Āryabhata (born, 476 CE) is perhaps the foremost among the Indian mathematician-astronomers. His work Āryabhaṭīya composed at the age of 23, commences with this interesting invocation.

प्रणिपत्यैकमनेकं कं सत्यां देवतां परं ब्रह्म ।
आर्यभटस्त्रीणि गदति गणितं कालक्रियां गोलम् ।।

Here, besides conveying his reverences to the devata, Āryabhata also gives an outline of the text itself. Some of the main contributions of Āryabhata include providing a very good approximation to the value of pi, a harmonic equation in its finite difference form to determine first-order sine-differences, methods for resolving problems pertaining to mensuration, root extraction and so on. From the viewpoint of physics, his ideas on the nature and division of time, source of light on the moon, spinning of the Earth on its axis, are all quite intriguing and remarkable. The value of the sidereal year given by him was extremely accurate and so too the revolution periods of the various planets.

The book Āryabhatīya is divided into four parts. The first part, Gītikā, provides a variety of important astronomical parameters. The second part, Gaṇita, deals with mathematics. The third part, Kālakriyā, deals with the determination of the true position of the Sun, the Moon, and the planets by means of epicycles. The fourth part, Gola, deals with description of planetary motions on the celestial sphere, which includes a succinct description of the phenomenon of the eclipse as well. During the talk we will be highlighting some of these aspects.

Guest Speaker: Prof. K. Ramasubramanian, IIT Bombay

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