Base article source: drikpanchang.com
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 Dev 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.
Ratha Saptami is highly auspicious day and it is considered as auspicious as Surya Grahan for Dan-Punya activities. By worshipping Lord Surya and observing fast on this day one can get rid of all type of sins. It is believed that seven types of sins done, knowingly, unknowingly, by words, by body, by mind, in current birth and in previous births are purged by worshipping Lord Surya on this day.
On Ratha Saptami one should take bath during Arunodaya. Ratha Saptami Snan is one of the important rituals and is suggested during Arunodaya only. Arunodaya period prevails for four Ghatis (approx. one and half hour for Indian locations if we consider one Ghati duration as 24 minutes) before sunrise. Taking bath before sunrise during Arunodaya keeps one healthy and free from all types of ailments and diseases. Because of this belief Ratha Saptami is also known as Arogya Saptami. Taking bath in water body like river, canal is preferred over taking bath at home. DrikPanchang.com lists Arunodaya period and sunrise time for most cities across the globe.
After taking bath one should worship Lord Surya during sunrise by offering Arghyadan (अर्घ्यदान) to Him. Arghyadan is performed by slowly offering water to Lord Surya from small Kalash with folded hand in Namaskar Mudra while facing Lord Sun in standing position. After this one should light Deepak of pure Ghee and worship Sun God with Kapoor, Dhup, and red flowers. By doing morning Snan, Dan-Punya and Arghyadan to Suryadev one is bestowed with long life, good health and prosperity.
This day is also known as Achala Saptami.
Please have erukku leaves, Akshadhai and keep it in head during bath.
Slokam during bath
Saptha Sapthi priye Devi
Saptha Loka Su Poojithe
Saptha JanmaaRchitham Paapam
Hara Sapthami Satcharam
Naumi Sapthami Devi Thwaam
Saptha Lokaika maatharam
SapthaaRka patra Snaanena
Mama Paapam Vyapohaya ||