The Tamil Panchangam is an astronomical calendar rooted in the sidereal zodiac (Nirayana system). Unlike the Gregorian solar calendar which adds a leap day every four years to stay aligned with the tropical year, sidereal astronomical calculations track the Sun's position relative to fixed background stars along the ecliptic.
The Solar-Lunar Dual Axis
The calendar operates on a dual axis:
- Solar Calendar (Sauramana): Determines the 12 Tamil months (Chithirai, Vaikasi, Aani, Aadi, Avani, Purattasi, Aippasi, Karthigai, Margazhi, Thai, Masi, Panguni). Each solar month begins precisely when the Sun transitions (Sankramanam) into a new zodiac sign.
- Lunar Calendar (Chandramana): Determines daily Tithis (lunar phases), festivals, and religious rituals calculated from the angular separation between Sun and Moon.
Thirukanitha vs. Vakya Panchangam
In South India, two computational schools exist. Vakya Panchangam utilizes ancient poetic mnemonic verses. Thirukanitha Panchangam updates planetary position tables continuously using modern trigonometric astronomy data.