Vedic · Glossary
Tithi · the lunar day
A lunar day, measured by the angle between the Sun and the Moon.
Reading
A tithi is a lunar day, the unit the Moon’s phase makes rather than the one the turning Earth makes. It is measured as the angle between the Sun and the Moon, counted in steps of twelve degrees, so that thirty tithis fill the space from one new moon out to full and back to dark.
Fifteen tithis carry the Moon from new to full as it waxes, the śukla pakṣa, and fifteen carry it back to dark as it wanes, the kṛṣṇa pakṣa. Because the Moon does not travel at an even speed, a tithi is not a fixed number of hours; it stretches and shrinks against the clock.
It measures time by the light on the Moon, not by the turning of the Earth.
The tithi is the first of the five limbs of the pañchāṅga and the one most watched in timing. Classically each tithi carries its own temper, some read as full and favorable, some as lean, and the choosing of times weighs the day’s tithi first.
Where it rhymes
The same archetype, spoken in other systems.