The six Ruthus
| Ruthu | Tamil months | 2027 Start |
|---|---|---|
| Ilavenil (spring) Vasantha Ruthu | Chithirai, Vaikasi | 14 April 2027, 1:05 PM |
| Muthuvenil (summer) Grishma Ruthu | Aani, Aadi | 15 June 2027, 4:32 PM |
| Kaar (rainy season) Varsha Ruthu | Avani, Purattasi | 17 August 2027, 11:50 AM |
| Koothir (autumn) Sarath Ruthu | Aippasi, Karthigai | 17 October 2027, 11:45 PM |
| Munpani (early winter) Hemantha Ruthu | Margazhi, Thai | 16 December 2027, 2:15 PM |
| Pinpani (late winter) Sisira Ruthu | Maasi, Panguni | 13 February 2027, 7:45 AM |
Equinoxes and solstices
| Event | Time | Day length |
|---|---|---|
| March equinox | 20 March 2027, 11:24 PM | 12:07 hours |
| June solstice | 21 June 2027, 5:10 PM | 13:43 hours |
| September equinox | 23 September 2027, 9:01 AM | 12:07 hours |
| December solstice | 22 December 2027, 5:42 AM | 10:34 hours |
Ayanam
- Uttarayanam
- 14 January 2027, 6:47 PM
- Dakshinayanam
- 17 July 2027, 3:25 AM
How it is calculated
Each Ruthu is two Tamil months. A new Ruthu begins when the Sun enters Mesham, Mithunam, Simmam, Thulam, Dhanusu or Kumbam.
At an equinox, day and night are nearly equal. At the June solstice the day is longest in India; in December it is shortest. These are astronomical (Sayana) figures.
In the panchangam, Uttarayanam begins on Thai 1 and Dakshinayanam begins on Aadi 1.