तिथि Tithi

A tithi is a lunar day — one step in the Moon's monthly dance away from and back to the Sun. Thirty tithis make a lunar month, and they set the rhythm of festivals, vrats, and auspicious timing. Unlike the fixed 24-hour day, a tithi is defined by the sky: it is the time the Moon takes to pull a further 12° ahead of the Sun, so its length stretches and shrinks as their speeds change. Fifteen tithis carry the Moon from new to full through the bright fortnight (shukla paksha), waxing toward Purnima; fifteen more wane through the dark fortnight (krishna paksha) back to the new-Moon Amavasya. Each has its own character and presiding deity, and it is this lunar rhythm — not the solar date — that sets most festivals, fasts (vrats) and traditional observances. When someone asks the 'lunar date' of a birth or a festival, the tithi is the answer, and choosing an auspicious moment almost always begins by choosing a favourable one.