Tamil calendar

The Tamil calendar is a sidereal Hindu calendar used in Tamil Nadu, India. It is also used in Puducherry, and by the Tamil population in Malaysia, Singapore, Mauritius and Sri Lanka. Tamil Nadu farmers greatly refer to this. It is used today for cultural, religious and agricultural events, with the Gregorian calendar largely used for official purposes both within and outside India. The Tamil calendar is based on the classical Hindu lunisolar calendar also used in Assam, West Bengal, Kerala, Manipur, Nepal, Odisha, Rajasthan and Punjab.

There are several festivals based on the Tamil Hindu calendar. The Tamil New Year follows the nirayanam vernal equinox and generally falls on 14 April of the Gregorian year. 14 April marks the first day of the traditional Tamil calendar and this remains a public holiday in both Tamil Nadu and Sri Lanka. Tropical vernal equinox fall around 22 March, and adding 23 degrees of trepidation or oscillation to it, we get the Hindu sidereal or Nirayana Mesha Sankranti (Sun's transition into nirayana Aries). Hence, the Tamil calendar begins on the same date in April which is observed by most traditional calendars of the rest of India - Assam, Bengal, Kerala, Odisha, Manipur, Punjab etc. This also coincides with the traditional new year in Burma, Cambodia, Laos, Sri Lanka, Bangladesh Nepal and Thailand. The 60-year cycle is also very ancient and is observed by most traditional calendars of India and China, and is related to 5 revolutions of Jupiter according to popular belief, or to 60-year orbit of Nakshatras (stars) as mentioned in Surya Siddhanta.

...
Wikipedia