Buddha Day is also known as Vesak Day [Hanamatsuri (花祭)], or Teacher’s Day. Buddhists celebrate today as the Buddha’s (Shakyamuni) Birthday. It is considered by most to be the most important day in Buddhism and most Buddhists spend the day in contemplation of the Buddha’s life and enlightenment. Celebrations outside the temples often involve ceremonial bird releases and some local traditions or culture into the festivities.
Celebrations at the temples often involve guest speakers as well as chanting and praying and offerings to the Buddha statue (usually vegetarian in line with Buddhist beliefs) in respect for his life and teachings.
In many east Asian countries Buddha's Birth is celebrated on the 8th day of the 4th month in the Chinese lunar calendar (in Japan since 1873 on April 8 of the Gregorian calendar), and the day is an official holiday in Hong Kong, Macau, and South Korea. The date falls from the end of April to the end of May in the Gregorian calendar.
As a result of the Meiji Restoration, Japan adopted the Gregorian calendar in lieu of the Chinese lunar calendar in 1873. In many Japanese temples, Buddha's birth is celebrated according to the Gregorian calendar dates, and rarely on the orthodox Chinese calendar dates.
In Japan, Buddha's birth is also celebrated according to the Buddhist calendar but is not a national holiday. On this day, all temples hold Kanbutsu-e (Japanese: 灌仏会), 降誕会 (Gōtan-e), 仏生会 (Busshō-e), 浴仏会 (Yokubutsu-e), 龍華会 (Ryūge-e), 花会式 (Hana-eshiki) or 花祭(Hana-matsuri, meaning 'Flower Festival'). The first event was held at Asuka-dera in 606. Japanese people pour ama-cha (a beverage prepared from a variety of hydrangea) on small Buddha statues decorated with flowers, as if bathing a newborn baby.