Shivratri is celebrated a night before ‘amavasya’ (full dark night) in the month of Phalgun (February – March) in North India. As per traditional calendars followed in Gujarat, Andhra Pradesh, Karnataka and Maharashtra this is the Magh Krishna Paksha Chaturdasi. The significance of Shivaratri is closely associated with ‘amavasya.’ Amavasya represents Kaliyuga. Lord Shiva appeared just before the beginning of Kaliyuga to rid the world of evil and ignorance, which is symbolically represented through Amavasya. Therefore Mahashivratri is celebrated to get rid of evil and ignorance.
On the Shivratri day, Lord Shiva is worshiped in a special form of Linga called ‘Lingodabhavamurti or Jyotirlinga.’ It is a lingam in the form of fire which has neither a beginning nor an end. It must be noted here that ‘linga’ only means ‘sign.’ And it is merely an attempt to capture the formless.
Apart from this there are numerous legends and myths associated with Shivratri. An important myth is that Shivaratri is the birthday of Lord Shiva – this is mainly because the formless Lord Shiva appeared for the first time in the form of ‘Lingodabhavamurti’ before Lord Vishnu and Brahma.