Vyasa-puja is an annual celebration by the devotees of Lord Krishna to offer homage to their guru, or spiritual master. Vyasa-puja means “worship of Vyasa,” Vyasa being the compiler of the Vedic scriptures and thus the original spiritual master.
The ceremony takes place on the spiritual master’s appearance day (a respectful term for “birthday”). Disciples honor their guru because he authentically transmits the teachings of Vyasa.
Although the International Society for Krishna Consciousness has many spiritual masters, or acaryas, Srila Prabhupada, its founder-Acharya, holds a permanent position of special esteem. So just as when he was physically present (1965 through 1977), each year his disciples and followers gather on his appearance day to praise him and recall his glories.
The celebration falls in late August or early September, the day after Sri Krishna Janmashtami, the appearance day of Lord Krishna. The day is calculated according to the lunar calendar, so it differs every year.