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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 ...
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 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 ...
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. [2] When scholars applied Ptolemy's epicycles, they presumed that each planetary sphere was exactly thick enough to accommodate them ...
In Almagest V, 11, Ptolemy writes: . Now Hipparchus made such an examination principally from the sun. Since from other properties of the sun and moon (of which a study will be made below) it follows that if the distance of one of the two luminaries is given, the distance of the other is also given, he tries by conjecturing the distance of the sun to demonstrate the distance of the moon.
Astronomy in the Indian subcontinent dates back to the period of Indus Valley Civilisation during 3rd millennium BC, when it was used to create calendars. [28] As the Indus Valley civilization did not leave behind written documents, the oldest extant Indian astronomical text is the Vedanga Jyotisha, dating from the Vedic period. [29]
Ptolemy I and other early rulers of the dynasty were not married to their relatives, the childless marriage of siblings Ptolemy II and Arsinoe II [22] being an exception. The first child-producing incestuous marriage in the Ptolemaic dynasty was that of Ptolemy IV and Arsinoe III , who were succeeded as co-pharaohs by their son Ptolemy V , born ...
The triquetrum (derived from the Latin tri-["three"] and quetrum ["cornered"]) was the medieval name for an ancient astronomical instrument first described by Ptolemy (c. 90 – c. 168) in the Almagest (V. 12). Also known as Parallactic Rulers, it was used for determining altitudes of heavenly bodies.