Dhanur Sankranti, also known as Dhanu Sankramanam, is the transition of the Sun to Dhanu Rashi or the zodiac sign of Sagittarius. In 2009, Dhanu Sankranti date is December 16. Usually, Dhanu Sankraman occurs on Margasira Amavasya as per Telugu and Kannada calendars. As per Tamil calendar, Dhanus sankraman falls on the first day of Margazhi or Margali masam (Margazhi Amavasi).
Dhanur Sankraman marks the beginning of Dhanur Masam in Andhra Pradesh and some parts of Karnataka. Dhanurmasam is the most auspicious period for Vaishnava sect of Hindus. Pavai Nombu begins on Dhanur Sankraman day in Tamil Nadu and Kerala.
Pavai Nombu, also referred as Margazhi Nombu, is a month-long vrata observed during the Tamil month of Margazhi or Margali masam. In 2009, Pavai Nombu starts on December 15 and ends on January 14, 2010. 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. Thiruppavai is the sacred text recited during Dhanurmasa vratham. Dhanurmasam is one of the most auspicious months for Vaishnava sect of Hindus. It starts on Margashira Amavasya, the No Moon day in Margasira masam.