What is a Tithi?

A tithi is a lunar day, defined by the angle between the Moon and the Sun. Each time the Moon moves 12 degrees further from the Sun, one tithi completes. Because the Moon's speed varies, a tithi can be slightly shorter or longer than a solar day.

Every lunar month has two fortnights: Sud (the bright half, from new moon to full moon) and Vad (the dark half, from full moon back to new moon).

All our festivals follow tithis: Janmashtami falls on Shravan Vad 8, and Diwali on the Amas (new moon) of Aso.