The Transit of Sun into the constellation of Dhanurrasi or Sagittarius and until it moves out to the constellation of Makara or Capricorn. Since the transit into Dhanur rasi, it is known as Dhanurmasam.
Dhanurmasa / Marghasirsha / Margazhli (Dec 16 to Jan 13) has great spiritual significance which starts with Margashirsha shukla ekadasi (the eleventh day in the bright half of the lunar month of Margashira) and extends up to the end of dakshinayana. When the sun starts moving northward from the Topic of Capricorn to the Tropic of Cancer called uttaraayana and when the sun moves southward is called dakshinaayana. According to the Shasthras, one human year represents to one day for the celestials. Uttaraayana is their daytime and Dakshinaayana is the night. The six months of Uttarayana (mid Jan to mid July) are a single day time of the Gods and the next six months of Dakshinayana (mid July to mid Jan) are a single night of the Gods. And Dhanur / Margazhi Maasa being the dawn of the day (Brahma Muhurtha) for the Gods, singing and chanting the glory of God is considered most auspicious and said to bestow the Human desires very soon. Thus a year of twelve months is single Nychthemeron (The natural day and night, or space of twenty-four hours) of the Gods.
Dhanurmasa is also called as Dhanur Sankranthi, Shoonya Masa meaning blank because it is considered inauspicious to do or commence any good affairs related to Business or otherwise, except worship of Gods. This month is allotted to Gods and for us to completely immense in divine thoughts. Lord Krishna himself declared in the Bhagavadh Gita that “I manifest the most in the month of Margashira / Dhanurmasa among the months of a year. This highlights the religious significance of Dhanurmasa in the Hindu calendar. For this reason, sages have set apart this month to be completely focused on devotional activities. Other non-devotional social activities such as weddings, House warming ceremony, commencing a business or a shop etc, are totally prohibited during this month so that attention can be given exclusively to the worship of God without any diversions or distractions. Scriptures recommend Dhanur Masa Pooja for prosperity. longevity and above.
Apart from the religious and spiritual thought, Scientifically said that the Ozone layer will be very clean during the early mornings hours of this month due to the cold whether, and also you can breathe fresh and pure oxygen, can posses high cosmic energy very soon when meditated during the morning hours.
Cold weather (winter) is the most ‘creative’ weather for production of all kinds of species. Wake up early in the morning, having bath and going for a walk amidst fresh & cold air gives the ultimate energy, feel fresh and relaxed, thus boosts your energy to the maximum.