Artist's impression of Aryabhata, 5th century Hindu mathematician and astronomer. Aged 23, he wrote his major work \Aryabhatiya\" in 499 CE. It summarises Hindu mathematics up to that time and puts forward a number of innovations in mathematics and astronomy. He is credited with introducing the use of zero in a place-value system and was instrumental in the birth of trigonometry.He concluded that Pi is an irrational number and accurately worked out its value. His methods for making astronomical calculations were adopted throughout the Islamic World. He understood that the earth is a sphere and revolves on its axis; that the moon and planets are illuminated by the sun and that eclipses are caused by the shadow of the moon on the earth He accurately calculated the circumference of the earth. His work was fundamental in creating a new school of astronomy in South India."