Sharad Poornimaa is celebrated on Aashwin Poornimaa. It is believed that on this night the Moon showers the cool nectar of peace along with the eternal nourishing power on the earth.  It makes the mind peaceful and reduces the effect of ‘Pitta, one should acquire this important moonlight on this night.

Ved Vyaas Jee has described the night of ‘Sharad Poornimaa’ as the night of the Raasotsav (Raas celebrations) of the incarnation of Krishn on the Earth in Bhaagvat Puraan's 10th Skandh, , because unlike the Moon showering the cool nectar Krishn too, showered ‘Bhakti Ras' on the Earth. This day is celebrated with full enthusiasm in Brij.

It is also believed to be the day of manifestation of Swaamee Kaarttikeya.

On this day Pohaa (Chivadaa, or puffed rice, or beaten rice, or parched rice) made from new rice along with Kheer, are prepared and left in the moonlight between 9 pm and 12 pm for overnight and then are eaten the next morning. Gold ornaments are also placed in the pot in which the Kheer is cooked. One should never add raisins in any of the milk preparations, though cashew nuts and Charoli (Chiraunjee) can be added. The Prasaad thus prepared should be taken after the Satsang and performing Poojaa, Jap, Dhyaan with the feeling of gaining good health, self cool and prosperity.

White puffed rice, white milk, white sugar and also the moonlight being all white in color…. hence this occasion can also be called "Dhawal Utsav" where Dhaval means white.

The Moon is at the closest point to the Earth on this day and its bright rays have their own curative properties. The rays fall on the food or drinks that are consumed, and help in curing the disorder of Pitta and avoid many other trivial diseases and makes the body healthy.

As the Lord says :
Pushnaami Cha Aushadhi : Sarvaa Somo Bhootwaa Rasaatmak
I provide strength to the medicines in the form of Moon.

Moon represents calmness in the spiritual form, It is not that there were no problems in the life of Krishn, in fact the Lord faced problems from the very moment of His birth. Raam enjoyed only pleasures in life…  this is also untrue, He was exiled at the time of his coronation, but still he was calm, and did not lose His patience.

Sharad Poornimaa is also known as "Kojaagaree Poonam", the festival is celebrated on Asauj (Aashwin) Shuddh 15 - Poornimaa. Lakshmee, the goddess of wealth moves around in the night sky, asking "Ko jaagrati", searching for people below who are awake. "Ko jaagarti" means, ‘"Who is awake?" And to those who are awake she gifts wealth.

Origin of the Festival:
(1) The Sanatkumaar Sanhitaa cites the story of "Kojaagari Poonam". In the Sanhitaa, Baalkhilyaadi Rishi narrates that in ancient times, a poor Braahman named Valit lived in Magadh Desh - Bangaal. While he was a learned and virtuous man, his wife reveled in quarreling, behaving totally opposite to his wishes. Once on his father’s Shraaddh, she flung the Pind - ball of wheat flour - in a sewage pit, rather than the sacred Gangaa, as custom required. This infuriated Valit. Therefore he renounced home to search for wealth. In the forests, he met some Naag Kanyaa (girls of Kaaliya Naag’s ancestry). These Naag Kanyaa had performed the Kojaagaree Vrat - staying awake on Asauj Shuddh Poonam. They then sat gambling with Valit. Valit lost everything. At that moment, Vishnu and His consort Lakshmee, happened to pass by. Since Valit had incidentally observed the Kojaagaree Vrat, Lakshmee Jee graced him handsomeness similar to that of Kaam Dev - the deity of love. Now attracted to him, the Naag Kanyaa married Valit and gifted him their riches. He then returned home with the riches, whence his wife received him warmly. After this episode, the Sanhita declared that those who remain awake on this Poonam will be graced with wealth.

(2) On this night, Krishn invited his faithful devotees, the Gopee of Vrindaa Van, to play the Mahaa Raas (traditional folk-dance) with Him. They had earned his grace by overlooking society’s disdain on them (Lok Laaj), to offer Him unalloyed devotion. Pleased with such immutable love for Him, Krishn initiated the Mahaa Raas, by assuming as many forms as there were Gopee.

Jayati te-dhikam janmanaa vrajah ….. (Bhaagvat Puraan, 10/31/1)
Describing the "Leelaa" in the Bhaagvat (10/30/25), Shuk Dev Jee narrates to king Pareekshit: "O Parikshit, Of all nights, that night of Sharad Poonam became the most resplendent. With the Gopee, Krishn roamed the banks of the Yamunaa, as if imprisoning everyone in his Leelaa.

One should remain vigilant at the gateway to God, not letting any mundane objects through. Every moment in our lives requires vigilance and this in itself becomes a subtle form of Tapas - austerity. Those who performed severe austerities without vigilance, succumbed to Maayaa. Vishwaamitra performed austerities for 60,000 years, but lost Jaagriti - vigilance - in Menakaa’s company. Similarly, lack of vigilance toppled Saubhari Rishi, Shringee, Paraashar and others too.

Just as the night sky of Sharad Poornimaa is clear and suffused with lunar resplendence, the aspirant should similarly endeavor to purify his Antahkaran. For this he has to eradicate body-consciousness and mundane desires and imbibe Brahm-consciousness, in order to incessantly experience Par-Brahm. (Geetaa 18/54, Shikshapatri 116). For this the aspirant needs to seek the Gunaateet Saadhu, who is the gateway to Moksh (the Lord), as proclaimed in the Bhaagvat (3/29/20):

Means, the sages decree that if a Jeev who is deeply attached to his body and bodily relatives, if similarly attaches himself to the Gunaateet Saadhu, the doors of Moksh will be opened for him.