Dhanurmasa

Dhanur Mas, or Dhanurmasa, is an important period in traditional Hindu calendar. The month is known as Dhanur Maas as the sun transits through the Dhanur Rashi (Sagitarius) and the period ends with the Makar Sankranti. In some regions the first day of Dhanur Maas is known as Dhanur Sankranti. In North India in 2008, Dhanur Masa begins on December 15 and ends on January 13, 2009. The period is highly auspicious, Daan (donations), Japa, tapa (dhyan) done in this month is believed to yeild lot of good.
It must be noted here that in South India ,this month is known as Dhanurmasam, begins on December 16 and ends on January 13, 2009.
Dhanur Mas is not an independent month in any Hindu calendar. It begins in the middle of Margashirsh month in Gujarati and Marathi calendar. In North Indian, calendar it begins in the beginning of Poush month. Dhanur Mas is therefore the period the sun shifts from the Dhanur rashi to Makar Sankranti.
The Ekadasi falling during this period is considered highly auspicious. In South India, especially the Vaikunta Ekadasi which falls during the waning phase of the moon in Dhanur Mas attracts thousands of devotees.
- courtesy- Hindu blog