Figure of the heavenly bodies - An illustration of the Ptolemaic geocentric system by Portuguese cosmographer and cartographer Bartolomeu Velho, 1568 (Bibliotèque National, Paris)

In astronomy, the geocentric model of the universe is the theory that the Earth is at the center of the universe and the Sun and other objects go around it. Bartolomeu Velho (?-1568 was a sixteenth-century Portuguese mapmaker and cosmographer Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy The word theory has many distinct meanings in different fields of Knowledge, depending on their methodologies and the context of discussion. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Belief in this system was common in ancient Greece. The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca It was embraced by both Aristotle and Ptolemy, and most Greek philosophers assumed that the Sun, Moon, stars, and naked eye planets circle the Earth. Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. Claudius Ptolemaeus ( Greek: Klaúdios Ptolemaîos; after 83 &ndash ca Ancient Greek philosophy focused on the role of Reason and Inquiry. The Sun (Sol is the Star at the center of the Solar System. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth In Astronomy, the naked-eye planets are the five Planets of our Solar system that can be discerned with the Naked eye without much difficulty Similar ideas were held in ancient China. Astronomy in China has a very long history Oracle bones from the Shang Dynasty ( 2nd millennium BC) record eclipses and novae ^[1]

Two common observations were believed to support the idea that the Earth is in the center of the Universe. The first is that the stars (including the Sun and planets) appear to revolve around the Earth each day, with the stars circling around the pole and those stars nearer the equator rising and setting each day and circling back to their rising point. ^[2] The second is the common sense perception that the Earth is solid and stable; it is not moving but is at rest.

The geocentric model was usually combined with a spherical Earth by ancient Greek and medieval philosophers. The concept of a spherical Earth dates back to around the 6th century BC in ancient Greek philosophy and possibly ancient Indian philosophy. It is not the same as the older flat Earth model implied in some mythology. The idea of a flat Earth is the idea that the surface of the Earth is flat (a plane) rather than the view that it is a very close approximation of The word mythology (from the Greek grc μυθολογία mythología, meaning "a story-telling a legendary lore" The ancient Greeks also believed that the motions of the planets were circular and not elliptical, a view that was not challenged in western culture before the 17th century.

The geocentric model held sway into the early modern age; from the late 16th century onward it was gradually replaced by the heliocentric model of Copernicus, Galileo and Kepler. The early modern period is a term initially used by historians to refer mainly to the period roughly from 1500 to 1800 in Western Europe ( Early modern Europe) In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher Johannes Kepler (ˈkɛplɚ ( December 27 1571 &ndash November 15 1630) was a German Mathematician, Astronomer Today, geocentric cosmology survives as a literary element within alternate history science fiction. Alternate history or alternative history is a subgenre of Speculative fiction (or Science fiction) and Historical fiction

Classical Greece

The geocentric model entered Greek astronomy and philosophy at an early point; it can be found in Pre-socratic philosophy. Greek astronomy is the Astronomy of those who wrote in the Greek language in Classical antiquity. The Pre-Socratic Greek philosophers were active before Socrates or contemporaneously but expounding knowledge developed earlier In the 6th century BC, Anaximander proposed a cosmology with the Earth shaped like a section of a pillar (a cylinder), held aloft at the center of everything. Anaximander ( Ancient Greek:) (c 610 BC–c 546 BC was a Pre-Socratic Greek philosopher who lived in Miletus The Sun, Moon, and planets were holes in invisible wheels surrounding the Earth; through the holes, humans could see concealed fire. About the same time, the Pythagoreans thought that the Earth was a sphere (in accordance with observations of eclipses), but not at the center; they believed that it was in motion around an unseen fire. Pythagoreanism is a term used for the Esoteric and metaphysical beliefs held by Pythagoras and his followers the Pythagoreans who were much influenced Later these views were combined, so most educated Greeks from the 4th century BC on thought that the Earth was a sphere at the center of the universe.

