Maha Sivarathri, the night devoted to Lord Siva, will be observed on Friday, the 24 February 2017. Maha Sivarathri is celebrated on Chaturdashi tithi during Krishna Paksham in the month of Magha (Masi, Feb-Jan); thus, called Maha Shivaratri.
Maha Sivarathri is believed to be the day the lord Siva and Sakthi converged and became one as Arthenareeswar. The legend is that this is the night Lord Siva performed Tandava Nrithyam, the cosmic dance. Lord Siva is the Supreme God and the destroyer and transformer of the world. It was feared that due to his destructive dance the world will end and the Thevars went and pleaded Parvathi. Parvathi worshipped Lord Siva to save the world. Lord Siva stopped dancing and took her to his left side and Siva-Parvathi became one and called Arthanareeswar.