Ptolemy, Latin in full Claudius Ptolemaeus (born c. 100 ce—died c. 170), an Egyptian astronomer, mathematician, and geographer of Greek descent who flourished in Alexandria during the 2nd century ce.
In several fields his writings represent the culminating achievement of Greco-Roman science, particularly his geocentric (Earth-centred) model of the universe now known as the Ptolemaic system.
Ptolemy’s reputation came along with his astronomical works.
He recorded over 1000 stars, of which 300 were newly found.
Also, he was responsible for the formation of the first practical theory of refraction of light. He had discussed about the dimensions of the planets with much precision.
The ‘Almagest’, an astronomical treatise by Ptolemy is a complete text on the ancient view of astronomy.
Ptolemy’s inspiration for the book was the astronomical observations recorded by his predecessors.
These observations were already 800 years old when Ptolemy sat to write his book. In this he revealed his vision of the universe by studying the observations of his ancestors.
The ‘Almagest’ was considered the Gospel of astronomy by his successors for many centuries throughout medieval Europe.
The ancient Greeks were of the opinion that the path of the planets was completely spherical which was disproven by later discoveries which established that the orbits are elliptical.
Even Ptolemy held this belief. In his manual Ptolemy clearly followed the steps of Aristotle who propounded that the planets moved in perfect circles in a continuous and uniform motion.
Ptolemy’s observation described the earth as a spherical object which he argued remains suspended freely in the center of the universe.
The stars were fixed bodies attached to a solid exterior of the universe which lay beyond the orbit of Saturn.
Most of these studies were based on Aristotle’s philosophy; however, by determining the motions of each of the planets in a detailed manner, Ptolemy offered an original contribution in the field of astronomy.
How much of the Almagest is original is difficult to determine because almost all of the preceding technical astronomical literature is now lost.
Ptolemy credited Hipparchus (mid-2nd century bce) with essential elements of his solar theory, as well as parts of his lunar theory, while denying that Hipparchus constructed planetary models.
Ptolemy made only a few vague and disparaging remarks regarding theoretical work over the intervening three centuries; yet the study of the planets undoubtedly made great strides during that interval.
Moreover, Ptolemy’s veracity, especially as an observer, has been controversial since the time of the astronomer Tycho Brahe (1546–1601).
Brahe pointed out that solar observations Ptolemy claimed to have made in 141 are definitely not genuine, and there are strong arguments for doubting that Ptolemy independently observed the more than 1,000 stars listed in his star catalog.
What is not disputed, however, is the mastery of mathematical analysis that Ptolemy exhibited.
Ptolemy’s most important geographical innovation was to record longitudes and latitudes in degrees for roughly 8,000 locations on his world map, making it possible to make an exact duplicate of his map.
Hence, we possess a clear and detailed image of the inhabited world as it was known to a resident of the Roman Empire at its height—a world that extended from the Shetland Islands in the north to the sources of the Nile in the south, from the Canary Islands in the west to China and Southeast Asia in the east.
Ptolemy’s map is seriously distorted in size and orientation compared to modern maps, a reflection of the incomplete and inaccurate descriptions of road systems and trade routes at his disposal.