Aryabhata, When was he born?

Aryabhata, the author of Aryabhatiya is sometimes confused with his namesake of the tenth century AD, the author of Maha-siddhanta (महा सिद्धांत). The author of Aryabhatiya is called Aryabhata I. In stanza 1 of chapter ii of the Aryabhatiya, he writes :

Aryabhata  sets forth here the knowledge honoured at Kusumapura. 

 Many other commentators Paramesvara (AD 1431), Raghunatha-raja (AD 1597), and persian scholar Al-Biruni (AD 973-1048) confirm the fact that he was Aryabhata of Kusumapura. Bhaskara I (AD 629), the earliest commentator of Aryabhatiya, refers to Aryabhata I as Asamaka, his Aryabhatiya by the names Asmaka-tantra and Asmakiya, and identifies Kusumapura with Pataliputra in ancient Magadha. 

When the methods of the five Siddhanta began to yield results conflicting with the observed phenomena such as the settings of the planets and the eclipses, etc, there appeared in the Kali age at Kusumapuri, Surya himself in the guise of Aryabhata, the Kulapa well versed in astronomy.

 There is a verse in Aryabhatiya which  runs as follows:

When sixty times sixty years and three quarter-yugas had elapsed (of the current yuga), twenty-three years had then passed since by birth. This shows that Kali year 3600 elapsed and at that time Aryabhata was twenty seven years old. Kali year 3600 corresponds to AD 499, that implies that Aryabhata was born in year AD 476, incidentally that is the same year Buddhagupta took over the reigns of government at Pataliputra.

The Bihar Research Society, Patna, celebrates the birth anniversary of Aryabhata on April 13.