Katyayani Vratam, a Puja dedicated to Goddess Kathyayani, is observed during Dhanurmasam or Dhanu month in South India. In 2015-2016, Katyayani Vrata starts on 17 December 2015 and ends on 14 January 2016. In some places, the Vrata is observed in Margashirsh month and in some places during Dhanurmasam.
The Lunar month of Margashirsha month is considered as Dhanumasam or Margali masam in Solar calendar. Mentioned in the Bhagavata Purana, Devi Mahatmyam, Taittiriya Aranyaka, part of the Krishna Yajurveda, and Skanda Purana, Katyayani Vrat is of great significance and spiritual importance.
The Bhagavata Purana mentioned the legend or story or vrat katha of Katyayani Vrata during which young marriageable girls (gopis or gopikas) of Gokula in Braja, took Goddess Katyayani vrata to get Lord Sri Krishna as their husband.
It is observed in the month of Margashirsha which coincides with the Solar month of Dhanurmasam. In Tamil Nadu, Katyayani Vrata is known as Pavai Nombu or Margali Nombu which starts on Dhanur Sankranthi day and ends on the first day of the Tamil month of Thai masam.