Maha Shivaratri is celebrated over three or ten days based on the Hindu luni-solar calendar. Every lunar month, there is a Shivaratri (12 per year). The main festival is called Maha Shivaratri, or great Shivaratri, and this is on 13th night (waning moon) and 14th day of the month Phalguna (Magha).
The festival is celebrated on the new moon day in the month of Maagha according to the Hindu calendar. The day is celebrated to venerate Lord Shiva, an important deity in Hindu culture. ... From that day onwards, the night came to be known as Maha Shivratri and people began worshipping Shiva with a great enthusiasm.
Maha Shivaratri is an annual festival dedicated to the Hindu god Shiva, and is particularly important in the Shaivism tradition of Hinduism. Unlike most Hindu festivals which are celebrated during the day, the Maha Shivaratri is celebrated at night.