Sharad Purnima is celebrated on Shukla Paksha Purnima of Ashwin Month as per hindu calendar. This day carries special significance in the land of Mathura & Vrindavan because on this day Lord Krishna is considered to have performed Maharaas Lila with his beloved gopis and Radha together by holding multiple forms to please them all .
Maharaas lila performed by Krishna and Gopis of Vrindavan on Sharad Purnima is considered as epitome of love between Krishna and his devotees as Krishna fulfilled the desire of Gopis by dancing with each of them separately and together at the same time by having multiple form.
As per the hindu scriptures the reason of performing Maharaas by Krishna was to fulfill the commitment made by him to his many devotees in his different incarnations (Lord Krishna is also an incarnation of God Vishnu).
There are many legends related to the event of Maharaas in Vrindavan. One of them is about Lord Shiva.
As per the legend, when shri Krishna started playing his flute in the beginning of Raas leela, Lord Shiva got attracted to the sound of flute and went himself to find the source of flute music, when he reached vrindavan and was about to enter in the Maharaas, suddenly he was stopped vrinda devi at the gate and was refused entry as vrinda devi said that only gopis are allowed to enter there. Then lord shiva disguised himself as gopi and got the entry, but still he was recognized by Krishna who laughed and fulfilled his wish to play raas with him. Since then Lord shiva is known as Gopeshwara Mahadev and there is an ancient temple in vrindavan in the honor of Lord Gopeshwara Mahadev.
On this day Raasleela is performed by devotees of Krishna in various temples of Mathura & Vrindavan. In Banke Bihariji Temple, Vrindavan on this Lord Krishna’s murli ( his flute ) is kept in between his hand & lips ( all the other days of year , flute of Krishna is kept beside Krishna in this temple ), so it is a rare occasion in Banke Bihari Temple.
This year Sharad Purnima will be celebrated on Tuesday, October 7, 2014.