Pavai Nombu (Margazhi Nombu) is a month-long vrata observed during the Tamil month of Margazhi or Margali masam. In 2017- 2018, Pavai Nombu starts on December 16, 2017 & ends on January 13, 2018.
Mainly the Nombu is for kanyas or virgin girls who want to get good husbands and pleasant married life. It is believed that Andal was performed the Nombu to get the Lord Vishnu as her husband.
Some devotees believe that Gopis, the cowherd girls, were influenced by Pavai Nombu and started to perform Katyayani vrata.
Pavai Nombu is observed as Dhanurmasa Vratham in Andhra Pradesh and Telangana. Thiruppavai is the sacred text recited during Dhanurmasa vratham. Dhanurmasam is one of the most auspicious months for Vaishnava sect of Hindus.