Hunnime or Poornima is the day of Full moon, And the full moon night of Sharad ritu (season) is Sharad Purnima. It officially marks beginning of the Winter Season and end of Monsoon (rain).
It is believed that the Pious dance, Raas by Radha and Krishna took place with Gopis on this night (and Sharad Poornima is also referred to as Raas Purnima). It is also the only day in the entire year when Moon has all the 16 Kalas
Reproducing part of talk by Pujya Gurudev Sri Sri Ravi Shankar ji of The Art of Living on the significance of Kala.
Kala usually refers to the extent by which the moon waxes (or wanes) in one day. Moon possesses 16 different Kalas (different phases of the Moon). You can observe this from one Amavasya(No-moon day) to the next Purnima (Full moon day). So if you count the number of days from one Amavasya to the next Purnima, it turns out to be 16. And the transition from No-Moon to the Full Moon also symbolizes moving from Zero (nothingness) to Fullness.
Kala is a unit of measure of one’s power, or by what degree one has blossomed or progressed. So, someone may be like a half-moon, someone else may have reached to three quarters of the moon and so on. This was a means of measurement in the ancient days.
In those days, it was said that the life or Prana in a stone is equal to one Kala, the water element is said to have two Kalas. Fire has three Kalas, Vayu (Air element) has four, and the Space or Akash has five. Plants and trees are said to have six Kalas. Animals have seven Kalas. Human beings have eight Kalas.
If it is an extraordinary human being then he is said to have nine Kalas. It is said that Lord Parashurama (one of the ten avatars of Lord Vishnu) had nine Kalas. They say Lord Rama has 12 Kalas. Lord Hanuman is greater than Him in this regard and is said to have 14 Kalas. That is why he could help Lord Rama. Only a person who is stronger than us can help us.
The Devi (Mother Divine) is called Shodashakala (The One with all 16 Divine qualities or attributes). It means that she possess all divine and noble qualities, and lacks nothing.
Lord Krishna too is said to have all 16 Kalas, which is why He is called as the Solah Kala sampurna or the Purna Avataar.
To have all 16 Kalas means to possess all the 16 qualities or signs attributed to the total blossoming and manifestation of Divinity.
On the day when moon has all 16 Kalas it is believed that its rays has special and healing effects on humans. Since each of the 16 Kalas signify 16 qualities, exposing ourselves after due preparation of our mind and body, makes us a perfect human being. Some also believe that it is the night when Moon emits Amrutha (Elixir). Moon is at closest distance tonight and hence will be the brightest
Typically a vrat is observed on the day preceding the Full moon night and Goddess Lakshmi comes in search of those who are awake (and hence called Kojagiri Purnima). Being awake is not just about not sleeping but being spiritually awake for which Upavasa, Meditation and Jagarane is observed. Devotees stay awake engaged in prayers, singing and dancing (Raas) so that Goddess Lakshmi finds them awake and blesses them in Abundance.
An important thing to note, though it is dedicated to Divine couples, Radha-Krishna, Lakshmi-Narayana or Shiva-Parvati – umarried ones observe this day to get a good spouse and married ones for longevity of the spouse, the first puja is offered to Bhagwan Surya early in the morning and then begin the vrata and to end the same with worship of the Moon.
On this day, all food items made as prasad is predominantly of White color – what we prepare is Coconut Rice (not the Sanjeev Kapoor types, but typical and real South Indian Coconut Rice), Milk Payasa, Curd Rice, Cobbari Mithai (Coconut Burfi) and all of us go to the terrace (weather permitting) and dine under the moon. We also wear white dress for the night, sing a few Bhajans and do what I like the most – have prasada.
Some regions leave all these overnight in the moon and have it as prasada in the morning.
Here is wishing all the readers a Happy Sharad Hunnime or Sharad Purnima. May Goddess Lakshmi bestow Her choicest blessings on you and all your near ones. Prayers that all unmarried looking for a partner to be blessed with a great one and those married for long, blissful journey of togetherness.