As per Hindu lunar calendar the month in which full moon day coincides with Makhah (Maghah) star, that month is denoted as Maagha masam which occur during the calendar months of January-February.  Makhah also means Yagna and Lord Vishnu is referred to as MahaMakhah (Sri Vishnu Sahasranama sthothram sloka # 47) the presiding Deity of Yagna. The Lord is also worshipped through the medium of Yagna.  Maagham is a Sanskrit word Ma+Agham. Ma means not present and Agham means sin, evil, malefic, annoyance, suffering, grief and Maagha masam is the month which is highly meritorious, auspicious and free from any sin or suffering. 
Lord Maha Vishnu in the name of Maadhava is the presiding deity (Masa Niyamaka) who governs the month Maagha Masam and to be worshipped.  We find a reference to the words Madhava in sloka #8, 18 and 78 of Sri Vishnu Sahasra Nama Sthothram.  Madhava means one who is the consort of Goddess Lakshmi Devi, one who is the bestower and Lord of superior knowledge.  Astrologically, Kethu the Mokshakaraka is regarded as the ruling planet of Magha star and Pithru Devathas as the presiding Deities. Maagha masam, the eleventh month as per Hindu lunar calendar is considered as an auspicious month for performing marriages, upanayanam, Gruha Pravesam, Aksharabhyasam etc.
Significant days of Maagha masam:
During Maagha masam we find several significant and sacred days to be celebrated.  To begin with,
Maagha sukla Panchami the fifth day of Maagha masam in the bright fortnight is celebrated as Vasantha Panchami also known as Sri Panchami. Goddess Saraswathi, the presiding deity of Akshara Gyana, the female Divine energy of Learning, Knowledge and Wisdom is said to have born on this auspicious day of Sri Panchami. Dedicated to Vaakk Devi (Goddess Saraswathi) this day is considered to be highly auspicious day especially for Aksharabhyasa (inducting a child into education).  Goddess Saraswathi is to be worshipped on this day to get rid of our sluggishness, lethargy and ignorance.
Ratha sapthami also known as Magha Sapthami or Maha Sapthami is a very popular Hindu festival dedicated to Sun God, Sri Surya Narayana.  It occurs on the seventh day (Sapthami) of Magha Masam during sukla paksha.  It is celebrated as Surya Jayanthi the day on which Sun God was born to Sage Kashyapa & Aditi and considered as an incarnation of Lord Sri ManNarayana. Special celebrations are held at all Vaishnavite temples especially at Tirumala and Srirangam apart from Arasavelli and Konark.  It is an age old custom and tradition that people on this day take special bath with seven Arka leaves.
Bheeshmaastami is associated with Bheeshma Pitamaha, the most revered and grandiose character of the great Epic, Mahabharata.  It was on this day Bheeshma had his last breath and this day is commemorated as the day of his Niryana.  Bheeshmaastami occurs on the 8th day (Ashtami) of the bright fortnight (Sukla Paksha) in Magha Masam, the day after Ratha Sapthami.
Sri Madhwa Navami falling on the 9th day of Lunar month of Magha Masam during the bright fortnight is associated with Sri Madhwacharya one of the greatest Hindu Saints and Philosophers who was the founder and exponent of Dvaita Philosophy.  It is said that it was on this day in the year 1317 AD, Sri Madhvacharya while teaching his disciples at Udupi Sri Anantheshwara Temple, suddenly a heap of flowers were showered on him and he disappeared from that heap of flowers not to be seen later.  It is considered as the day He entered the Badarikasrama.
Maagha Pournami the full moon day in Maagha masam is celebrated as Maha Maaghi.  This day marks the end of Maagha Snana vratham.  It is said and believed that any Divine worship, prayer, charity or rites performed on this day are highly meritorious that gives significant results. Thilapaathra Danam is prescribed to be given to a Brahmin on this day of Mahamaaghi.  Taking bath in a sea on this day is considered as highly meritorious.
