Pūrṇimā (Sanskrit: पूर्णिमा) is the word for full moon in Sanskrit. The day of Purnima is the day (Tithi) in each month when the full moon occurs, and marks the division in each month between the two lunar fortnights (paksha), and the Moon is aligned exactly in a straight line, called a syzygy, with the Sun and Earth. Full moon is considered the third of the four primary phases of the Moon; the other three phases are new moon, first quarter moon, and third quarter moon. The full moon shows 100% illumination, causes high tides, and can concur with lunar eclipses.[1]
Vat Purnima is celebrated on the full moon day of the month of Jyeshtha. Women pray for their husbands by tying threads around a banyan tree (Vat) on this day. It honours Savitri, the legendary wife of Satyavan who persuaded Yama to restore her husband's life.
Guru Purnima, devotees offer puja (worship) to their guru, on the full moon day of Ashadha. It is also known as Vyasa Purnima after the birthday of Vyasa, the author of the Mahabharata.
Sharad Purnima or Kojagiri Purnima, the autumn harvest festival, on the full moon day of Ashvina.
Shraddha Purnima is celebrated on the full moon day of the month of Bhadra. On this day, the Uma Mahesvara Vrata for the propitiation of the divine couple of Shiva Parvati is performed, as well as Shakra Vrata, where Indra is worshipped for children’s well-being.