Janmashtami is celebrated as Lord Krishna's birthday. Born in the king's prison on the eighth day of the dark fortnight of the month of Bhadrapada in Mathura, the city of Kamsa, the demon king, Lord Krishna was the eighth child of Devaki. It was midnight and the moon was rising when Rohini Nakshatra was born. Therefore, Krishnashtami celebrates Lord Krishna's birthday every year.

Krishna Janmashtami Muhurat
1 If Ashtami gains the upper hand at midnight, Vrat must be kept for the next day as well.
2. If Ashtamity continues to midnight on his second day, fasting must be done on his second day.
3. If Ashtami predominates until midnight on his two days, and Rohini nakshatra predominates only for one night, the day following that night must be regarded as fasting.
4. If Ashtami prevails until midnight for two days and there is Rohini Nakshatra on both nights, Krishna Janmashtami fasts on the second day.
5. Krishnajayanti fasts on his second day when Ashtami prevails until midnight on his two days and there is no Rohini nakshatra day.
If Ashtami Titi is not prevalent at midnight on these two days, fast on the second day.

Note: The above Mukhrat is given according to Smarthas. Vaishnavas celebrates his Gokulashtami on his second day. Smarthas and Vaishnavas have different views on celebrating this festival.

According to Hindu scriptures, Vaishnava are those who have been initiated by the Vaishnava community. These people usually wear a small rosary made of sacred beads and place a tilak symbolizing Vishnu's feet on their foreheads. Except for these Vaishnava people, all others are considered smarthas. In other words, those who are not initiated by the Vaishnava community are called Smartas.