant of physical celestial spheres in Kepler's cosmology.


Literary and visual expressions

In
Cicero Marcus Tullius Cicero ( ; ; 3 January 106 BC – 7 December 43 BC) was a Roman statesman, lawyer, scholar, philosopher, orator, writer and Academic skeptic, who tried to uphold optimate principles during the political crises tha ...
's ''
Dream of Scipio The ''Dream of Scipio'' (Latin: ''Somnium Scipionis''), written by Cicero, is the sixth book of ''De re publica'', and describes a (postulated fictional or real) dream vision of the Roman general Scipio Aemilianus, set two years before he overs ...
,'' the elder
Scipio Africanus Publius Cornelius Scipio Africanus (, , ; 236/235–) was a Roman general and statesman who was one of the main architects of Rome's victory against Ancient Carthage, Carthage in the Second Punic War. Often regarded as one of the greatest milit ...
describes an ascent through the celestial spheres, compared to which the Earth and the Roman Empire dwindle into insignificance. A commentary on the ''Dream of Scipio'' by the Roman writer
Macrobius Macrobius Ambrosius Theodosius, usually referred to as Macrobius (fl. AD 400), was a Roman provincial who lived during the early fifth century, during late antiquity, the period of time corresponding to the Later Roman Empire, and when Latin was ...
, which included a discussion of the various schools of thought on the order of the spheres, did much to spread the idea of the celestial spheres through the
Early Middle Ages The Early Middle Ages (or early medieval period), sometimes controversially referred to as the Dark Ages (historiography), Dark Ages, is typically regarded by historians as lasting from the late 5th to the 10th century. They marked the start o ...
. Some late medieval figures noted that the celestial spheres' physical order was inverse to their order on the spiritual plane, where God was at the center and the Earth at the periphery. Near the beginning of the fourteenth century
Dante Dante Alighieri (; most likely baptized Durante di Alighiero degli Alighieri; – September 14, 1321), widely known mononymously as Dante, was an Italian Italian poetry, poet, writer, and philosopher. His ''Divine Comedy'', originally called ...
, in the '' Paradiso'' of his ''
Divine Comedy The ''Divine Comedy'' (, ) is an Italian narrative poetry, narrative poem by Dante Alighieri, begun and completed around 1321, shortly before the author's death. It is widely considered the pre-eminent work in Italian literature and one of ...
'', described God as a light at the center of the cosmos. Here the poet ascends beyond physical existence to the
Empyrean In ancient European cosmologies inspired by Aristotle, the Empyrean heaven, Empyreal or simply the Empyrean, was the place in the highest heaven which was supposed to be occupied by the element of fire (or aether in Aristotle's natural philos ...
Heaven, where he comes face to face with God himself and is granted understanding of both divine and human nature. Later in the century, the illuminator of
Nicole Oresme Nicole Oresme (; ; 1 January 1325 – 11 July 1382), also known as Nicolas Oresme, Nicholas Oresme, or Nicolas d'Oresme, was a French philosopher of the later Middle Ages. He wrote influential works on economics, mathematics, physics, astrology, ...
's , a translation of and commentary on Aristotle's ''De caelo'' produced for Oresme's patron, King Charles V, employed the same motif. He drew the spheres in the conventional order, with the Moon closest to the Earth and the stars highest, but the spheres were concave upwards, centered on God, rather than concave downwards, centered on the Earth. Below this figure Oresme quotes the
Psalms The Book of Psalms ( , ; ; ; ; , in Islam also called Zabur, ), also known as the Psalter, is the first book of the third section of the Tanakh (Hebrew Bible) called ('Writings'), and a book of the Old Testament. The book is an anthology of B ...
that "The heavens declare the Glory of God and the firmament showeth his handiwork." The late-16th-century Portuguese epic ''
The Lusiads ''The'' is a grammatical article in English, denoting nouns that are already or about to be mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The ...
'' vividly portrays the celestial spheres as a "great machine of the universe" constructed by God.Luiz Vaz de Camões, ''The Lusiads'', translated by Landeg White. Oxford University Press, 2010. The explorer Vasco da Gama is shown the celestial spheres in the form of a mechanical model. Contrary to Cicero's representation, da Gama's tour of the spheres begins with the Empyrean, then descends inward toward Earth, culminating in a survey of the domains and divisions of earthly kingdoms, thus magnifying the importance of human deeds in the divine plan.


