When is New Year's day? Well, that depends on who you ask. For many in the north, Diwali is New Year's day. But it falls on different days each year. The Tamil, Malayalees, Punjabis and Assamese celebrate their New Year on 14 April. But the Telugus, Kannadigas and Maharashtrians celebrate their New Year on different dates. How are these dates determined and why are calendars so different for people in the same country? This story will you through time of how calendars evolved, how ancient Indians and people across the world measured time.