Changes: Thiruvalluvar Calendar

Revision as of 06:12, 23 April 2020

Thiruvalluvar Calendar was created by Arivumani Velmurugan to bring the Tamil culture into the world. Currently Sidereal based calendars are used as Tamil Calendar. This calendar not aligns with Current Gregorian Calendar which is used in worldwide. It does not have fixed leap year system and fixed number of days per month.

This calendar is based on Thiruvalluvar Era (31 BCE). Currently Tamilnadu (India) Government has following Thiruvalluvar based Tamil Sidereal calendar system. In this calendar, 13 months are introduced instead of conventional 12 month system. 365 days are equally distributed in 12 months except first month. So first month is designed as leap month which has 29 days in normal year and 30 days in leap year.

In 400 year cycles, 4800 (12x400) months out of 5200 (13x400) are equal unique months of 28 days (92.3%). 303 months out of 5200 has 29 day months (5.8274%). 97 months out of 5200 has 30 day months (1.87%).

New Year Day

The calendar always starts on January 15 every year (Approximate date for Thiruvalluvar Day). Gregorian New year also falls on 13th month of 15th day in Tamil Calendar. Tamil cultural festivals are most concentrated in the month of 'Thai'. So the calendar is made to start on Thai 1 / January 15.

Calendar Structure
No	Month name	Gregorian start date	Days per month
1	Paamathi (பாமதி)	Jan 15	29/30*
2	Ilmathi (இல்மதி)	Feb 13/14*	28
3	Thuramathi (துறமதி)	Mar 13	28
4	Uzhmathi (ஊழ்மதி)	Apr 10	28
5	Arasumathi (அரசுமதி)	May 8	28
6	Amaichumathi (அமைச்சுமதி)	Jun 5	28
7	Aranmathi (அரண்மதி)	Jul 3	28
8	Koozhmathi (கூழ்மதி)	Jul 31	28
9	Padaimathi (படைமதி)	Aug 28	28
10	Natpumathi (நட்புமதி)	Sep 25	28
11	Kudimathi (குடிமதி)	Oct 23	28
12	Kalamathi (களமதி)	Nov 20	28
13	Karpumathi (கற்புமதி)	Dec 18	28
	Total		365/366*

- In leap years.

Month

There are various type of months used in calendars. Mainly Synodic months are used in most of calendars (29/30 days=Average of 29.53058). In solar calendars, 30 day months and 31 day months are used. No calendar shows sidereal month, tropical month, anomalistic month and draconic month. These months are having 27+x days. So 28 day month approximates these type of months. So it is approximately relates to sidereal.

Day and Week

Most of the calendars in the world uses the week of 7 day cycle. This week cycle is uninterrupted. Year of 365 and 366 days are not fit entirely into the week cycle. Two additional weekdays (Days out of week cycle) are assigned to additional days.

Weekday names are derived from Thirukkural Chapters starting with vowels.

Weekday	W1	W2	W3	W4
Aranthinam (அறந்தினம்)	1	8	15	22
Aalvinam (ஆள்வினம்)	2	9	16	23
Idanthinam (இடந்தினம்	3	10	17	24
Eegaithinam (ஈகைதினம்)	4	11	18	25
Uzhavinam (உழவினம்)	5	12	19	26
Ukinam (ஊக்கினம்)	6	13	20	27
Otrinam (ஒற்றினம்)	7	14	21	28
Kurunthinam (குறுந்தினம்)	Once in a Year			Paamathi 29
Nedunthinam (நெடுந்தினம்)	Once in a Leap Year			Paamathi 30

In this calendar, All dates are permanently fixed with weekdays. Every Year, Every Month and Every week starts with Aranthinam and ends with otrinam (Except First Month).

Features

The calendar has two type of months. One type is Normal Months (2-13) have 28 days each (Exactly 4 weeks). Another type of month is Leap month i.e., First month. First month is larger than other months dedicated to God.
Month names are derived directly from 13 episodes of Thirukkural.
Starting Weekday in the all months are same. The same structure because of 4 weeks (28 Days).
Day to Day calculation, Weekday finding methods are so easy compared to Current Civil Calendar.
13 months is very special for us. In Tamil letters includes 12 vowels and 1 ayutha letter. Tamil calendar (Thasathi) includes 12 months of 28 days and one month of 29 or 30 days.
Total Tamil letters are 247=13x19. 2+4+7=13. So 13 is the best Tamil number. This number is unlucky for some countries.
28 division clock is enough to show 28 days, 14 month divisions (13 months of 28 days +Additional Leap days), and 7 weekdays. 28:14:7 = 4:2:1
Year is divided into 4 quarters.
1. First Quarter: Paa(1) 1 - Uzh(4) 6 = 91/92 Days (Paavoozh)
2. Second Quarter Uzh(4) 7 - Aran(7) 13 = 91 Days (Uzharan)
3. Third Quarter Aran(7) 14 - Natpu(10) 20 = 91 Days (Natparan)
4. Fourth Quarter Natpu(10) 21 - Karpu(13) 28 = 92 Days (Natkarpu)