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For the Moon, Ptolemy began with Hipparchus' epicycle-on-deferent, then added a device that historians of astronomy refer to as a "crank mechanism": [28] he succeeded in creating models for the other planets, where Hipparchus had failed, by introducing a third device called the equant. Ptolemy wrote the Syntaxis as a textbook of mathematical ...
The angular rate at which the epicycle traveled was not constant unless he measured it from another point which is now called the equant (Ptolemy did not give it a name). It was the angular rate at which the deferent moved around the point midway between the equant and the Earth (the eccentric) that was constant; the epicycle center swept out ...
The basic elements of Ptolemaic astronomy, showing a planet on an epicycle (smaller dashed circle), a deferent (larger dashed circle), the eccentric (×) and an equant (•). Equant (or punctum aequans) is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of the planets. The equant is ...
Ptolemy attempted to resolve the Planetary motion dilemma in which the observations were not consistent with the perfect circular orbits of the bodies. Ptolemy adopted the Apollonius' epicycles as solution. [47] Ptolemy emphasised that the epicycle motion does not apply to the Sun. His main contribution to the model was the equant points. He ...
Ptolemy states that having dealt with the former subject (astronomy) in its own treatise, he "shall now give an account of the second and less self-sufficient method in a properly philosophical way, so that one whose aim is the truth might never compare its perceptions with the sureness of the first". [27]
The Canon of Kings was a dated list of kings used by ancient astronomers as a convenient means to date astronomical phenomena, such as eclipses.For a period, the Canon was preserved by the astronomer Claudius Ptolemy, and is thus known sometimes as Ptolemy's Canon.
The first astronomer known to have continued Hipparchus's work on precession is Ptolemy in the second century AD. Ptolemy measured the longitudes of Regulus, Spica, and other bright stars with a variation of Hipparchus's lunar method that did not require eclipses. Before sunset, he measured the longitudinal arc separating the Moon from the Sun.
In classical, medieval, and Renaissance astronomy, the Primum Mobile (Latin: "first movable") was the outermost moving sphere in the geocentric model of the universe. [ 1 ] The concept was introduced by Ptolemy to account for the apparent daily motion of the heavens around the Earth, producing the east-to-west rising and setting of the sun and ...