Nisathi Calendar!

 Current Tamil Calendar is based on Hindu Sidereal Solar calendar of 12 months. each month has the length varies from 29 days to 32 days. Length of mean sidereal year varies with every year. It is the accurate calendar but not able to predict by normal human. So New international calendar is created initially in Tamil from the honor of Thiruvalluvar who creates the Thirukkural (World Common Divine Book). This calendar is the Tropical Solar Calendar which is permanently synchronised to Gregorian Calendar (International Civil Calendar). The calendar uses 13 chapter groups of Thirukkural as Months. So every month has 28 days except first month. First month has 29 days in Normal Year and 30 days in Leap Year. Every day is fixed with weekday which is not possible in other calendars. Year:        Year of this calendar is based on Thiruvalluvar Era (31 BCE). Thiruvalluvar year is calculated by adding the common era into 31. The leap year rule is same as Gregorian calendar. A Tropical year has 365.2425 days long which completes in 400 year cycles.

 Month:        If we divide the year into 13 months, the solar month has the average length of 28.095577 days (28.077 in Normal year and 28.1538 in Leap year). The average is nearest to the integer 28. Also 28 days will be evenly distributed as 4 weeks as February Month. So we make the calendar with 13 months distributed with 28 days each. Error = 365.2425 – 364 [13×28] = 1.2425 Days. The error days are added in the end of first month to align with existing Gregorian calendar. First month has 29 days in Normal and 30 Days In Leap Year.Maximum Days = 28 (All months from 2 to 13), 29 (If M==1, Year is Normal), 30 (If M==1, Year is Leap)
        The months with 28 days will approximate the length of sidereal month (27.32166 Days), Tropical Month (27.32158 Days), Anamolistic Month (27.21222 Days) and Draconic Month (27.55455 Days). Second month is the approximation of synodic month 29/30 days(29.53059 Days).         The month Names will be derived from Thrukkural Cahpter Groups. Every name ends with ‘Mathi’. Mathi is defined as the cycle of Lunar Mansions. Mathi is tamil name of Moon. 

Weekday:        Currently we are using 7 day weeks in all type of calendars. Only names are changed. This 7 week dates are not exactly fit in 365 days and 366 days calendar. Weekdays are formed using the names of Sun, Moon and other planets.         In this calendar, weekdays are selected from 133 chapter groups starts with vowels. Names of weekdays ends with ‘Thinam’ which stands for ‘Day’. All months except first month has 28 days fits into 7 weekdays. Additional days added in the end of first month are assigned to special weekdays out of common weekdays.