Ptolemy (Claudius Ptolemaeus), fl. 2d cent. A.D., celebrated Greco-Egyptian mathematician, astronomer, and geographer. He made his observations in Alexandria and was the last great astronomer of ancient times. Although he discovered the irregularity in the moon's motion, known as evection, and made original observations regarding the motions of the planets, his place in the history of science is that of collator and expounder. He systematized and recorded the data and doctrines that were known to Alexandrian men of science. His works on astronomy and geography were the standard textbooks until the teachings of Copernicus Copernicus, Nicholas (kōpûr`nĭkəs), Pol. Mikotaj Kopérnik, 1473–1543, Polish astronomer.
..... Click the link for more information. came to be accepted. The mathematical and astronomical systems developed by the Greeks are contained in his 13-volume work, Almagest. With credit to Hipparchus Hipparchus, fl. 2d cent. B.C., Greek astronomer, b. Nicaea, Bithynia. He is the first systematic astronomer of whom there are records. He made his observations chiefly on the island of Rhodes.
..... Click the link for more information. as his chief authority, he presented in his famous book problems and explanations dealing with the known heavenly bodies and their relations to the earth. The Ptolemaic system Ptolemaic system (tŏl'əmā`ĭk), historically the most influential of the geocentric cosmological theories, i.e.
..... Click the link for more information. thus evolved represented the earth (a globe in form) as stationary in the center of the universe, with sun, moon, and stars revolving about it in circular orbits and at a uniform rate. From the center outward the elements were earth, water, air, fire, and ether. Beyond lay zones, or heavens, each an immense sphere. The planets were assumed to revolve in small circles, called epicycles, whose centers revolved around the earth in the vast circles, or deferents, of the spheres. (To account for the precession of the equinoxes and other phenomena, later astronomers found it necessary to add more epicycles and to make both epicycles and deferents eccentric.) The Almagest also contains other astronomical information, including a catalog of more than 1020 stars (giving their latitudes, longitudes, and magnitudes), as well as mathematical information, including a table of chords. Ptolemy's system of geography is founded upon the works of Marinus of Tyre; many errors stem from his underestimation of the earth's circumference. However, his system was in use until the 16th cent. His mathematical theories, most valuable in the field of trigonometry, are preserved in his Analemma and Planisphaerium. His writings, circulated in the original Greek and in Arabic and Latin translations, include also the Tetrabiblos, a study of astrology.

Bibliography

See tr. of his Geography by E. L. Stevenson (1932) and of his Almagest by R. C. Taliaferro (1952).

Ptolemy

Latin Claudius Ptolemaeus

(born c. AD 100—died c. AD 170) Greek astronomer and mathematician. He worked principally in Alexandria. It is often difficult to determine which findings in his great astronomical book, the Almagest, are Ptolemy's and which are Hipparchus's. The Sun, Moon, planets, and stars, he believed, were attached to crystalline spheres, centred on Earth, which turned to create the cycles of day and night, the lunar month, and so on. In order to explain retrograde motion of the planets, he refined a complex geometric model of cycles within cycles that was highly successful at predicting the planets' positions in the sky. The Earth-centred Ptolemaic system became dogmatically asserted in Western Christendom until the Sun-centred Copernican system replaced it. His Geography contained an estimate of the size of Earth, a description of its surface, and a list of places located by latitude and longitude. Ptolemy also dabbled in mechanics, optics, and music theory.

Ptolemy

Latin name Claudius Ptolemaeus. 2nd century ad, Greek astronomer, mathematician, and geographer. His Geography was the standard geographical textbook until the discoveries of the 15th century. His system of astronomy (see Ptolemaic system), as expounded in the Almagest, remained undisputed until the Copernican system was evolved

Ptolemy

(85–165) eminent Greek astronomer. [Gk. Hist.: Hall, 255]

See : Astronomy

Ptolemy

captain of Jericho invites Simon Maccabeus and his sons to a banquet and then slays them. [O.T.: I Maccabees, 16:16]

See : Treachery

Ptolemy (redirected from Claudius Ptolemaios)

Bibliography

Ptolemy

Ptolemy
(redirected from Claudius Ptolemaios)