Knowra Deferent and epicycle Deferent and epicycle A geocentric model in which a planet moves on an epicycle whose center travels along a larger circle called the deferent. The construction reproduced complex planetary motions using combinations of circular motion.
Ptolemaic system : A geocentric astronomical system that describes celestial motions through combinations of circles. The deferent and epicycle form the system’s basic machinery for modeling planets.
Hipparchus : A Greek astronomer of the second century BCE known for mathematical astronomy and a star catalogue. His work helped establish geometric models of planetary motion later developed by Ptolemy.
Ptolemaic model of the Solar System : A geocentric arrangement of the Sun, Moon, planets, and stars described through nested celestial motions. Its planetary paths used deferents and epicycles to calculate changing positions from Earth.
Heliocentrism : The astronomical view that the planets, including Earth, orbit the Sun. It explains apparent planetary retrograde motion through Earth’s and other planets’ relative orbital motion.
Medieval Latin translations of Greek texts : The translation of Greek scholarly works into Latin, especially during the Middle Ages. Latin versions of Ptolemy’s astronomy helped transmit epicycle-based methods across medieval Europe.
Equant : A point offset from a circle’s center from which uniform angular motion is measured in Ptolemaic astronomy. Ptolemy added this device to improve planetary predictions beyond the deferent and epicycle alone.
Apollonius of Perga : A Greek mathematician whose work on conic sections also addressed geometrical models of celestial motion. Ancient tradition associated him with the development of epicyclic methods.
Planetary tables : Numerical tables used to calculate the positions and motions of celestial bodies. Epicycle parameters could be turned into tables for predicting planetary locations.
Keplerian orbit : An orbit following Kepler’s laws, with a planet moving on an ellipse around a focus. Elliptical orbits replaced combinations of circles as a simpler account of planetary paths.
Islamic Golden Age : A period of flourishing scholarship and cultural production across parts of the Islamic world, chiefly from the eighth to thirteenth centuries. Its astronomers inherited, tested, and revised the mathematical astronomy built around Ptolemaic circles.
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