01What Guru Purnima is
Guru Purnima is the Purnima of Ashadha, the full moon at the start of the monsoon, given to the guru: the teacher who passes on knowledge, and in the fuller sense the tradition gives the word, the one who leads a student out of darkness into understanding. It is also called Vyasa Purnima. Students honour their teachers, disciples their spiritual guides, and musicians and dancers the gurus of their lineage. Because the four months of Chaturmas begin around it, many monastic orders mark the day as the start of their rainy season retreat, when wandering stops and teaching begins.
02The story told of it
The tradition names the day for Veda Vyasa, the sage it credits with arranging the Veda into four, composing the Mahabharata and setting down the Puranas, and holds that he was born on this full moon. To honour Vyasa is to honour the first teacher of the whole line through which those texts reached every later guru. Other traditions keep the same full moon for their own beginnings: Buddhists remember it as the day the Buddha gave his first teaching at Sarnath, and Jains as the day Mahavira received Gautama Swami as his first disciple.
03How it is kept
The heart of the day is guru puja: the disciple washes or touches the feet of the teacher, offers flowers, fruit, cloth or dakshina, and asks for blessing. Where the guru cannot be met in person, the worship is made before a picture or the padukas, the sandals. Ashrams hold readings, satsang and bhandara, and many people read from the Gita or the Guru Gita. Schools of music and dance in the guru-shishya line keep it as their own day. Some fast until the puja and then share the prasad, and many simply visit a teacher they owe something to and say so.
04How the day is chosen
It is kept on the day its tithi is current at sunrise in your city.
05Guru Purnima in other years