The Sharad Purnima or Kojaagari Purnima or Kumar Purnima is a harvest festival celebrated on the full moon day of the Hindu lunar month of Ashvin (September–October). It marks the end of monsoon. There is a traditional celebration of the moon and is also called the 'Kaumudi celebration', Kaumudi meaning moonlight.
It is also believed that on this day as moon and the earth are very close to each other, the moon rays have certain healing properties of nourishing the body and the soul.
At night, goddess Lakshmi is worshiped and night vigil is observed. According to a folk-tale, once a king fell on evil days, and was in great financial difficulties, but then his queen observed this fast and night vigil, and worshiped the goddess of wealth, Laxmi. Consequently, they were blessed by the goddess and they regained their prosperity.
Some people believe that on this night, goddess Laxmi goes around from place to place asking Ko jaagariti ( means – who is awake?) and shows her pleasure on those she finds awake. Hence, the night is spent in festivity and various games of amusement, in honour of the goddess. People sit in the moonlight singing songs, or keep themselves entertained in some other way. They observe fast and take only fluids like coconut water or milk. There is also a tradition to have cool milk and rice flakes (Poha) on this night.
According to one legend in the Sanatkumar Samhita, rishi narrates that in ancient times, a poor Brahmin named Valit lived in Magadhdesh - Bengal. While he was a learned and virtuous man, his wife reveled in quarrelling and behaving totally opposite to his wishes. Once on his father's `Shraddh' - day of paying homage to the deceased- she flung the 'pind' - ball of wheatflour - in a sewage pit, instead of the sacred Ganga, as per customs. This infuriated Valit and he renounced home to search for wealth. In the forests, he met 'Naagkanyas' - girls of Kaliya Naag's ancestry. These Naagkanyas had performed the 'Kojaagari Vrat' - staying awake. They then sat gambling with Valit. The night happened to be Aso sud Purnima. Valit lost everything. At that moment, Lord Vishnu and Lakshmi, happened to pass by. Since Valit had incidentally observed the 'Kojaagari vrat', Lakshmi graced him handsomeness similar to that of 'Kamdeva' - the deity of love. Attracted to him, the Naagkanyas married Valit and gave him their riches. He then returned home with the riches, where his wife received him warmly. After this episode, the Samhita declared that those who remain awake on this Purnima will be graced with wealth.
Another legend has it that on this night, Lord Krishna invited His faithful devotees, the Gopis of Vrundavan, to play the Maha Raas with Him. They had earned His grace by overlooking society's disdain on them (`loklaaj'), to offer Him unalloyed devotion. When they left their homes in Vraj and arrived in Vrundavan, Shri Krishna welcomed them. To further test their love for him, He commented: 'Women of character such as you, should not leave home to meet another man in the middle of the night!' These words seared the Gopis' hearts. In extreme grief, they uttered: 'Our feet will not budge the slightest from Your lotus-feet. So how can we return to Vraj?' Pleased with such devotional love for Him, Shri Krishna initiated the Maha Raas, by assuming as many forms as there were Gopis. At this point, they beamed with pride that, 'Nobody's devotion can excel ours, by which the Lord favored us.' Instead of accepting the Maha Raas as the Lord's grace, ego marred their devotion. Therefore He instantly vanished from the Raas mandal. Now filled with remorse, the Gopis repented. They lamented the separation and sang kirtans known as 'viraha geet': 'Jayati te-dhikam janmanaa vrajaha ….. (Shrimad Bhagvat 10/31/1) .
It is a harvest festival and is celebrated throughout the country, particularly in Maharashtra and Gujarat. In Gujarat, the night is known as Sharad Poonam. And is celebrated by doing Garba and Raas. In Bengal, people call it Lokkhi Pujo and arrange several bhog and upachar for mother goddess Lakshmi. In the Mithila region, the puja is known by the name of Kojagaraha. It is celebrated in all Maithil households.
There is an Ayurvedic reason behind consuming rice flakes with cool milk on this night. Sharad ritu (season) consists of two months of overlapping seasons when the summer is about to end and the winter slowly starts. During Sharad the days are warm and nights start to become cooler. This is perfect season for Pitta prakop when pitta vitiates along with other two doshas. Consuming rice flakes with milk during night time is good remedy to pacify pitta.
Symbolically speaking, just as the night sky of Sharad Punam is clear and suffused with lunar resplendence, one should similarly endeavor to purify his 'antahkaran.' For this he has to eradicate body-consciousness and mundane desires and imbibe Brahma-consciousness, in order to incessantly experience Parabrahma. (Gita 18/54, Shikshapatri 116).