A Poya occurs every full moon. Uposatha is important to Buddhists all around the world, who have adopted the lunar calendar for their religious observances. Owing to the moon's fullness of size as well as its effulgence, the full moon day is treated as the most auspicious of the four lunar phases occurring once every lunar month (29.5 days) and thus marked by a holiday.
Every full moon day is known as a Poya in the Sinhala language; this is when a practicing Sinhalese Buddhist visits a temple for religious observances. There are 13 or 14 Poyas per year. The term poya is derived from the Pali and Sanskrit work uposatha (from upa + vas "to fast"), primarily signifying "fast day". Generally shops and businesses are closed on Poya days, and the sale of alcohol and meat is forbidden.
The Poya Day in each month generally falls on the Gregorian date of the full moon but occasionally it falls a day either side. The designated Poya Day is based on the phase of the moon at the Madhyahana time of day (the variant of Madhyahana which only covers two ghatikas). This is analogous to the rules that govern the date of Ganesh Chaturthi.[clarification needed]
|Month||Poya Name||Full Moon Poya days of 2019|
If a month has two Poya days, the name of the second one will be preceded by "Adhi" ("extra" in Sinhala) as in "Adhi Vesak", "Adhi Poson", etc.
- "Sri Lanka Bank Holidays, Public Holidays & Full Moon Poya Days" Archived 2011-03-01 at the Wayback Machine (Online Calendar for years 2003–2011), Ministry of Public Administration and home Affairs, Independence Square, Colombo 7, Sri Lanka.
- "Sri Lank Desk Calendar - 2013, Buddhist Era 2556-2557" (PDF). Department of Government Printing. Archived from the original (PDF) on 30 July 2013. Retrieved 16 September 2013.
- A.G.S. Kariyawasam, "Buddhist Ceremonies and Rituals of Sri Lanka" (Ch. 3), The Wheel Publication No. 402/404 (Kandy: Buddhist Publication Society, 1995). Access to Insight, 1 March 2011
- For a standard listing of the 13, see The Significance of Poya.
- For an example of the less common 14 full moon days in one year, see the 2009 calendar Archived 2011-01-24 at the Wayback Machine of "Sri Lanka Bank Holidays, Public Holidays & Full Moon Poya Days"
- Government Notifications, Democratic Socialist Republic of Sri Lanka ", The Gazette of the Democratic Socialist Republic of Sri Lanka, EXTRAORDINARY", 10 May 2018.