Dhanurmasa which falls from mid December to mid January is considered as Shooonya Masam or Kharmas. Dhanurmasa 2012 -2013 begins on December 16, 2012 and ends on January 13, 2013. The period is considered inauspicious in some regions. It is considered as inauspicious to do any good things other than Godly functions. The importance of Dhanurmasa is mentioned in the Dhanurmasa Mahatmya of Pancharatragama, Agneya Purana and also in a scripture called Smruti Muktavali.
Worship of Lord Vishnu during the morning hours in Dhanurmasa is considered highly auspicious. Vishnu Sahasranama is chanted during the period. Other important mantras chanted are those dedicated to Goddess Lakshmi.
The most popular offering made to Lord Vishnu in the month is Moong dal.
There is a belief that worshipping Lord Vishnu on a single day during Dhanurmasam is equal to worshipping him for thousands of years.
In Pancharatragama, the greatness of Dhanurmasa is presented in 4 chapters, as a conversation between Lord Vishnu in the form of a Swan or Hamsa and Lord Brahma. The dialogue between Lord Vishnu and Lord Brahma is narrated by Sage Suta in response to a query by Sage Shaunaka.
The greatness and holiness of Dhanurmasam and the rewards one gets by observing austerities in the holy month is found in the first chapter. The story of the King Satyasandha and the holiness he achieved by observing Dhanurmasa Vrata is mentioned in the second chapter. The third chapter talks about the importance of giving alms during the Dhanurmasa month. Numerous pious deeds a devotee can perform are mentioned in the chapter. The final chapter talks about feeding the poor. It is said that the best way to reach the feet of Sri Hari Vishnu is by feeding the hungry and poor.
Please note that Dhanur Masa is not an independent month in any Indian calendar except for the Malayalam calendar followed in Kerala – in this calendar the month during the period is known as Dhanu Masam. The start of the Dhanurmasam is marked by the entry of the Sun in the Dhanur Rashi (Sagittarius) called the Dhanuh Sankramana; hence the name Dhanurmasa for the period. During this month, the sun or Surya transits the Dhanur Rasi until it enters the Makara Rashi at the end of the month.