See also


Notes


Bibliography

* Aristotle ''Metaphysics'', in 'The Basic Works of Aristotle' Richard McKeon (Ed) The Modern Library, 2001 * Clagett, Marshall ''Science of Mechanics in the Middle Ages'' University of Wisconsin Press 1959 * Cohen, I.B. & Whitman, A. ''Principia'' University of California Press 1999 * Cohen & Smith (eds) ''The Cambridge Companion to Newton'' CUP 2002 * Copernicus, Nicolaus ''On the Revolutions of the Heavenly Spheres'', in ''Great Books of the Western World : 16 Ptolemy Copernicus Kepler'' Encyclopædia Britannica Inc 1952 * * Duhem, Pierre. "History of Physics." The Catholic Encyclopedia. Vol. 12. New York: Robert Appleton Company, 1911. 18 Jun. 2008 . * Duhem, Pierre. ''Le Système du Monde: Histoire des doctrines cosmologiques de Platon à Copernic,'' 10 vols., Paris: Hermann, 1959. * Duhem, Pierre. ''Medieval Cosmology: Theories of Infinity, Place, Time, Void, and the Plurality of Worlds'', excerpts from ''Le Système du Monde'', translated and edited by Roger Ariew, Chicago: University of Chicago Press, 1987 * * Eastwood, Bruce, "Astronomy in Christian Latin Europe c. 500 – c. 1150," ''Journal for the History of Astronomy,'' 28(1997): 235–258. * Eastwood, Bruce, ''Ordering the Heavens: Roman Astronomy and Cosmology in the Carolingian Renaissance,'' Leiden: Brill, 2007. . * Eastwood, Bruce and Gerd Graßhoff, ''Planetary Diagrams for Roman Astronomy in Medieval Europe, ca. 800–1500,'' ''Transactions of the American Philosophical Society,'' vol. 94, pt. 3, Philadelphia, 2004. * Field, J. V., ''Kepler's geometrical cosmology''. Chicago: Chicago University Press, 1988 * Golino, Carlo (ed.), ''Galileo Reappraised'', University of California Press 1966 * Grant, Edward, "Celestial Orbs in the Latin Middle Ages," ''Isis,'' 78(1987): 153–73; reprinted in Michael H. Shank, ed., ''The Scientific Enterprise in Antiquity and the Middle Ages,'' Chicago: Univ. of Chicago Pr., 2000. * Grant, Edward, ''Planets, Stars, and Orbs: The Medieval Cosmos, 1200–1687,'' Cambridge: Cambridge Univ. Pr., 1994. *Grant, Edward, ''The Foundations of Modern Science in the Middle Ages'', Cambridge: Cambridge Univ. Pr., 1996. * *Gingerich, Owen ''The Eye of Heaven'', American Institute of Physics 1993 * * Heath, Thomas, ''Aristarchus of Samos'' Oxford University Press/Sandpiper Books Ltd. 1913/97 * Jarrell, R.A., ''The contemporaries of Tycho Brahe'' in Taton & Wilson (eds)1989 * Koyré, Alexandre, ''Galileo Studies'' (translator Mepham) Harvester Press 1977 * * Kepler, Johannes, '' Epitome of Copernican Astronomy'' (Bks 4 & 5), published in ''Great Books of the Western World : 16 Ptolemy Copernicus Kepler'', Encyclopædia Britannica Inc. 1952 * Lewis, C. S., ''The Discarded Image: An Introduction to Medieval and Renaissance Literature'', Cambridge: Cambridge University Press 1964 * * Lindberg, David C. (ed.), ''Science in the Middle Ages'' Chicago: Univ. of Chicago Pr., 1978. * * Lloyd, G. E. R., ''Aristotle: The Growth and Structure of his Thought,'' pp. 133–153, Cambridge: Cambridge Univ. Pr., 1968. . * Lloyd, G. E. R., "Heavenly aberrations: Aristotle the amateur astronomer," pp. 160–183 in his ''Aristotelian Explorations,'' Cambridge: Cambridge Univ. Pr., 1996. . * Mach, Ernst, ''The Science of Mechanics'' Open Court 1960. * Maier, Annaliese, ''At the Threshold of Exact Science: Selected Writings of Annaliese Maier on Late Medieval Natural Philosophy'', edited by Steven Sargent, Philadelphia: University of Pennsylvania Press, 1982. * McCluskey, Stephen C., ''Astronomies and Cultures in Early Medieval Europe,'' Cambridge: Cambridge Univ. Pr., 1998. * Neugebauer, Otto, ''A History of Ancient Mathematical Astronomy,'' 3 vols., New York: Springer, 1975. * * Popper, Karl, ''The World of Parmenides'' Routledge 1996 * Rosen, Edward, ''Three Copernican Treatises'' Dover 1939/59. * Sambursky, S., ''The Physical World of Late Antiquity'' Routledge & Kegan Paul, 1962 * Schofield, C., ''The Tychonic and Semi-Tychonic World Systems'' in Taton & Wilson (eds) 1989 * Sorabji, Richard, ''Matter, Space and Motion'' London: Duckworth, 1988 * Sorabji, Richard, (ed.) ''Philoponus and the Rejection of Aristotelian Science'' London & Ithaca NY 1987 * Sorabji, Richard, ''The Philosophy of the Commentators, 200–600 AD: Volume 2 Physics'' Duckworth 2004 * * R. Taton & C. Wilson (eds.), ''The General History of Astronomy: Volume 2 Planetary astronomy from the Renaissance to the rise of astrophysics Part A Tycho Brahe to Newton'' Cambridge: Cambridge Univ. Pr., 1989 * Thoren, Victor E., "The Comet of 1577 and Tycho Brahe's System of the World," ''Archives Internationales d'Histoire des Sciences,'' 29 (1979): 53–67. * Thoren, Victor E., ''Tycho Brahe'' in Taton & Wilson 1989 *


External links


Working model and complete explanation of the Eudoxus's Spheres
*Dennis Duke

*Henry Mendell, Vignettes of Ancient Mathematics
M. Blundevile his exercises, p 282
– Depiction of celestial spheres in a 1613 book {{DEFAULTSORT:Celestial Spheres Ancient Greek astronomy Early scientific cosmologies Physical cosmology