In the 5th century BC, two influential Greek philosophers wrote works based on the geocentric model. These were Plato and his student Aristotle. Biography Early life Birth and family Plato was born in Athens Greece Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. According to Plato, the Earth was a sphere, stationary at the center of the universe. The stars and planets were carried around the Earth on spheres or circles, arranged in the order (outwards from the center): Moon, Sun, Venus, Mercury, Mars, Jupiter, Saturn, fixed stars. The celestial spheres or celestial orbs were the fundamental celestial entities of the cosmological celestial mechanics first invented by Eudoxus, and developed by Aristotle In the "Myth of Er," a section of the Republic, Plato describes the cosmos as the Spindle of Necessity, attended by the Sirens and turned by the three Fates. The Myth of Er is an eschatological legend that concludes Plato 's dialogue known as "The Republic" (10 The Republic ( Greek: / Politeía, meaning "political system" Latin: Res Publica, meaning "public business" or The Myth of Er is an eschatological legend that concludes Plato 's dialogue known as "The Republic" (10 In Greek mythology, the Sirens ( Greek singular Seirēn; Greek plural Seirēnes) were three dangerous bird-women Eudoxus of Cnidus, who worked with Plato, developed a less mythical, more mathematical explanation of the planets' motion based on Plato's dictum stating that all phenomena in the heavens can be explained with uniform circular motion. Eudoxus of Cnidus ( Greek Εὔδοξος ὁ Κνίδιος (410 or 408 BC &ndash 355 or 347 BC was a Greek Astronomer, Mathematician In common law legal terminology a dictum (plural dicta) is any statement that forms a part of the Judgment of a court in particular a court whose decisions have value A phenomenon (from Greek φαινόμενoν, pl φαινόμενα - phenomena) is any observable occurrence Aristotle elaborated on Eudoxus' system. In the fully developed Aristotelian system, the spherical Earth is at the center of the universe. All heavenly bodies are attached to 56 concentric spheres which rotate around the Earth . (The number is so high because several transparent spheres are needed for each planet. ) The Moon is on the innermost sphere. Thus it touches the realm of Earth, which contaminates it, causing the dark spots (macula) and the ability to go through lunar phases. The macula or macula lutea (from Latin macula, "spot" + lutea, "yellow" is an oval Yellow spot near the center Lunar phase (or Moon phase refers to the appearance of the illuminated portion of the Moon as seen by an observer usually on Earth It is not perfect like the other heavenly bodies, which shine by their own light.

Adherence to the geocentric model stemmed largely from several important observations. First of all, if the Earth did move, then one ought to be able to observe the shifting of the fixed stars due to parallax. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between In short, the shapes of the constellations should change considerably over the course of a year, or else the stars are so much further away than the Sun and the planets that this motion would be undetectable. In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture Stellar parallax was not detected until the 19th century as the distances from the Earth to the stars made the effect extremely subtle, so the Greeks chose the simpler of the two explanations (either the Earth is not moving and so no effect exists, or the stars are so far away the effect was undetectable). The lack of any observable parallax was considered a fatal flaw of any non-geocentric theory.

Another important influence observation was that Venus stays about the same brightness most of the time, implying that it is usually about the same distance from Earth, which is more consistent with geocentrism than heliocentrism. In reality, that is because the loss of light caused by its phases compensates for the increase in apparent size caused by its varying distance from Earth. Other objections included the idea, put forward by Aristotle, that the natural state of heavy objects like the Earth was at rest, and that some force was required to move them. It was also believed by some that the Earth's rotation on its axis would cause the air and objects in it (such as birds or clouds) to be left behind.

A major flaw in the Eudoxan and Aristotelian models based on concentric spheres was that they could not explain the changes in brightness of the planets caused by a change in distance.

