Once when everything, in all the worlds was withdrawn into Lord Shiva and and in that darkness of dissolution, the Divine Mother Parvati worshipped Lord Shiva as laid down by the Agamas. Parameshwara, pleased, blessed Her with a boon. So that all creatures may benefit in future, She asked that going forward whoever worships the Lord on the day of Shivaratri with devotion, be blessed with ultimate liberation. Pashupati granted it thus paving the way for all of us to get blessed easily.
When Brahma and Vishnu were engaged in battle between themselves as to who the greatest was, Lord Shiva appeared before them as an infinite column of fire. The day that the column of fire appeared is celebrated as – Tiru-Kartikai. Brahma and Mahavishnu were not able to find the start or end of that column. They repented their folly and prayed to Lord Shiva for forgiveness. The night when Lord Shiva appeared before them from the column of fire as a shiva-linga that they can worship and blessed them came to be known as Shivaratri. For this reason the midnight of Shivaratri is hailed as the Lingodbhava Kala.
இவ்விரதம் ஆண்டுதோறும் மாசி மாதத்தில் வரும் கிருஷ்ணபட்ச (தேய்பிறை) சதுர்த்தசி திதியில் இரவில் கொண்டாடப்படும்.