The moon completes one full cycle from new to full approximately every 29 days.
Every full moon is the completion of a single lunation - one synodic month.
Sahasra Purna Chandrodayam (or Sahasra Chandra Darshan) is the celebration of a person's 1000th full moon during his or her life as a special occasion. This is a custom in parts of the state of Maharashtra in India and Nepal. The time between similar lunar phases, the synodic month, is on average 29.53 days, and thus 1000 moons equals 29530 days = 80.849 years = approximately 80 years, 10 months on the Western calendar. In practice the celebration traditionally is held 3 full moons before a person's 81st Birthday. This ritual is also known as Sahasra Chandra Darshan (सहस्र-(पूर्ण)चन्द्र-दर्शन) or Chandra Ratharohan Nilu Damle writes that the ritual is to provide strength to the person up to the end of their life, lessen their ego, provide strength to them while a foetus in their mother's womb, and be strong at birth.
In Sanskrit sahasra means 1000, purna means full, and chandrodyam means dawn of moon.
From Wikipedia https://en.wikipedia.org/wiki/Sahasra_purna_chandrodayam
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