Shuddha saptami of Magha month is the birday of Surya (Sun). It is celebrated as Surya Jayanti and Ratha Saptami in India. Rangoli in the shape of Rath (Chariot of Surya) is made before the houses and in the middle of it bonfire made of cow dung cakes is made and payasam is prepared on it.
Sun temple in Konark Orissa and Arasavalli in Andhra Pradesh are popular celebration places of this festival.
About Sun in Hindu Encyclopedia