Saptami Tithi is dedicated to Lord Surya. Shukla Paksha Saptami in Magha month is known as Ratha Saptami or Magha Saptami. It is believed that Lord Surya started enlightening the whole world on Ratha Saptami day which was considered as birth day of God Surya. Hence this day is also known as Surya Jayanti.