# Ancient Astronomy Observations: Ptolemy and Aryabhata

According to Ptolemy, the Earth was at the center of the universe and the Sun and other planets revolved around the Earth. In this article, you will encounter the astronomy views of Ptolemy and Aryabhata.

2nd century AD , Ptolemy

Possessing Greek or Egyptian ancestry, Ptolemy was a Roman citizen who became well versed in the ways of math, astronomy, geography, and astrology.

Ptolemy would go on to write the ‘Planetary Hypotheses,’ which elaborated on his previous theories related to the mathematical model he used to prove his thoughts regarding the universe. He went on to compute the dimensions of the universe and eventually estimated that the Sun was at “an average distance of 1210 Earth radii while the radius of the sphere of the fixed stars was 20,000 times the radius of the Earth.”

However, one of his most useful achievements concerning astronomy was his “Handy Tables” , a tool he created for astronomical calculations that presented data in such a way that he could easily compute the positions of the Sun, Moon and planets. The tables also addressed the rising and setting of the stars, as well as shed light on when eclipses of the Sun and Moon would take place. This table would later serve as a model for other astronomical tables in the future. Another useful tool of Ptolemy’s was his star calendar (or almanac), which was based on the behavior of stars over the course of the solar year.

~ 5th century , Aryabhata

While Aryabhata is best known for theorizing that the Earth was at the center of the universe, he is often seen as upholding a form of the heliocentric model without even knowing it. Aryabhata was the first of notable mathematicians and astronomers belonging to the classical age of Indian thought and research.

Aryabhata seemed to believe that the earth rotated about its axis where he described the movement of the stars as a relative motion caused by the rotation of the earth, comparing it to “like a man in a boat moving forward sees the stationary objects as moving backward.” Contradicting his previous assertion, statements to follow would point to a more heliocentric train of thought.

When describing the solar system, Aryabhata stated that the Sun and Moon each moved with the help of epicycles , a model used to refer to the variation of speed and direction of the Sun, Moon and planets. This model meant that other celestial objects revolved around the Earth.