Maha ShivaRathri is the festival of Lord Shiva. This festival is celebrated in the month of Magha (falling in Feb-Mar), on the Bahula Chaturdasi day (fourteenth day after the full moon), during the night. In fact, there is one such Chaturdasi day in each of the twelve months, which are referred to as Masa Shiva Rathri (meaning Shiva Rathri of the month). However, various reasons are cited in mythologies for celebrating this festival only in the month of Magha.
It is said that on the midnight of Bahula Chaturdasi in the month of Magha, Lord Shiva took the form of the great Linga (cylindrical shape whose top surface is concave). This midnight time, called the Lingodbhava time (meaning the birth time of the Linga), is the time when the Lord is worshipped.
As per the mythologies, the Shiva's Linga started growing very huge in size and occupied the entire universe at the time of its genesis and no one could fathom its beginning or end. Then, Lord Brahma and Lord Vishnu set out to find both ends of the great Linga to prove that nothing is beyond their reach. Brahma went up in the form of the divine Swan and Vishnu went downwards tunnelling in to the earth in the form of Varaha. Brahma went up and up and still could not find the top end.
On his way up, Brahma encountered Mogili flower (an aromatic flower) and a cow. So, he requested the Mogili flower and the cow to lie that he had indeed reached the Shiva Linga top and that they were the witnesses for that. Both of them obliged Lord Brahma and lied accordingly. Since he tried to belittle the greatness of Shiva, he was cursed that he is not worthy of worship by people and there won't be any temples for Brahma anywhere. Shiva also cursed Mogili flower that it will not be eligible as an offering to Lord Shiva. Shiva cursed the cow that seeing a cow's face first thing in the morning will be treated as a bad omen by the people. If at all see, its tail should be the one that can be see.
