In Vedic astrology, a lunar month is named after the Nakshatra in which the Moon is full (Purnima). Purnimanta months (celebrated in North India) end on the Full Moon (Purnima), with Krishna Paksha as the first fortnight. Amanta months (celebrated in South and Western India) end on the New Moon (Amavasya), starting with Shukla Paksha.

A Tithi is a lunar day representing a 12° angular displacement of the Moon ahead of the Sun (Moon Longitude - Sun Longitude) ÷ 12°. Because the Moon moves at variable orbital speed (~11.8° to 15.2° per day), Tithis can range from 19 to 26 solar hours, creating Kshaya (skipped) and Vriddhi (extended) Tithis.

The moment the Sun crosses from one sidereal Rashi (zodiac sign) into the next is called Sankranti. There are 12 Sankrantis in a year. The 16 Ghati period (~6.4 hours) around the transit is considered Punya Kaal for spiritual austerities, charity, and holy dips.

The Moon traverses approximately 13°20' (one Nakshatra) every day and stays in one Rashi (30°) for about 2.25 days. When the Moon crosses into a new Rashi, the exact time is highlighted in the calendar cell (e.g. 🌙 Kanya 25:26+).