Purnima (full moon)
Purnima is the full-moon tithi, the 15th and last of the bright half (Shukla paksha). It is a day of worship and fasting, and in the purnimanta calendar of North India it ends the lunar month.
Also known as: Poornima, Purnamasi, Pournami, Punam, Full moon tithi, Purnima vrat
Purnima covers the last 12° of the Moon’s journey away from the Sun, and the exact full moon comes at the moment the tithi ends. The panchang names the day by the tithi at sunrise. There are 12 or 13 Purnimas a year, each with its own observance, among them Guru Purnima, Raksha Bandhan, Sharad Purnima, Kartik Purnima, Holika Dahan and Buddha Purnima.
Many families keep a Purnima vrat and perform the Satyanarayan puja. Because the fast is often judged by the tithi at moonrise or in the evening, the Purnima vrat can fall a day before the date the calendar labels Purnima. Panchangs that list both are not contradicting themselves; ours marks the Purnima by its sunrise tithi and the Purnima Vrat by the tithi at moonrise.
In the purnimanta system used across most of North India, Purnima ends the month; in the amanta system it falls mid-month. Either way it is an auspicious day for worship, charity and holy bathing.