The fifteenth of August is the heaviest single date in the month's religious calendar. The Catholic Church keeps it as the Assumption of Mary, the taking of the Virgin body and soul into heaven, defined as dogma by Pius XII in 1950 though celebrated on the date for well over a millennium before. The Orthodox East keeps the same day as the Dormition of the Theotokos, her falling asleep, and prepares for it with a strict two week fast from the first of the month, so that the whole first half of August in Orthodox practice leans toward the feast. Nine days earlier, on the sixth, both traditions keep the Transfiguration, the revelation of Christ's glory on the mountain, a summer feast on which Orthodox custom blesses the first grapes of the year.
August opens with the firstfruits. Lughnasadh, the Gaelic festival of the first of August, was the funeral games the god Lugh founded for his foster mother Tailtiu, and its Christianised English double is Lammas, the loaf mass, when bread baked from the first of the new wheat was brought to church. Modern Pagans keep the day as the first of the three harvest stations of the Wheel of the Year.
In Japan the middle of August is Obon, when the spirits of the ancestors are welcomed home with lanterns, fed and entertained with the circling bon odori dances, and sent back across the water with floating lights. The related Hungry Ghost Festival of the Chinese seventh lunar month falls in August in most years, another feast in which the living owe the dead hospitality at the summer's turning.
Sources The Oxford Dictionary of the Christian Church, 3rd revised editionF. L. Cross and E. A. Livingstone (eds.) with Celtic Culture: A Historical EncyclopediaJohn T. Koch (ed.), Buddhas and Kami in Japan: Honji Suijaku as a Combinatory ParadigmMark Teeuwen and Fabio Rambelli (eds)