Rahu is the Head of Demon Snake that swallows the sun or the moon causing eclipses according to Hindu scriptures.
He is depicted in art as a dragon with no body riding a chariot drawn by eight black horses.
He is an Tamas Asura who does his best to plunge any area of one's life he controls into chaos.
The rahu kala is considered inauspicious.
According to legend, during the Samudra manthan, the asura Rahu drank some of the divine nectar.
But before the nectar could pass his throat, Mohini (the female avatar of Vishnu) cut off his head.
The head, however, remained immortal and is called Rahu , while the rest of the body became Ketu.
It is believed that this immortal head occasionally swallows the sun or the moon, causing eclipses.
Then, the sun or moon passes through the opening at the neck, ending the eclipse.
The king of the nagas, Rahu prayed to Lord Siva and hence this place got the name Thirunageswaram.
Here Rahu Bhagavan has manifested with both his consorts.
At this sthala, the colour of milk changes from white to blue during Abhishekam.
On 16.2.86, a snake had shed off its outer skin on Rahu Bhagavan, which is preserved and worshipped to date.
The abode of Uppiliappan, which is also hailed as 'South Tirupathi', is situated very close to this temple.
Of the 127 temples located to the South of river Cauvery, this temple is amongst the most prominent.
Suryan, Vinayagar, Gautamar, Nalan, Parasarar, Pandavas, Vasishtar, Indran, Brahma, Bageerathan, Chandrasenan, Adiseshan, Kakkan Karkodagan, Sounagar, Nargunan have prayed and benefited at this sthala.
King Sambumali who had incurred the wrath of sage Kaalangiri, attained moksha after bathing in the temple tank and praying to the Lord and Ambal of this temple.
Rahu is the source of plenty. Kalathra dosham, puthira dosham, communicable diseases, mental disorders, leprosy, fall in grace are caused by Rahu dosham.
Praying to Rahu at this sthala helps rid a person from these factors and also saves the person from all poisonous life forms.
Trips to holy places, Gnanmarkam are his beneficial aspects.
The sthalam of Rahu is Thirunageswaram, which is located 6 kms from Kumbakonam, enroute to Karaikal.
The presiding deities are Naaganaadar and Girigujaambigai.
He faces the South-West direction. The Adi Devatha is Durga and the Prathyathi Devatha is the snake.
His colour is black,
his vahana is blue lion;
the grain associated with him is orid;
the flower-mandarai;
fabric-black cloth;
gem- Komedagam;
food-rice mixed with orid dhal powder.
The Skanda Purana says that Rahu is instrumental in strengthening ones power and converting even an enemy into a friend
The effect of snake bite is removed by his grace.
The lunar and solar eclipses are attributed to Rahu and Ketu Rahu and Ketu stay 1 1/2 years in each Griha.