Claudius Ptolemy

Although the basic tenets of Greek geocentrism were established by the time of Aristotle, the details of his system did not become standard. This honor was reserved for the Ptolemaic system, espoused by the Hellenistic astronomer Claudius Ptolemaeus in the 2nd century AD. Hellenization (or Hellenisation) is a term used to describe the spread of Greek culture. Claudius Ptolemaeus ( Greek: Klaúdios Ptolemaîos; after 83 &ndash ca His main astronomical book, the Almagest, was the culmination of centuries of work by Hellenic, Hellenistic and Babylonian astronomers; it was accepted for over a millennium as the correct cosmological model by European and Islamic astronomers. Almagest is the Latin form of the Arabic name ( الكتاب المجسطي, al-kitabu-l-mijisti, i The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca This article focuses on the cultural aspects of the Hellenistic age for the historical aspects see Hellenistic period. Babylonian astronomy refers to the astronomical theories and methods that were developed in ancient Mesopotamia, the "land between the rivers" Tigris Because of its influence, the Ptolemaic system is sometimes considered identical with the geocentric model.

Ptolemy argued that the Earth was in the center of the universe from the simple observation that half the stars were above the horizon and half were below the horizon at any time, and the assumption that the stars were all at some modest distance from the center of the universe. If the Earth were substantially displaced from the center, this division into visible and invisible stars would not be equal. ^[3]

The basic elements of Ptolemaic astronomy, showing a planet on an epicycle with an eccentric deferent and an equant point. In the Ptolemaic system of Astronomy, the epicycle (literally on the circle in Greek) was a geometric model used to explain the variations in Equant (or Punctum aequans) is a Mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed

Ptolemaic system

In the Ptolemaic system, each planet is moved by five or more spheres: one sphere is its deferent. In the Ptolemaic system of Astronomy, the epicycle (literally on the circle in Greek) was a geometric model used to explain the variations in The deferent was a circle centered around a point halfway between the equant and the earth. Equant (or Punctum aequans) is a Mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed Another sphere is the epicycle which is embedded in the deferent. The planet is embedded in the epicycle sphere. The deferent rotates around the Earth while the epicycle rotates within the deferent, causing the planet to move closer to and farther from Earth at different points in its orbit, and even to slow down, stop, and move backward (in retrograde motion). Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. The epicycles of Venus and Mercury are always centered on a line between Earth and the Sun (Mercury being closer to Earth), which explains why they are always near it in the sky. The Ptolemaic order of spheres from Earth outward is:

1. Moon
2. Mercury
3. Venus
4. Sun
5. Mars
6. Jupiter
7. Saturn
8. Fixed Stars

The deferent-and-epicycle model had been used by Greek astronomers for centuries, as had the idea of the eccentric (a deferent which is slightly off-center from the Earth). In the illustration, the center of the deferent is not the Earth but X, making it eccentric (from the Latin ex- or e- meaning "from," and centrum meaning "center"). Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. Unfortunately, the system that was available in Ptolemy's time did not quite match observations, even though it was considerably improved over Aristotle's system. Observation is either an activity of a living being (such as a Human) which senses and assimilates the Knowledge of a Phenomenon, or the recording of data Sometimes the size of a planet's retrograde loop (most notably that of Mars) would be smaller, and sometimes larger. This prompted him to come up with the idea of an equant. Equant (or Punctum aequans) is a Mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed The equant was a point near the center of a planet's orbit which, if you were to stand there and watch, the center of the planet's epicycle would always appear to move at the same speed. Therefore, the planet actually moved at different speeds when the epicycle was at different points on its deferent. By using an equant, Ptolemy claimed to keep motion which was uniform and circular, but many people did not like it because they did not think it was true to Plato's dictum of "uniform circular motion. " The resultant system which eventually came to be widely accepted in the west was an unwieldy one to modern eyes; each planet required an epicycle revolving on a deferent, offset by an equant which was different for each planet. But it predicted various celestial motions, including the beginnings and ends of retrograde motion, fairly well at the time it was developed.

