Margasirsham-the ninth month of the Hindu lunar calendar ( November 26-December 24)

Margasirsha maasam the ninth month of the Hindu lunar calendar is believed to be one of the auspicious months devoted to Lord Maha Vishnu. Some of the major festivals celebrated in this month are Subrahmanya Sashti (November 30), Geetha Jayanthi (December 6), Dattatreya Jayanthi (December 10), Dhanurmaasam a solar month starts on December 17. 

Subrahmanya Sashti (November 30) - It is on this day that Sri Subrahmanya was born on sixth day after amavasya in Margasirsha maasam. He is the son of Lord Shiva. A year later on this same day he killed the invincible demon Tarkasura and released the Devas from Taraka’s oppression. Lord Subrahmanya is the lord of War. He is known with different names. He is called as Kumara, as he always looks like a small boy. He is called Shanmukha as he has six faces. He is called Kartikeya as he was brought up by six mothers named Kruttikas. Lord Subramanya Swamy is considered to be the universal lord who blesses human beings and helps them get rid of their sins. Subrahmanya has two spouses, Valli and Devasena. They represent will (Valli) and action (Devasena). He also holds a spear given by his mother Sakti for removing the evil force of Taraka. This spear (Vel) represents (Jnana) knowledge. These three together denote the three cosmic energies of governing will, action and knowledge. He rides on peacock, indicative of conquering pride egoism and vanity. Shashti celebrations include by performing puja to the Lord offering milk, chimmiri (prepared with sesame seeds and jaggery), and some temples perform kalyanam (marriage) of Subrahmanya Swamy with Valli and Devasena. Lord Subrahmanya is worshipped in India (mostly South India), Sri Lanka, Malaysia and Singapore.
May Lord Subramanya Swamy shower His blessings on you!

Geetha Jayanthi (December 6)-The Geetha Jayanthi Day or the Birthday of Srimad Bhagavad Geetha is celebrated traditionally on the Ekadasi 11th day after the amavasya of Margasirsha. This was the day on which the discourse was given to Prince Arjuna of the Pandava dynasty by Lord Krishna on the battlefield of Kurukshetra in the greatest epic, Mahabharata. In the Geetha, Lord Krishna says, "Of all the months I am Margashirsha." hence the importance of this month.  The below slokam tells about the significance and spiritual importance of margasheersha maasam. 
Bruhatsama thatha samnam
Gayatri Chandasamaham
Masanam Margashoham
Ruthunam Kusumakarna 

It means – Lord Krishna says “I, myself, stay in Bruhathsama in the Samaveda, Gayatri in Chandassu or literature, Margasirsha or Margashira in months and Vasant rithu in rithus or seasons”. 
Geetha is one of the most often quoted Hindu scriptures within Indian (and perhaps even Western) literature. The 700 slokas or teachings of the Geetha are broad, sublime and universal. They do not belong to any particular cult, sect, creed, age, place or country. They are meant for all. The Geetha has a message for the solace, peace, freedom, salvation and perfection of all human beings.”

Dattatreya Jayanthi (December 10)-Dattatreya Jayanthi is birthday of Lord Shri Dattatreya, one of the most important Guru of Vedanta. Dattatreya is said to be an Avatar, an incarnation of Brahma, Vishnu and Shiva. The word Datta means “Given”, Datta is called so because the divine trinity has “given” themselves in the form of a son to the sage couple Atri and Anasuya. Dattatreya is pictured with the cow and the dogs, symbol of the most and least sacred creatures- everybody can attain enlightenment. Cow, here represent mother earth, dogs, represent the four Vedas who are under the protection of the Lord. Lord Dattatreya is worshiped in many places in India. The day is marked by special pujas and rituals. One of the famous temple of Dattareya Swamy, I happened to visit is in Gangapur, Karnataka state.

Dhanurmaasam a solar month starts on December 17- Dhanurmaasa 2011 begins on December 16 and ends on January 14, 2012. 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. Dhanurmasa is considered as Shooonya Masam. The period is considered inauspicious in some regions. It is considered as inauspicious to do any good things other than Godly functions. Worship of Lord Vishnu during the morning hours in Dhanurmasa is considered highly auspicious. The songs of Thiruppavai will be cleansing the air all around devotees reciting Thiruppavai will be shivering in the cold as they go around the main roads of the village. This prakriya is Nagara sankeerthanam (mass spiritual awakening). There is a belief that worshiping Lord Vishnu on a single day during Dhanurmasam is equal to worshiping him for thousands of years. 

With the advent of the Dhanurmaasam , the thresholds of every house in Andhra — towns and villages alike — bloom with white and colored geometrical patterns called muggu (rangoli). It is such a common sight that we often tend to forget the significance of the muggu and that too in this particular month. First, this month is said to be devoted to spiritual thinking. Since cleanliness is next to godliness, we believe that God enters only those households that are clean from all angles. It has therefore become a custom to water the front yard of one's house and then lay a decorative muggu as if inviting God to take the first step into their house.

This month culminates with the Makara Sankranti festival and the Uttarayana (winter solstice) punyakaalam.