Shivaratri is celebrated on Krishna Paksha Chaturdasi of the Maaagha month. On this day Lord Shiva is worshipped throughout the night and a fast is also observed the entire day. There are many legends entwined with Shivaratri. Lord Brahma
and Lord Vishnu fought between themselves to determine who was the greatest. To stop them Lord Shiva
appeared between them as a pillar of fire. The gods were not able to find the starting and end of that pillar. When Brahma and Vishnu repented their mistake and prayed to Lord Shiva to forgive their sin then he appeared before them and blessed them on the night of Shivaratri.
During the Samudra Manthan between the gods and demons a poison came up which was so toxic that it had the ability to wipe out the whole creation. Lord Vishnu advised the Gods to pray to Lord Shiva. Lord Shiva was pleased by the prayer and drank the poison to hold it in his neck. His throat became blue due to the poison and he was known as `Nilakantha`, who was the protector of the world. This is also a legend behind following Shivaratri.
In another story, during deluge, the whole world was facing destruction. Goddess Parvati prayed to Lord Shiva to save the living beings that were living in space as particles of gold dust in a lump of wax. He granted the prayer of Parvati and the Jivas became active again. After the deluge stopped and creation was complete, Parvati asked Shiva which rituals pleased him most. Lord answered the thirteenth night of new moon in the month of Magha was his most favorite day.
Another legend says that in a Shiva temple on Shivaratri day the lamp kept on the altar was dim. That time a mouse was running after its prey. It touched the flame and due to heat it removed its head very quickly. In this process the mouse kindled the lamp brightly and the altar was well illuminated. Lord Shiva was very pleased and blessed him and made it Mahabali, the renowned Asura king.
In the Shanti Parva of Mahabharata
while lying on the bed of arrows gave reference to this story. The King Chitrabhanu of the Ikshvaku Dynasty, ruled over the whole of Jambudvipa, was observing fasting on the day of Shivaratri along with his wife. The sage Astravakra visits him and wanted to know the reason. The King explained that he has a gift to remember his previous birth. On his previous birth he was a hunter in Varanasi
named Suswara who earned his living by killing and selling birds and animals. One day while roaming through the forest for his prey, he could not kill a single animal. He had let a deer to live after seeing the deer`s sad family. Overtaken by the darkness of night and unable to return home, the hunter climbed a tree nearby, which was a Bel tree. He could not sleep throughout the night as he was thinking about his fasting wife and children. He did not eat or drink anything. The hunter engaged himself in plucking the Bel leaves and dropped them on the ground.
The next day when the hunter returned home he bought some food for his family. But the moment he was about to break his fast, a stranger came to him, begging for the food. He served the food first to the stranger and then took his own part. At the time of death the hunter saw two messengers of Lord Shiva, who took his soul to the abode of Shiva. There was a Shiva Lingam under the Bel tree, which he climbed and he washed the Lingam with water from his canteen and dropped the Bel leaves. Unknowingly he was fasting all day and all night. Therefore, he got the divine bliss of Lord Shiva, living in his abode for a long time and was reborn as a King.
Cold water and Bel leaves are offered to the Shiva Lingam. Other offerings include milk, curd, ghee, sugar and honey. On this day he is worshipped as deity of dissolution.