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. Tamilnadu 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 solar 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. The traditional Tamil year starts on 14 April 2015, Kaliyuga 5117. Vikrama and Shalivahana Saka eras are also used. There are several references in early Tamil literature to the April new year. Nakkirar, the author of the Nedunalvaadai writes in the 3rd century that the Sun travels from Mesha/Chitterai through 11 successive Raasis or signs of the zodiac. Kūdalūr Kizhaar in the 3rd century refers to Mesha Raasi/Chitterai as the commencement of the year in the Puranaanooru. The Tolkaapiyam is the oldest surviving Tamil grammar that divides the year into six seasons where Chitterai marks the start of the Ilavenil season or summer. The 8th century Silappadikaaram mentions the 12 Raasis or zodiac signs starting with Mesha/Chitterai. The Manimekalai alludes to the Hindu solar calendar as we know it today. Adiyaarkunalaar, an early medieval commentator or Urai-asiriyar, mentions the 12 months of the Tamil Hindu calendar with particular reference to Chitterai. There were subsequent inscriptional references in Pagan, Burma dated to the 11th century CE and in Sukhothai, Thailand dated to the 14th century CE to South Indian, often Vaishnavite, courtiers who were tasked with defining the traditional calendar that began in mid-April.
