Ardra, also known as Arudhara and Thiruvathira, is one among the 27 nakshatras or birth stars and numerous incidents associated with Shiva happened on this Nakshatra day.
The most important Thiruvathira Nakshatra is in the month of Margazhi (December – January) in Tamil Calendar or Dhanu Masam in Malayalam Calendar. The Arudhara Darshan takes place on the day. It is believed that Shiva performed the Nataraja dance on this day.
Another belief is that Shiva and Shakti merges on this day.
Women of certain communities observe a fast on the Thiruvathira day in Dhanu month for the peace and prosperity of the family.