Tamil calendar
The days of week (Kizhamai) in the Tamil Calendar relate to the celestial bodies in the solar system: Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn, in that order. The week starts with Sunday. The number of days in a month varies between 29 and 32. These are the months of the Tamil Calendar. Note: The Sanskrit month starts a few weeks ahead of the Tamil month since the Tamil calendar is a solar calendar while the Sanskrit calendar is a lunisolar calendar The Tamil year, in keeping with the old Indic calendar, is divided into six seasons, each of which lasts two months: The 60-year cycle is common to both North and South Indian traditional calendars, with the same name and sequence of years. Its earliest reference is to be found in Surya Siddhanta, which Varahamihirar (550 CE) believed to be the most accurate of the then current theories of astronomy. However, in the Surya Siddhantic list, the first year was "Vijaya" and not "Prabhava" as currently used. There are some parallels in this sexagenary cycle with the Chinese calendar. The Surya Siddhanta and other Indian classical texts on astronomy had some influence on the Chinese calendar although it merits attention that the sexagenary cycle in China is itself very old. After the completion of sixty years, the calendar starts a new with the first year. This corresponds to the Hindu "century." The "Vakya" or "Tirukannitha Panchangam" (the traditional Tamil almanac) outlines this sequence. It is related to the position of the planets in the sky with respect to earth. It means that the two major planets Sani/Saturn (which takes 30 years to complete one cycle round the sun) and the Viyazhan/Jupiter (which takes 12 years to complete one cycle round the Sun) comes to the same position after 60 years. The following list presents the current 60-year cycle of the Tamil calendar: The months of the Tamil Calendar have great significance and are deeply rooted in the faith of the Tamil Hindus. Some months are considered very auspicious while a few are considered inauspicious as well. Tamil months start and end based on the Sun's shift from one Rasi to the other but the names of the months are based on the star on the start of Pournami in that month. The name of the month is some times the name of the star itself. (e.g. Chithrai is always the star on the Pournami of the Chithirai month). Some of the celebrations for each month are listed below. Dates in parentheses are not exact and usually vary by a day or two. Underneath (or beside) the months of the Hindu calendar are their Gregorian counterparts. The Tamil Calendar is important in the life of Tamil-speaking people and most Festivals of Tamil Nadu are based on it. Some Festivals include 



One day was even dedicated to a celebration of the Tamil alphabet and was called "ezhuthu naal'.
Sixty-year cycle
There are several references in early Tamil literature to the new year.