A calendar divides the year into seasons, months and days helping us to know the time or 'Kaalam theri'.

Nimrod or Murugan, the first king of Babylon, was a great astronomer too. He is said to have drawn the Solar Calendar (Kalam theri – Kalandheri – calendar) that would help in planned cultivation of crops by the farming community that was emerging post the Flood. It was based on the solstices and the equinoxes with respect to the earth and the sun. He named the twelve months of the year in Thamizh based on the respective star / constellation that fall on the same plane of the sun so that the sun seemed to move from house to house twelve times in a year in a complete cycle. He was an Aasevaha Sitthar (like Easwaran/ Sivan of old) who had mastered various arts and higher sciences and who were supposed to provide solution to every problem of man on earth. Even today, the solar year that he put together is called the Sidereal (Siddhareal) year. (Interestingly, Sivan and Tammuz are names of months in the Jewish calendar even today!)

Thamizh year begins on the 14th of April now but it was originally on the 21st of March, the summer equinox day. (It has shifted little by little over four thousand years to the current date). Romans shifted the beginning of the year to January approximately two thousand years after the first calendar was drawn.