c. 500

Aryabhatiya

Aryabhata (476–550)

The roots of astronomy in India were closely connected to the development of religion, as they were in most other early civilizations. Astronomical knowledge formed the foundation of early calendar systems that established dates for Hindu religious observances, or seasonal planting and harvesting. Just as in the West, advances over time in instrumentation used by clerics and early astronomers for charting the positions of the Sun, Moon, and stars led to the development of more sophisticated cosmological schemes for explaining and predicting the motions of the sky. The earliest of the great thinkers to make lasting contributions to the development of astronomy in India was the mathematician and astronomer Aryabhata, author of the oldest surviving Indian treatise on math and astronomy, the Aryabhatiya, published around the year 500.

Aryabhata essentially summarized all of mathematics in verse format in the Aryabhatiya, and included convenient new sine tables to use in trigonometric calculations. In the astronomy sections of the Aryabhatiya, Aryabhata explained eclipses as the logical result of shadows from the Earth or the Moon, rather than the work of sky demons. Using some of his newly developed spherical trigonometry calculations and eclipse measurements, he calculated the circumference of the Earth to an accuracy of less than 0.2 percent of its actual value, significantly improving upon the previous best estimate of the Earth’s circumference by Eratosthenes 750 years earlier.

Perhaps the most revolutionary aspect of Aryabhata’s thinking, though, was his claim that the Earth is not fixed in space but spins on its own axis, and that it is the stars in the celestial sphere that are fixed in space. Indian cosmology of Aryabhata’s time was definitively geocentric; while his own (accurate) calculations of planetary positions relied on orbits and epicycles similar to those in Ptolemy’s Almagest, Aryabhata was the first to advocate elliptical rather than circular paths for the planets. There are also suggestions in the Aryabhatiya, debated by scholars interpreting the original language and meaning, that Aryabhata believed in a sun-centered cosmos. Like those of Aristarchus in Greece, however, such radical heliocentric ideas would take more than a thousand years to catch on in India.

Statue of the mathematician and astronomer Aryabhata at the Inter-University Centre for Astronomy and Astrophysics in Pune, India.