When Lord Vishnu crushed the demon Rahu, who tried to drink the nectar during Palazhimathan or churning of the milky ocean, the head portion became Rahu; the remaining body-part acquired a snake head and became Kethu.
In Hindu astrology, Rahu and Kethu do not have any physical or celestial bodies like the other grahas. Of the two places where the Moon crosses the ecliptic (the path of the Sun), the north point is called Rahu and the corresponding South point, which is exactly 180 degrees away from the former, is called Kethu.
When the transit point of the Sun and the Moon is close to Rahu or Kethu, the Moon can intercept the light of the Sun from reaching the earth. This causes solar eclipse. When a full Moon is caused while the Moon is crossing these transit points of Rahu and Kethu, the shadow of the earth falls on the Moon and a lunar eclipse takes place.
Getting caught with bad habits, loss of property and fame, problems to children are said to be the effects of Kethudosham or affliction of Kethu.
But, if pleased he gives good health, wealth and prosperity.
The temple is dedicated to Lord Shiva and is very close to Kumbakonam.