Vedic astrology · glossary
Tithi
A lunar day: one of 30 phases defined by each 12° of the Moon's separation from the Sun.
What it means
A tithi advances each time the Moon gains 12° on the Sun, so 30 tithis span a full lunar month — 15 in the waxing fortnight (śukla pakṣa) and 15 in the waning (kṛṣṇa pakṣa). Because the Moon's speed varies, a tithi is not a fixed number of hours; a panchāṅga reports the clock time each tithi ends ("upto HH:MM").
How it's computed
The engine takes the sidereal longitudes of the Moon and Sun, computes their difference modulo 360°, and divides by 12° to get the tithi index; the end-time is found by bisecting to the next 12° crossing.
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Frequently asked
- Why does a tithi not match a calendar day?
- The Moon moves at a varying rate, so a tithi can run from a few hours to over a day, and can begin or end at any clock time.
- What are pakṣa and Amāvāsya?
- Pakṣa is the fortnight — śukla (waxing) or kṛṣṇa (waning). Amāvāsya is the new-moon tithi and Pūrṇimā is the full moon.