Ptolemy has wrote many books in his time which are explaining the observations of Ptolemy. The names of three prominent books of Ptolemy are "Handy Tables", "Geography" and "Almagest". The work mentioned in book named "Almagest" is considered as the earliest work of Ptolemy. This book is about the motion of the sun, moon, Earth and planets in the universe. Ptolemy wrote this book in 140 A.D and in this book he put all the ancient knowledge related to geography and astronomy. One of the famous books of Ptolemy is named as "Tetrabiblos." In this book Ptolemy claimed that the transcribers of Babylon was instructed in 750 A.D in order to keep the detailed astronomical records. According to Ptolemy, the records were written on the clay tablets for about seven hundred years. Modern astronomers have confirmed the claimed by Ptolemy of recording information and observation of Venus and Mars during that time period. .
In Ptolemy line of thinking the earth is the center of the universe. Ptolemy first described all the description related to the earth-centered system as explained by the Aristotle and he also explores some of his observation as same as the Aristotle explores during his time period. Ptolemy proposed that earth is the centre of everythings who are revolving around it. In his view the planets in the universe are moving by their own and with different velocities. He also thinks that every planet in the universe is moving in the smaller sphere and he named this motion of planets around the world in sphere as epicycle. Ptolemy advocates many scientific laws and his magnitude scale of brightness is still using by many astronomers in order to calculate the distance of stars and distance between the stars.
According to Ashmand (1822), Ptolemy describes many proof, calculations and theorem and he also calculated the approximation of area of semicircle and the chord of the circle and these calculation are as given below:.
