Krishna’s avatara day is celebrated as Sri Krishna Jayanthi. The word ‘jayanthi’ has a special significance. It is not a reference to one’s birthday. It is a word to be used exclusively for Krishna’s time of birth, because He was born at a very special time, said M.A. Venkatakrishnan in a discourse.
Krishna was born in an auspicious muhurtha, with a rare combination of factors. Krishna was born in the month of Sraavana, in Ashtami tithi, in the star Rohini, and the time of birth was midnight. This muhurtha is called Jayanthi. This coming together of various factors at a particular time is called Jayanthi. Since Krishna was born in the muhurtha known as Jayanthi, His avatara day is celebrated as Sri Krishna Jayanthi. Jayanthi does not mean birth. It is the name of the very special muhurtha in which Krishna was born.
It was such a good muhurtha that it would cause even poison to turn into nectar! And we see this in the life of Krishna. Putana tried to kill Him through her poisoned milk, but Krishna remained unharmed, and it was she who paid with her life for her wicked attempt. Rama was born in a palace, while Krishna was born in a jail. Rama was born in day time, while Krishna was born in the night. Rama was born in the month of Chaitra, when the season was spring (Vasantha rtu). Krishna was born during the monsoon season (Varsha rtu).
We offer simple fare to Rama on His avatara day. But for Krishna, the offerings are rich and varied. In Melkote, thirty types of delicacies are offered to the Lord on Sri Krishna Jayanthi. The reason for the difference in grandeur between the two celebrations is perhaps because Rama, as a prince, had the best of everything. But Krishna never had such luxuries, and so grand celebrations for Him become justified.