Some 5000 years ago, Krishna appeared on the midnight the eight day of waning moon (Ashtami tithi under Rohini Nakshatra) as the eight son of Devaki and Vasudev in Mathura district of Uttar Pradesh, India.
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On this day devotees fast till mid-night and observe Janmashtami vrata and seek His blessings

janma karma ca me divyam evam yo vetti tattvatah

The Lord’s appearance is not like that of an ordinary man, who is forced to accept a material body. He appears out of His own sweet will.
Lord Krishna is all-attractive, all-auspicious and all-blissful, and so are His pastimes, which are completely beyond the imperfections and contaminations of the material world and activities.