That is why this festival that celebrates the birth of Shri Krishna is called Janamashtmi.
An Auspicious Day:
Lord Krishna was born in the “Rohini” Nakshatra (star), which is considered to be very auspicious as it is supervised by Lord Brahma.
The celebration of Janmashtami lasts for two days, as it was midnight when Lord Krishna was born. The First day is called “Krishnashtmi” and the Second day “Kalashtmi”.
There are also times when Ashtmi and the Rohimi Nakshtra don’t conspire on the same day.

Environment of happiness:
Krishna’s birth is synonymous with happiness and joy as, when Devaki was about to give birth to Krishna her face radiated and all walls of the prison lighted up, rivers were swollen up with water and all birds and animals were chirping and rejoicing.
To feel the same happiness Krishna’s devotees all over the world, are awake throughout the night and chant mantras with a belief that it will fall on Krishna’s ears.