(1)THE HINDU ASTRONOMICAL SIGNIFICANCE OF THE TAMIL NEW YEAR
The Earth travels in an eliptical path around the Sun through 360 degrees (Paakai in Tamil), and the time period for one such complete travel around the Sun (Suriyan in Tamil) is called an Year (Aandu in Tamil).
The circumferance of the eliptical path traced by the Earth (Ulaham in Tamil) having the Sun as the central point - are divided into twelve arcs, and the angular segments traced by each arc measuring 30 degress is called a House (Veedu in Tamil or Rasi in Sanskrit). Thus the earth passes through twelve Houses in an year.
In actual fact, it is the Earth which enters each Houses at any given time. But for us who live on the Earth it appears as if the Sun is moving (relative Motion), and we very loosely say that the Sun travels through the twelve Houses.
The twelve Houses are named as,
(1) Meda Veedu or Rasi (2) Idapa Veedu or Rasi (3) Mithuna Veedu or Rasi (4) Kataka Veedu or Rasi (5) Singa Veedu or Rasi (6) Kanni Veedu or Rasi (7) Thula Veedu or Rasi (8) Virutchika Veedu or Rasi (9) Thanu Veedu or Rasi (10) Kumba Veedu or Rasi (11) Makara Veedu or Rasi (12) Meena Veedu or Rasi
The Earth moving in to Meda Veedu or Rasi, is taken as the starting point of it's next complete cycle in an eliptical path around the Sun.
The period of travel of the Earth in each Veedu or Rasi is known as a Thingal - a Month (also known as Matham in Tamil and Masa in Sanskrit). Hence for the earth to travel through the twelve Veedus or Rasis, it takes twelve Thingals to complete one cycle, which is known as an Aandu - a Year (also known as Varudam in Tamil and Varusha in Sanskrit).
The time the Sun enters the Meda Veedu or Rasi is taken as the starting point of the New Year (Puthiya Aandu Pirappu or Varusha Pirappu), and this starting month is called as the Chithirai Thingal or Matham.
The one who calculates the astronomical settings and movements of the Earth, Sun, and other Planets in respect of the 12 Veedus or Rasis are known as the Jothidar (Saaththriyaar - in Jaffna). But in ancient times in Tamil Nadu they were known as the Kaalak Kanithar.
(2) THE TAMIL SEASONAL SIGNIFICANCE OF THE TAMIL NEW YEAR
The Tamils have divided an Aandu in to six seasons based on the climatic conditions in Tamil Nadu. They are namely the,
Ilavenil Kaalam : mild sunny period : Chithirai, Vahasi - Thingal : mid April to mid June Muthuvenil Kaalam : intense sunny period : Aani, Aadi - Thingal : mid June to mid August Kaar Kaalam : cloudy rainy Period : Aavani, Purataasi - Thingal : mid August to mid October Kuthir Kaalam - cold period : Iyppassi, Kaarthihai - Thingal : mid October to mid December Munpani Kaalam - early misty period (evening dew): Maarkali, Thai - Thingal : mid December to mid February Pinpani Kaalam - late misty period (morning dew): Maasi, Panguni - Thingal : mid February to mid April
The beginning of the Ilavenil Kaalam of the Tamils coincides with the beginning of the Sun moving into the Meda Veedu or Rasi, which falls in mid April, and is the time of commencement of the Tamil month of Chitirai.
The dawn of the month of Chithirai is the dawn of the Ilavenil Kaalam, a period of mild sun with much light and less humid wind known to be very soothing and refreshing and was known as Thentral Kaatru to Tamils.
This might be the very reason the Tamil Saiva Saint of Tamil Nadu namely the Thirunaavukkarsu Nayanaar of the mid seventh century, equated the pleasure of being at the feet of the God Siva which is as good as the extended Ilavenil Kaalam, showing the great delight the Tamils had during the Ilavenil Kaalam.
So the Tamils selected the dawn of this Ilavenil Kaalam as the dawn of the Tamil New Year.
(3)THE TAMIL (OR HINDU ???) CYCLIC SYSTEM OF YEARS
The Tamils also considered an average life cycle of a human-being as 60 years, and reckoned a "Cyclic System of Years" based on same provided with different names for each year falling within this cycle. The Year Cycle repeats itself in every 60 years. The names of the sixty years of this cycle are as follows.
According to the above Cyclic System of Years, the Tamil New Year the "Thaarana Aandu" dawns on the first day of the Chiththirai Thingal, which is the 13th of April 2004.
Constructive Comments on same are welcome, as some claim it is a Hindu New Year and the Tamil New year actually falls on the 14th of January with the dawn of the Tamil month of Thai.
Very informative along with your add-on to Pavithra. Saha clarification was interesting.
In Tamil inscriptions, observes Kudanthai Sethuraman, there are two ways of mentions : one is Aandu : "Swasthi shree ko rajakesarivarmarkku aandu ... (5th).. " This means the calculation of year is from the Saha (Tamil ) year of the King's ascendancy...
Another is Yaandu : ""Swasthi shree ko rajakesarivarmarkku Yaandu ... (5th).. " The calculation from the date (year) of ascendancy ...
Eg: If RR asdended on the 26th June 985, (saha xxx ), 2nd aandu will be saha + 2; Yaandu will be 26.6.985 + 2. Based on this, he is made several astronomical (!) calculations and put foward various dates ... in his Books "the Cholas" etc.