What is Krishna Janmashtmi and why is it celebrated?

According to the Puranas, Kansa was an evil king of Mathura who had overthrown his father and imprisoned him. His atrocities drove the gods to Vishnu who promised to take his eighth incarnation in the human world. He was then born as Krishna in the 28th year of the Dwapara Yuga. Vishnu took his eighth incarnation of Krishna to kill the evil king Kansa. As per the legend related to Krishna's birth, Kansa had a cousin called Devaki, whom he loved dearly. In due course, Kansa arranged a suitable match for her and married her with great pomp and show. However, an oracle foretold Kansa that Devaki's eighth child would be responsible for his death. Enraged, Kansa was about to slice off her head when her husband Vasudeva intervened.

He begged Kansa not to kill Devaki and in return promised to give him all their children at birth. Kansa agreed, but imprisoned the couple to ensure this. In time, he killed six of their children by throwing them against a stone slab outside the prison. The seventh child however was transferred to the womb of Rohini; another of Vasudeva's wives, and Kansa believed that Devaki had suffered a miscarriage. When she was pregnant with the eighth child, Kansa increased security at the prison and ordered the guards to bring the newborn to him the moment he was born.

At midnight on the eighth day in the month of Shravana, on a dark, rainy and windy night, just before the child was born, the guards all fell into a deep slumber and the locks on the prison door opened. Devaki and Vasudeva too were freed of their binds and Krishna was born. A voice from the heavens instructed Vasudeva to carry Krishna across the Yamuna River to a village called Gokul. There, he should go to the home of his sister Yashoda and her husband Nanda and replace Krishna with their newborn daughter. Vasudeva put his son in a basket and went quickly towards the Yamuna. When he reached the shores, he found the water level rising. He put the basket on his head and began towards the Yamuna. The water level rose but every time it touched the baby's toes, it receded. Suddenly, a cobra sprang out of the water. Vasudeva froze but the snake stopped to spread its hood over the basket. It was Sesha Naga protecting Krishna from the rain. Vasudeva realized his son was no ordinary baby. He hurried to Gokul, exchanged the children and returned to the prison.

As soon as he entered, the locks shut and the guards awoke. Hearing the baby cry, they informed Kansa who rushed to the prison. He was about to smash the little girl against the stone slab, when she slipped out of his hands. As she rose towards the sky, she warned him that the one responsible for his death was safe. When Krishna grew up, he killed his evil uncle and restored the throne to his grandfather.

The day of the birth of Lord Krishna is very popular in north India. People observe fast all day long, which is broken only at mid night, the time when Krishna is believed to have born. The festival is a community celebration, and people visit Krishna temples, which are specially decorated and lit for the occasion.