Maha Shivaratri (01/03)

On the 14th day of Chaturdashi Krishna Paksha in the dark fortnight of the month of Maga, the Great Night of Lord Shiva, Maha Shivaratri, is celebrated.

Hindu scriptures, in particular the Skanda Purana, describe four types of Shivaratri:

The first is Nitya Shivaratri (daily Shivaratri - every night). The second is Masa Shivaratri (monthly Shivaratri), which is observed on the fourteenth lunar day (Chaturdashi) of the waning moon (Krishna Pakshi).