The six Ruthus
| Ruthu | Tamil months | 2026 Start |
|---|---|---|
| Ilavenil (spring) Vasantha Ruthu | Chithirai, Vaikasi | 14 April 2026, 12:09 AM |
| Muthuvenil (summer) Grishma Ruthu | Aani, Aadi | 15 June 2026, 3:30 AM |
| Kaar (rainy season) Varsha Ruthu | Avani, Purattasi | 16 August 2026, 10:36 PM |
| Koothir (autumn) Sarath Ruthu | Aippasi, Karthigai | 17 October 2026, 10:29 AM |
| Munpani (early winter) Hemantha Ruthu | Margazhi, Thai | 16 December 2026, 12:01 AM |
| Pinpani (late winter) Sisira Ruthu | Maasi, Panguni | 12 February 2026, 5:45 PM |
Equinoxes and solstices
| Event | Time | Day length |
|---|---|---|
| March equinox | 20 March 2026, 10:45 AM | 12:08 hours |
| June solstice | 21 June 2026, 4:25 AM | 14:54 hours |
| September equinox | 22 September 2026, 8:05 PM | 12:09 hours |
| December solstice | 21 December 2026, 3:50 PM | 9:26 hours |
Ayanam
- Uttarayanam
- 14 January 2026, 4:43 AM
- Dakshinayanam
- 16 July 2026, 2:16 PM
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.