Why is it celebrated?
Maha Shivaratri is celebrated with great devotion and religious fervor by Hindus, in honor of Lord Shiva, one of the Hindu Gods forming the Trinity.
The many stories for the reason of celebration of this festival are below:
1) According to one of the most popular legends, Shivaratri is the wedding day of Lord Shiva and Parvati. It is also believed that Lord Shiva performed ‘Tandava’, the dance of the primal creation, preservation and destruction on this auspicious night of Shivaratri.
2) According to another popular legend, described in Linga Purana, it was on Shivaratri that Lord Shiva manifested himself in the form of a Linga for the first time. Since then, the day is considered to be extremely auspicious by the devotees of Shiva and they celebrate it as Maha Shivaratri - the grand night of Shiva
3)One of the most popular tales traces its origins to samudra manthan, or churning of the ocean of milk. According to this belief, when the gods and demons were churning the ocean of milk to obtain amrita (drink of immorality), they came across many unusual substances including a deadly poison. Terrified, the gods approached Shiva for help, and out of compassion for all living beings, Shiva swallowed the poison. The poison was so potent that it turned his neck to blue
4) According to a legend, Parvati performed tapas, prayed and meditated on this day to ward off any evil that might befall her husband on the moonless night. Since then, Mahashivaratri is believed to be an auspicious occasion for women to pray for the well-being of their husbands and sons. An unmarried woman prays for a husband like Shiva, who is considered to be the ideal husband
5) Another version relates that the whole world was facing destruction and Goddess Parvati worshipped her husband Shiva to save it. She prayed for the jivs (living souls) remaining in se – like particles of gold dust in a lump of wax -- during the long period of pralaya (deluge) night, that they should, upon becoming active again, have His blessings, but only if they worshipped Him just as she did. Her prayer was granted. Parvati named the night for the worship of Ishwar by mortals Maha-Sivaratri, or the great night of Shiva, since Pralaya is brought about by Him
[Src: http://en.wikipedia.org/wiki/Maha_Shivaratri ]
When is it celebrated?
The festival falls on the moonless, 14th night of the new moon in the Hindu month of Phalgun (in the month of February - March, according to English Calendar).
How is it celebrated?
Shiva devotees observe strict fast on Maha Shivaratri, with many people having only fruits and milk and some not even consuming a drop of water. Worshippers dutifully follow all the traditions and customs related to Shivaratri festival, as they strongly believe that sincere worship of Lord Shiva, on the auspicious day, releases a person of his sins and also liberates him from the cycle of birth and death. As Shiva is regarded as the ideal husband, unmarried women pray for a husband like Him, on Shivaratri. On the other hand, married women pray for the well being of their husbands, on this auspicious day.
On Maha Shivratri, devotees wake up early in the morning and take a bath, if possible in river Ganga. After wearing fresh clothes, they visit the nearest Shiva temple, to give ritual bath to the Shiva Lingum (with milk, honey, water etc). The worship continues the whole day and whole night. Jaagran (nightlong vigil) might also be observed in Lord Shiva temples, where a large number of devotees sing hymns and devotional songs, in praise of Lord Shiva. In the morning,g devotees break their fast by partaking the prasad offered to Lord Shiva, after the aarti, the night before.