This drawing from an Icelandic manuscript dated around 1750 illustrates the geocentric model. Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland (

Geocentrism and rival systems

Not all Greeks agreed with the geocentric model. The Pythagorean system has already been mentioned; some Pythagoreans believed the Earth to be one of several planets going around a central fire. Hicetas and Ecphantus, two Pythagoreans of the 5th century BC, and Heraclides Ponticus in the 4th century BC, believed that the Earth rotated on its axis but remained at the center of the universe. Hicetas (ca 400 BC &ndash ca 335 BC was a Greek Philosopher of the Pythagorean School. Ecphantus ( Ecphantos) is a shadowy Greek Pre-Socratic philosopher "Heraclides" redirects here The former Butterfly Genus of the same name is now included in Papilio. Such a system still qualifies as geocentric. It was revived in the Middle Ages by Jean Buridan. Jean Buridan (in Latin, Johannes Buridanus; ca 1295 &ndash 1358 was a French Priest who sowed the seeds of the Copernican revolution Heraclides Ponticus is also sometimes said to have proposed that both Venus and Mercury went around the Sun rather than Earth, but the evidence for this claim is not clear. Martianus Capella definitely put Mercury and Venus on epicycles around the Sun. "Martianus" redirects here For the beetle Genus, see Martianus (beetle.

Aristarchus of Samos was the most radical. He wrote a work, which has not survived, on heliocentrism, saying that the Sun was at the center of the universe, while the Earth and other planets revolved around it. In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System. His theory was not popular, and he had only one known follower, Seleucus of Seleucia. Seleucus (or Seleukos) of Seleucia (born c 190 BC fl 150s BC was a Babylonian astronomer from the Seleucia

Copernican system

In 1543 the geocentric system met its first serious challenge with the publication of Copernicus's De revolutionibus orbium coelestium, which posited that the Earth and the other planets instead revolved around the Sun. De revolutionibus orbium coelestium ( On the Revolutions of the Heavenly Spheres) first printed in 1543 in Nuremberg, is the seminal work on The geocentric system was still held for many years afterwards, as at the time the Copernican system did not offer better predictions than the geocentric system, and it posed problems for both natural philosophy and scripture. For the current in the 19th century German idealism see Naturphilosophie Natural philosophy or the philosophy of nature (from

With the invention of the telescope in 1609, observations made primarily by Galileo Galilei (such as that Jupiter has moons) called into question some of the tenets of geocentrism but did not seriously threaten it. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher

Phases of Venus

In December 1610, Galileo Galilei used his telescope to observe that Venus showed all phases, just like the Moon. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University The phases of Venus vary from a thin crescent to full phase in 584 days Lunar phase (or Moon phase refers to the appearance of the illuminated portion of the Moon as seen by an observer usually on Earth This observation was incompatible with the Ptolemaic system, but was a natural consequence of the heliocentric system.

Ptolemy placed Venus's deferent and epicycle entirely inside the sphere of the Sun (between the Sun and Mercury), but this was arbitrary; he could just as easily have swapped Venus and Mercury and put them on the other side of the Sun, or made any other arrangement of Venus and Mercury, as long as they were always near a line running from the Earth through the Sun. In the Ptolemaic system of Astronomy, the epicycle (literally on the circle in Greek) was a geometric model used to explain the variations in In the Ptolemaic system of Astronomy, the epicycle (literally on the circle in Greek) was a geometric model used to explain the variations in In this case, if the Sun is the source of all the light, under the Ptolemaic system:

If Venus is between Earth and the Sun, the phase of Venus must always be crescent or all dark. For things named Crescent see Crescent (disambiguation. In art and symbolism a crescent is generally the shape produced when a

If Venus is beyond the Sun, the phase of Venus must always be gibbous or full. Lunar phase (or Moon phase refers to the appearance of the illuminated portion of the Moon as seen by an observer usually on Earth

But Galileo saw Venus at first small and full, and later large and crescent.

