Mediaeval drawing of the Ptolemaic system.

The Ptolemaic system was a model to explain the motions of the heavens in which the earth was the centre of the universe and all other celestial bodies revolved around it, espoused by Claudius Ptolemaeus in his work, the Almagest some time around the 2nd century, A.D., and accepted for over 1,000 years by the vast majority of Europeans to be the correct cosmological model. It may be also called the geocentric model. It was overthrown by the Copernican revolution after Galileo Galilei and Copernicus discovered that the planets orbited the sun. Image File history File links Ptolemaicsystem-small. ... Image File history File links Ptolemaicsystem-small. ... An abstract model (or conceptual model) is a theoretical construct that represents physical, biological or social processes, with a set of variables and a set of logical and quantitative relationships between them. ... This article is about the geographer and astronomer Ptolemy. ... Almagest is the Latin form of the Arabic name (al-kitabu-l-mijisti, i. ... The geocentric model The geocentric model (in Greek: geo = Earth and centron = center) of the universe is a disproven model which places the Earth at the center of the universe. ... Galileo Galilei Galileo Galileii (Pisa, February 15, 1564 – Arcetri, January 8, 1642), was an Italian physicist, astronomer, and philosopher who is closely associated with the scientific revolution. ... Nicolaus Copernicus (in Latin; Polish Mikołaj Kopernik, German Nikolaus Kopernikus - February 19, 1473 – May 24, 1543) was a Polish astronomer, mathematician and economist who developed a heliocentric (Sun-centered) theory of the solar system in a form detailed enough to make it scientifically useful. ...

The Almagest

An Epitome of the Almagest (Epitome in Ptolemaei Almagestum) was written between 1460 and 1463 by the Austrian astronomer Georg Peurbach and his famous pupil Johannes Regiomontanus at the suggestion of Cardinal Bessarion. It gave Europeans the first sophisticated understanding of Ptolemy's astronomy, and was studied by every competent astronomer of the 16th century. Events The first Portuguese navigators reach the coast of modern Sierra Leone. ... Events January 5 - Poet Francois Villon is banned from Paris Births January 17 - Frederick III, Elector of Saxony (died 1525) February 24 - Giovanni Pico della Mirandola, Italian philosopher (died 1494) October 20 - Alessandro Achillini, Italian philosopher (died 1512) Lorenzo di Pierfrancesco de Medici, Italian patron of the arts (died 1503... Georg Purbach (also Peuerbach, Peurbach, Purbach, Purbachius) (May 30, 1423 – April 8, 1461) was an Austrian astronomer and mathematician. ... Johannes Müller von Königsberg (June 6, 1436 – July 6, 1476), known by his Latin pseudonym Regiomontanus, was an important German mathematician, astronomer and astrologer. ... Johannes Bessarion, or Basilius (c. ... (15th century - 16th century - 17th century - more centuries) As a means of recording the passage of time, the 16th century was that century which lasted from 1501 to 1600. ...

Unlike earlier systems (such as 'the stars move because that is the will of the gods', or the model of concentric spheres), the Ptolemaic model explained all phenomena in the sky, while holding to Plato's dictum which states that all motions in the heavens can be explained with uniform, circular motion, and obeying Aristotelian physics. The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ... Concentric objects share the same center or origin. ... A sphere is a perfectly symmetrical geometrical object. ... A phenomenon (plural: phenomena) is an observable event, especially something special (literally something that can be seen from the Greek word phainomenon = observable). ... Plato Plato (Greek: Πλάτων, Plátōn) (c. ... 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 as precedent under the doctrine of stare decisis. ... Aristotle (Ancient Greek: Aristotelēs 384 BC – March 7, 322 BC) was an ancient Greek philosopher, student of Plato and teacher of Alexander the Great. ... A Superconductor demonstrating the Meissner Effect Physics (from the Greek, φυσικός (physikos), natural, and φύσις (physis), nature) is the science of the natural world dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. ...

Geocentricity

The basic elements of Ptolemaic astronomy, showing a planet on an epicycle with a deferent and an equant point.

According to the Ptolemaic model, the spherical Earth is at the center of the universe. All heavenly bodies are attached to crystal spheres which rotate around Earth. The Moon is on the innermost sphere, and touches the realm of Earth, thereby contaminating it, and causing the light and dark spots and the ability to go through phases. It is not perfect like the other heavenly bodies, which shine by their own light. The planets are actually attached to 2 spheres: one sphere which is centered on Earth (the deferent), and another sphere (the epicycle) embedded within the deferent. 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). (The earlier model based on concentric spheres explained retrograde motion, but did not explain the changes in brightness caused by the change in distance). 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 order of spheres from Earth outward is: Earth, Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, Stars. Image File history File links Ptolemaic_elements. ... Image File history File links Ptolemaic_elements. ... Equant is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of heavenly bodies. ... Earth is the third planet from the Sun, and the one we all live on. ... The deepest visible-light image of the cosmos. ... Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... A sphere is a perfectly symmetrical geometrical object. ... The Lachine Canal, in Montreal, is badly polluted Pollution is the release of harmful environmental contaminants, or the substances so released. ... Phase, from the Greek phasis, meaning appearance, has a number of related meanings in English. ... In the Ptolemaic system of astronomy, the epicycle (literally: on the cycle in Greek) was a geometric model to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets. ... In the Ptolemaic system of astronomy, the epicycle (literally: on the cycle in Greek) was a geometric model to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets. ... This article is about retrograde motion. ... Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... Atmospheric characteristics Atmospheric pressure trace Potassium 31. ... (*min temperature refers to cloud tops only) Atmospheric characteristics Atmospheric pressure 9. ... The Sun is the star at the center of our Solar system. ... Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ...

