Tithis

A tithi is a lunar day in the Hindu calendar: the time it takes the angular distance between the Sun and Moon to increase by twelve degrees. Because the Moon's motion is uneven, tithis vary in length and do not align neatly with solar days, a tithi may be a little shorter or longer than a day, and one can occasionally be skipped or repeated.

There are thirty tithis in a lunar month, fifteen in the waxing fortnight (shukla paksha) and fifteen in the waning (krishna paksha), each with a name and a character, and many Hindu festivals and observances are fixed to a particular tithi rather than to a solar date.

Because so much of Hindu religious life is scheduled by tithi (Ekadashi fasts on the eleventh, Purnima on the full moon, Amavasya on the new), the tithi is the practical unit of the ritual calendar, and each carries associations of favourability for particular acts. The tithi is also one of the five limbs of the panchanga, the Hindu almanac.

The atlas gives each tithi its name, its fortnight, and its associations and observances. The tithi is divided into karanas and works alongside the nitya yogas, each treated in its own category, within the calendar and Vedic material.