Astronomers of this time period saw the result of this being unsalvageable for a Ptolemaic cosmology, if the results were accepted as true. As a result, later 17th century competition between astronomical cosmologies focused on variations of Tycho Brahe's Tychonic system (in which the Earth was still at the center of the universe, and around it revolved the Sun, but all other planets revolved around the Sun in one massive set of epicycles), or variations on the Copernican system. Tycho Brahe, born Tyge Ottesen Brahe ( December 14 1546 &ndash October 24 1601) was a Danish nobleman The Tychonic system (or Tychonian system) was a model of the Solar system published by Tycho Brahe in the late 16th century which combined what he saw as

Gravitation

Johannes Kepler, after analysing Tycho Brahe's observations, constructed his three laws in 1609 and 1619, based on a heliocentric view where the planets moves in elliptical paths. Johannes Kepler (ˈkɛplɚ ( December 27 1571 &ndash November 15 1630) was a German Mathematician, Astronomer Tycho Brahe, born Tyge Ottesen Brahe ( December 14 1546 &ndash October 24 1601) was a Danish nobleman In Astronomy, Kepler's Laws of Planetary Motion are three mathematical laws that describe the motion of Planets in the Solar System. In Mathematics, an ellipse (from the Greek ἔλλειψις literally absence) is a Conic section, the locus of points in a Using these laws, he was the first astronomer to successfully predict a transit of Venus (for the year 1631).

In 1687, Isaac Newton devised his law of universal gravitation, which introduced gravitation as the force that both kept the Earth and planets moving through the heavens and also kept the air from flying away, allowing scientists to quickly construct a plausible heliocentric model for the solar system. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass

In 1838, astronomer Friedrich Wilhelm Bessel successfully measured the parallax of the star 61 Cygni, disproving Ptolemy's assertion that parallax motion did not exist. Friedrich Wilhelm Bessel (22 July 1784 &ndash 17 March 1846 was a German Mathematician, Astronomer, and systematizer of the Bessel functions Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between Not be confused with 16 Cygni, a more distant system containing two G-type stars harboring the Gas giant planet 16 Cygni Bb.

A geocentric frame is useful for many everyday activities and most laboratory experiments, but is a less felicitous choice for solar-system mechanics and space travel. While a heliocentric frame is most useful in those cases, galactic and extra-galactic astronomy is easier if the sun is treated as neither stationary nor the center of the universe, but rotating around the center of our galaxy. In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System.

Geocentrism today

Main article: Modern geocentrism

Individuals of some religions interpret their scriptures literally as stating that the Earth is the physical center of the universe. Modern geocentrism is a belief currently held by certain groups such as the Association for Biblical Astronomy which publishes the Biblical Astronomer and hosts a website, This requires the Sun to revolve around the Earth instead of the other way around because if the Earth were moving it could not continuously be in the center of the universe. This is known as modern geocentrism. Astrologers, while they may not believe in geocentrism as a principle, still employ the geocentric model in their calculations. Planets in astrology have a meaning different from the modern astronomical understanding of what a planet is.

The contemporary Association for Biblical Astronomy, led by physicist Dr. Gerardus Bouw, holds to a modified version of the model of Tycho Brahe, which they call geocentricity.

A study done by Dr. Jon D. Miller of Northwestern University, an expert in the public understanding of science and technology^[4], found that today one adult American in five thinks the Sun revolves around the Earth. ^[5]

Planetariums

The geocentric (Ptolemaic) model of the solar system is still of interest to planetarium makers, as, for technical reasons, a Ptolemaic-type motion for the planet light apparatus has some advantages over a Copernican-type motion. A planetarium is a Theatre built primarily for presenting educational and entertaining shows about Astronomy and the night sky or for training in Celestial navigation The celestial sphere, used for teaching purposes and sometimes for navigation, is also still based on a geocentric system. In Astronomy and Navigation, the celestial sphere is an imaginary rotating Sphere of "gigantic Radius "

