Mahamaham is a Hindu festival celebrated every 12 years in the Mahamaham pond located in the South Indian town of Kumbakonam in Tamil Nadu, India. Hindus consider taking a holy dip at the Mahamaham tank on the day of Mahamaham as sacred. The last Mahamaham was celebrated on February 22, 2016 with over a million people from various places taking the holy dip in the Mahamaham tank.
In the northern bank mandapa, there is an inscription of Tulapurshadana, a practise of weighing oneself against gold. The ceremony is observed during various times like equinoxes, commencement of an era (Yuga) and its ending, eclipses and Makara Sankranti. The ceremony is usually performed in sacred places like temples, rivers and tanks. The amount of gold thus weighed is distributed among deserving men. As per legend, after the end of each era, the whole world immerses in a deluge on account of the wrath of Hindu god Shiva for the sins committed by humans in earth. Brahma, the Hindu god of creation, recreated the world during the start of current Kali Yuga . Shiva declared that after the end of previous era, a divine pot would reach a holy spot. As the divind pot reached Kumbakonam, Shiva, in the form of a hunter, broke the pot with an arrow. The pot broke into many parts and scattered around, which became the cause for so many temples in the town - Kumbeswara, Someswara, Kasi Viswanatha, Nageswara, Kamata Viswanatha, Abimukeshwara, Goutameswara, Banapuriswara, Varahar, Lakshminaryana, Sarangapani, Chakrapani and Varadharaja. Brahma prayed to Shiva to allow pilgrims to visit the tank during the sacred occasion. Lord Shiva accepted the demand and is believed to arrive along with Vishnu and other celestial deities at the centre of the tank.
Astronomically, maham or magha is a nakshatra (constellation) in Leo sign (Simha Rasi). Since Sun takes a year to go round (as viewed from earth, as if earth is stationary), this festival is celebrated in the month when full moon occurs as moon is passing Magha nakshatra (Leo sign) and Sun is on the other end in the opposite Aquarius sign (Kumnha Rasi). Jupiter or Guru takes twelve years to go around to complete one full revolution and during this sojourn, it spends one year in Leo once every twelve years. Mahamagham occurs once in twelve years when the planet Jupiter's residence in Leo coincides with full-moon in Leo. This is also considered a powerful astrological combination since Jupiter and Moon will be on the same constellation with Sun on the other side, which is considered very auspicious and highly beneficial. On the day of the festival, it is believed to bring all water bodies together and enrich the tank with minerals. Similarly, a lake in Kotihar in Jammu and Kashmir gets full supply of water the same day, which otherwise remains empty during the other 11 years. Since Brahma reconstructed the world after the last deluge, there is a temple dedicated to him in Kumbakonam, though he is cursed not to have any temple for him anywhere else.