Paragraph on “Why is Ptolemy important?” complete paragraph for Class 9, Class 10, Class 11 and Class 12

Why is Ptolemy important?

As we have said, the Greeks explored many new ideas about astronomy between 700 BC and AD 200. These ideas were finally written down by Claudius Ptolemais, better known as Ptolemy. Ptolemy lived and worked in Alexandria in the second century after Christ. Like the Greek astronomers that had preceded him, he believed that the Earth lay at the centre of the Universe and that the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn revolved around it, in that order, followed finally by a sphere that contained the fixed stars. Ancient astronomers believed that the stars did not move. Today we know that they do, but their movements are not very apparent because they are at such a vast distance from us.

These Greek astronomers believed that all the heavenly bodies revolved around the Earth in circular orbits. They were convinced they moved in circles because they held that the circle was the perfect geometric figure and that everything in the heavens must move in a perfect fashion. However, Ptolemy realized that it was not quite so simple. He had to make allowances for the fact that the planets do not move through the sky at the same speeds, and that at certain times they seem to stop and move backwards for a while, before returning to their forward motion. This could not be explained by orbits making circles.

Ptolemy’s theory contained a special device called an epicycle to overcome this problem. He believed that each planet moved in its own small circle or epicycle, and the centre of the epicycle moved round another circle called the deferent. The deferents moved around the Earth at uniform speeds. Even this complicated theory was not enough to explain all the motions of the planets and he had to suggest that the centre of the deferents was some way from the Earth ! As time went on this theory became more and more unsatisfactory, but nevertheless, it was accepted for nearly 1,400 years!