Tithi

A tithi represents the time it takes for the Moon to gain 12 degrees of longitude over the Sun. There are 30 tithis in a complete lunar month, split across two pakshas — 15 in Shukla Paksha (waxing) and 15 in Krishna Paksha (waning). The sequence runs from Pratipada (1st) through Chaturdashi (14th) and culminates in Purnima (full moon) or Amavasya (new moon).

Each tithi carries its own character and is presided over by a specific deity. Certain tithis are considered highly auspicious for rituals — Ekadashi (11th) is sacred to Vishnu, Chaturthi (4th) to Ganesha, and Ashtami (8th) to Durga. Vratyas (fasting observances) and temple rituals across India are scheduled according to the tithi rather than the solar calendar date.

Tithimala computes the exact tithi using Swiss Ephemeris by calculating the true geocentric longitudes of the Sun and Moon at any given moment. The difference between the two longitudes, divided by 12, yields the current tithi number. Because the Moon's speed varies due to its elliptical orbit, tithis are not uniform in duration — some last over 26 hours while others are as short as 19 hours. This variability is why precise astronomical computation matters for determining the correct tithi at sunrise, which is the standard used in most North Indian panchang traditions.

Understanding which tithi is active at sunrise is foundational to the entire panchang system, since festivals, ekadashi fasts, and shraddha ceremonies all depend on it.