The birthday of Lord Krishna, the eighth incarnation of Lord Vishnu, is celebrated as Janmastami. It falls on the eighth day of the dark half of the month of Bhadraba. Of all the divine incarnations of the God, Sri Krishna is the most adored. By virtue of His divine Leelas or sports, Krishna has become the darling of the humanity.
The purpose of taking this avatar or incarnation was, as explained in the Bhagavat Geeta, the annihilation of evil and the establishment of truth and virtue. As such, from His infancy onwards Krishna destroyed numerous demons (suggestive of evil forces) who were harassing the Gods and men alike. Later, as an ally of the pandavas, He brought about in the interest of truth and justice, the war of Kurukshetra to destroy the wicked Kauravas and restore legitimate rights to the honest and truthful Pandavas.
It was from this battle field that He delivered His Message to the suffering humanity which has come down to us as the most sacred book 'Geeta'. All His sports or Leela have been elaborately described in the Bhagavata, Mahabharata, HariJanma and many other religious texts. The birth day of the Lord is, therefore, celebrated as one of the greatest of all Hindu festivals in all houses.
Lord Krishna was born at mid-night when the moon entered the house of Vrisabha at the constellation of the star Rohini on the eighth day of the dark half of the month of Bhadrab. Therefore, it became customary to observe fasting upto mid-night till the exact hour of birth. When the fixed hour comes conches are blown, gongs are sounded, slogans involving the God are given which heralds the birth of Krishna. After this Bhog (food offering) is offered to the deity and the fast is broken. The festival is widely celebrated in all vaishnavite temples, monasteries and houses. Clay images of Krishna are also worshipped on this occasion. The festival is devoutly observed by the cowherd community of Orissa, as Krishna lived and spent his childhood days in Gopa. The next day is observed as 'Nandotshaba' by this particular community as a reminiscence of the festival that was held by Nanda Raja, to celebrate the birth and arrival of Krishna. The young boys sing songs related to Krishna's sport and dance to the beats of resonant sticks.
While vaishnavism was the court-religion of Orissa since 11th century A.D., the cult of Krishna worship was made popular during 15th century A.D. by Shri. Chaitanya and his followers. Though temples exclusively dedicated to Krishna are few in Orissa, the representative deities at Lord Jagannath are no other than Krishna who is known as Madana Mohana, Ramakrishna, Gopala, Gopinath etc.