Maha Shivarathri a festival dedicated to Lord Shiva occurs on the 13th /14th day of dark fortnight (Krishna Paksha) in Magha Masam coinciding with Chaturdasi thithi.  Worshipping Lord Shiva on this day of Maha Shivarathri is considered as highly meritorious and sin remover. Special celebrations are held on the eve of Maha Shivarathri at all the holy Shiva Kshetras where lakhs of people gather to offer their obeisance and salutations to Lord Shiva the great destroyer of sins and the most benevolent God.
Sunday associated with Amaavaasya + Sravana Nakshatra + Vyatheepatha Yoga + in the lunar month of Pushya or Maagha is referred to as Ardhodhaya which is considered to be a very sacred day, a parvakala that occurs very rarely that is more meritorious than an eclipse. Maagha Bahula Amaavasya associated with Satabhisha star is considered as highly sacred and meritorious. According to Dharmasindhu by performing Pithru  Shraaddha on this day, Pithrus (ancestors) gets pleased for ten thousand years.
Charities during Maagha masam
During Maagha masam following charities are prescribed to be given which is considered as highly sacred and meritorious.
Veni Danam at Prayaga, Thila-Paathra Danam (Black/white sesame seeds along with a copper or a bronze vessel), Salagrama Dana, Anna Dana (Food), Gold or gold items, Hiranya danam, Thila (Sesame) + Sugar in the ratio of 3:1, Kooshmaanda Danam (Pumpkin).  Apart from the above Thila homa and Thila bhakshana are also prescribed during Maagha masam.
Maagha Snanam
While Kartheeka masam is given lot of significance for lighting of lamps, Maagha masam is given special significance for taking bath that is known as Maagha Snanam.  It generally starts from Pushya sukla Pournami and ends with Magha sukla Pournami or it can also be from Makara Sankramana to Kumbha Sankramana as per Solar/Luni-Solar calendar. For followers of lunar calendar it starts from Pushya Bahula Amaavaasya and ends with Maagha Bahula Amaavaasya.  During this period it is prescribed to take bath early in the morning before Sunrise preferably during Arunodaya kala. This sacred bath is preferred to be taken in any river, lake or theertha or at least at home. Apart from the daily routine (Nithya Karma) special arghya is to be given to Lord Madhava and Sun God after Maagha Snanam.
Merits of Maagha Snanam:
Taking a bath (Snana) which is refreshing, not only cleanses our external body, but also has been given lot of significance from the religious and spiritual point of view in the daily routine of an individual. In Hindu philosophy daily routine generally begins with a bath before worshiping God, a discipline that is inculcated with a sense of cleanliness in our actions. When it is during an auspicious period like Maagha masam, its spiritual merits are in multiple.  It is said that Maagha Snana can purify a person even from ghastly and dreadful sins committed.  Taking bath in Maagha masam, early in the morning as said above is highly sacred, spiritual and meritorious.  Sacred texts like Vayu Purana, Brahmanda Purana are said to have made a reference to the merits and significance of Maagha Snanam. Its merits get increased depending on the place where the bath is taken as given below. 
  • At home with hot water – Merits equivalent to Six years of such Snana phala
  • From the waters of a well –12 years of such Snana phala
  • In a lake –24 years of such Snana phala
  • In any river – 96 years of such Snana phala
  • In any sacred river – 9600 years of such Snana phala
  • At the confluence (Sangam) of sacred rivers–38400 years of such Snana
  • In Ganges River – Merits equivalent to 38400000 years of such Snana phala
  • At Triveni Sangam (Prayaga) – 100 times of Ganga Snana phala
  • Maagha Snana in a sea (Samudra) is considered as more meritorious than all the above.
  • Wherever bath is taken, one should always remember to recollect Prayaga and also pray Maasa Niyamaka Sri Maadhava (Lord Vishnu) silently. Those who cannot take bath as said above for the entire month should at least take it for the last three days which is known as Anthya Pushkarini.  Maagha Snanam is prescribed for all ages of men and women.

 Courtesy:Bharagava Sharama