Problems with geocentricity

Unfortunately, the system still did not quite match observations. Sometimes the size of a planet's retrograde loop (most notably that of Mars) would be smaller, and sometimes larger. Ptolemy could not explain this even when he moved deferents off-center, for the change in loop size did not match with the change in speed. This prompted Ptolemy to come up with the idea of an equant. 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 at different points in its orbit. By using an equant, Ptolemy claimed to keep motion which was uniform and circular, but many people didn't like it because they didn't 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, using two sets of epicycles, revolving on a deferent, offset by an equant which was different for each retrograde planet (then known to be only Mars, Jupiter, and Saturn), but it predicted the beginnings and ends of retrograde motion far more accurately than either earlier Platonic spheres or early (and falsely perfect) Copernican systems. Observation is an activity of an intelligent living being, to sense and assimiliate the knowledge of a phenomenon in its framework of previous knowledge and ideas. ... For the Roman god, see Mars (mythology). ... Claudius Ptolemaeus, given contemporary German styling, in a 16th century engraved book frontispiece. ... Equant is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of heavenly bodies. ... In the Ptolemaic system of astronomy, the epicycle (literally: on the cycle in Greek) was a geometric model to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets. ... Claudius Ptolemaeus, given contemporary German styling, in a 16th century engraved book frontispiece. ... In the Ptolemaic system of astronomy, the epicycle (literally: on the cycle in Greek) was a geometric model to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets. ... In the Ptolemaic system of astronomy, the epicycle (literally: on the cycle in Greek) was a geometric model to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets. ... Equant is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of heavenly bodies. ... For the Roman god, see Mars (mythology). ... Adjective Jovian Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Adjective Saturnian Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... This article is about retrograde motion. ... In astronomy, heliocentrism is the theory that the Sun is at the center of the Universe and/or the Solar System. ...

Replacement with Copernican system

Though there were observations made (primarily by Galileo) which called into question some of the tenets of the Ptolemaic system (such as the fact that Jupiter also has moons), it was not until the discovery of the phases of Venus by Galileo in 1610 that the Ptolemaic system became untenable in any form. Under the Ptolemaic system, Venus can only be either between Earth and the Sun, or on the other side of the Sun (Ptolemy placed it inside the orbit of the Sun, after Mercury, but this was completely arbitrary; he could just as easily swapped Venus and Mercury and put them on the other side, or any combination of placements of Venus and Mercury, as long as they were always colinear with Earth and Sun). If that was the case, however, it would not appear to go through all phases, as was observed. If it was between the Earth and Sun, it would always appear mostly dark, since the light from the Sun would be falling mainly where we can't see it. On the other hand, if it was on the far side, we would only be able to see the lit side. Galileo saw it small and full, and later large and crescent. Galileo Galilei Galileo Galileii (Pisa, February 15, 1564 – Arcetri, January 8, 1642), was an Italian physicist, astronomer, and philosopher who is closely associated with the scientific revolution. ... Adjective Jovian Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... Adjective Venusian or (rarely) Cytherean (*min temperature refers to cloud tops only) Atmospheric characteristics Atmospheric pressure 9. ... // Events January 7 - Galileo Galilei discovers the Galilean moons of Jupiter. ... Adjective Venusian or (rarely) Cytherean (*min temperature refers to cloud tops only) Atmospheric characteristics Atmospheric pressure 9. ... Look up Mercury in Wiktionary, the free dictionary // Mercury may mean: Mercury (element), the chemical element also called quicksilver Mercury (planet), the nearest planet to the Sun in the solar system Mercury (mythology), messenger god from Roman mythology Mercury (astrology), a planet with astrological significance Other uses: Science Mercury (plant... A crescent is the shape produced when from a circular disk the disk of a circle which is a little smaller and tangent on the inside to the larger circle, is cut. ...

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 Tycho Brahe , born Tyge Ottesen Brahe (December 14, 1546 – October 24, 1601), was a Danish nobleman astronomer as well as an astrologer and alchemist. ... Tychonic system The Tychonic system (or Tychonian system) was an effort by Tycho Brahe to create a model of the solar system which would combine what he saw as the mathematical benefits of the Copernican system with the philosophical and physical benefits of the Ptolemaic system. ... In astronomy, heliocentrism is the theory that the Sun is at the center of the Universe and/or the Solar System. ...

References