Today is a auspicious day of Shivratri. But why do we celebrate Shivratri? There are numerous Mahashivaratri stories related to  this event:

The first is that on this day, Lord Shiva wed Parvati. It is therefore a celebration of this divine union.

Another is that a pot of poison      appeared when the Gods and demons stirred the ocean together to obtain the      ambrosia that was hidden in its depths.

By consuming this poison, Lord Shiva protected both the Gods and humanity. The Lord's throat became infected by the poison, turning him blue. Shivratri is observed in remembrance of world's rescuer.

Another mythology holds that Lord Shiva held Lady Ganga in his matted hair as she descended from heaven in full force and then released her as numerous streams upon the Earth.

 This saved the planet from catastrophe. On this lucky night, the Shivalinga is bathed as a devotion to Him.

 Moreover, it is said that at midnight, the shapeless Deity Sadashiv manifested as a Lingodhbhav Moorthi. As a result, many pray to God throughout the night.