Purnima

Pūrṇimā (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.

Festivals
The following festivals occur on the purnima. The Manava Purana (one of the Upapuranas) contains a list of the festivals that fall on the full moon.
 * Kartik Purnima, significant to both Vaishnava and Shaiva traditions, is celebrated on the full moon day of the month of Kartika. It is also called Tripura Purnima.
 * Shravana Purnima is the full moon day of the month of Shravana. This day has a number of different names. Hayagriva Jayanti and Gayatri Jayanti are also celebrated on Shravana Purnima. It also marks the occasion of Raksha Bandhan.
 * 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.
 * Buddha Purnima, marking the day of birth of Gautama Buddha, on the full moon day of Vaishakha. Kurma Jayanti is also celebrated on this day.
 * Holi/Phalguna Purnima, the spring festival of colours in Hinduism/Buddhism/Jainism, the full moon day of Phalguna.
 * Dattatreya Jayanti, commemorating the birth of the deity Dattatreya, is celebrated on the full moon day of the month of Margashira.
 * Hanuman Jayanti, making the birth of Hanuman, is celebrated on the full moon of the lunar month Chaitra. However, this is celebrated on different days in different states. While Orissa celebrates this as Vaisakha Sankranti, Andhra Pradesh celebrates Vaisakha Shukla Paksha Dashami, Kerala celebrates it in a previous month Margashira Amavasya coinciding with the Mula nakshatra. Chaitra Purnima is prescribed for the veneration of Chandra.
 * Shakambhari Purnima is celebrated on the full moon day of the month of Pausha, marking the descent of the goddess Shakambhari.
 * 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.