Poya is the name given to the Lunar monthly Buddhist holiday of Uposatha in Sri Lanka, where it is a civil and bank holiday. Full moon day is normally considered as the poya day in every month. 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.