Science fiction

Alternate history science fiction has produced some literature of interest on the proposition that some alternate universes and Earths might indeed have laws of physics and cosmologies that are Ptolemaic and Aristotelian in design. Alternate history or alternative history is a subgenre of Speculative fiction (or Science fiction) and Historical fiction This subcategory began with Philip Jose Farmer's short story, Sail On! Sail On! (1952), where Columbus has access to radio technology, and where his Spanish-financed exploratory and trade fleet sail off the edge of the (flat) world in his geocentric alternate universe in 1492, instead of discovering North America and South America. Philip José Farmer (born January 26 1918) is an American Author, principally known for his Science fiction and fantasy The short story is a literary genre of Fictional Prose Narrative that tends to be more concise and to the point than longer works of fiction such Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Spain () or the Kingdom of Spain (Reino de España is a country located mostly in southwestern Europe on the Iberian Peninsula. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a

Richard Garfinkle's Celestial Matters (1996) is set in a more elaborated geocentric cosmos, where Earth is divided by two contending factions, the Classical Greece-dominated Delian League and the (Chinese) Middle Kingdom, both of which are capable of flight within an alternate universe based on Ptolemaic astronomy, Aristotle's physics and Taoist thought. Richard Garfinkle (fl 1990s is an American writer of Science fiction. Celestial Matters is a science fiction novel set in an alternate universe with different laws of physics written by Richard Garfinkle and published by In the context of the art architecture and culture of Ancient Greece, the classical period corresponds to most of the 5th and 4th centuries The Delian League was an association of approximately 150 5th-century BC Greek City-states under the leadership of Athens, whose purpose was to continue In Astronomy, the geocentric model of the Universe is the superseded theory that the Earth is the center of the universe and other Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. Taoism (pronounced /ˈdaʊɪzəm/ or /ˈtaʊɪzəm/ also spelled '''Daoism''') refers to a variety of related Philosophical and Religious traditions Unfortunately, both superpowers have been fighting a thousand-year war since the time of Alexander the Great. Alexander the Great ( or, Mégas Aléxandros; July 20 356 BC June 10 or June 11 323 BC also known as Alexander III of Macedon (el Ἀλέξανδρος Γ'

Notes

References

• Crowe, Michael J. (1990). Theories of the World from Antiquity to the Copernican Revolution. Mineola, NY: Dover Publications, Inc. ISBN 0-486-26173-5.  
• Dreyer, J. L. E.. John Louis Emil Dreyer ( February 13 1852 &ndash September 14 1926) was a Danish - Irish Astronomer. A History of Astronomy from Thales to Kepler. 2nd edition. New York: Dover Publications, 1953.
• Evans, James. The History and Practice of Ancient Astronomy. New York: Oxford University Press, 1998.
• Heath, Thomas. Sir Thomas Little Heath ( October 5, 1861 &ndash March 16, 1940) was a British civil servant Mathematician, classical Aristarchus of Samos. Oxford: Clarendon Press, 1913
• Hoyle, Fred, Nicolaus Copernicus, 1973. Sir Fred Hoyle FRS ( 24 June, 1915  &ndash 20 August, 2001) was an English Astronomer primarily
• Koestler, Arthur The Sleepwalkers: A History of Man's Changing Vision of the Universe, 1959, Penguin Books, 1986 edition: ISBN 0-14-055212-X, 1990 reprint: ISBN 0-14-019246-8
• Kuhn, Thomas S. The Copernican Revolution. Arthur Koestler CBE ( September 5, 1905, Budapest &ndash March 3, 1983, London) was a Thomas Samuel Kuhn (surname ˈkuːn July 18, 1922  &ndash June 17, 1996) was an American intellectual who wrote extensively Cambridge: Harvard Univ. Pr. , 1957. ISBN 0-674-17103-9
• Walker, Christopher, ed. Astronomy before the telescope. London: British Museum Press, 1996. ISBN 0-7141-1746-3

See also

• Celestial spheres
• Firmament
• Heliocentrism

External links

• Geocentric Perspective animation of the Solar System in 150AD
• Another demonstration of the complexity of observed orbits when assuming a geocentric model of the solar system
• Official Geocentricity Website, Association for Biblical Astronomy
• The World & Universe
• Ptolemy's explaination for retrograde motion
• Ptolemy’s system of astronomy