The ancient Tamil calendar was based on the sidereal year similar to the ancient Hindu solar calendar, except that months were from solar calculations, and originally there was no 60 year cycle as seen in Sanskrit calendar. The year was made up of twelve months and every two months constituted a season.
With the popularity of Mazhai vizhavu, traditionally commencement of Tamil year was clubbed on April 14, deviating from the astronomical date of "vadavazhi vizhavu".


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