the-indian-way:

Maha Shivaratri is a Hindu festival celebrated in reverence of God Shiva. 

As per Hindu mythology, this day is believed to be the day when Shiva saved the universe by drinking the poison emerged from the churning of the ocean (samudra manthana). 

It is also believed to be the day in which Shiva married Goddess Parvati (Shakti), and the night he performed the Tandav, the cosmic dance.

While most Hindu festivals are celebrated during the day, Maha Shivaratri is celebrated during the night, by keeping a jagaran - a night-long vigil, (as it is believed that Lord Shiva saved the universe from darkness and ignorance). 

The festival is principally celebrated by Shiva lingam puja, offerings of bael leaves to Shiva, as well as water, milk and honey, all-day fasting and an all-night-vigil. 

All through the day, devotees chant Om Namah Shivaya, the sacred mantra of Shiva.