It must be noted that Kalashtami is observed on the eighth day after the full moon in all months by Shiva devotees.
Legend has it that it Lord Shiva in the form of Mahakaleshwar chopped off the fifth head of Brahma and performed penance on this day. There are several legends regarding the reason for chopping off the fifth head of Brahma. One legend has it that the Trimurti – Brahma, Vishnu, and Shiva once had an argument over who is the most powerful. During the argument, Brahma uttered a remark which enraged Shiva. Suddenly, he produced Bhairava from his body and ordered to chop the head of Brahma.
This terrified the demigods (Devas) and humans. This form of Shiva is believed to punish sinners and he carries a ‘Danda’ – a rod to punish.
The most popular Bhairava Ashtami is observed on the eighth day during the waning phase of moon in Margashirsha month in traditional Hindi calendar.
Kal Bhairav vehicle is a black dog and in some regions as part of ritual dogs are fed on the day.
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