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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 12 or 13 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.
Note that the "day" of the full Moon is not the same as the Gregorian Calendar day. In some cases the official date of a Poya public holiday in Sri Lanka is not on the Gregorian date of that full moon. For example, looking at the Department of Government Printing listing of "PUBLIC, BANK, MERCANTILE AND FULL MOON POYA HOLIDAYS – 2010", in January they list the full moon on January 30 but the Navam Full Moon Poya Day on January 29. The same discrepancy occurs in March, May, July, October and December of 2010. The actual holiday date is based on the phase of the moon at the Madhyahana time of day (the variant of Madhyahana which only covers 2 ghatikas). This is analogous to the rules that govern the date of Ganesh Chaturthi.[clarification needed]
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" (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. 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 12, see The Significance of Poya.
- For an example of the less common 13 full moon days in one year, see the 2009 calendar of "Sri Lanka Bank Holidays, Public Holidays & Full Moon Poya Days"