Sun worship and fast was also done in Treta and Dwapara Yuga | त्रेता और द्वापर युग में भी की गई थी सूर्य उपासना और व्रत

The worship and fast of Lord Surya is from the Vedic period itself. But according to mythological texts, Sri Ram in Tretayuga and Sambara’s son Samb in Dwapara worshiped Lord Surya. The belief behind Surya worship told in the scriptures is that by worshiping and fasting Lord Bhaskar, diseases are eradicated. Strength increases, there is defense. Also get child happiness.

Vedic period: Sun receives child on Kartik Shukla Saptami
The Sun is described as the noun and the sun is the shadow and both are called the wives of the sun. Noun was the daughter of Vishwakarma. She could not tolerate the sun’s heat. She created her own model named Chhaya and went to Kuru Pradesh to do penance herself. When Surya came to know of this, he went in search of the noun. Noun, he received on the seventh day. On this date, Surya got divine form and children were also attained. That is why Saptami Tithi is dear to Lord Bhaskar.
Validation: Sun worships, children get happiness

Tretayuga: Ikshvaku descendant Lord Rama performed Suryopasana
The son of Brahma was Marichi. Rishi Kashyap, son of Marichi. Sage Kashyap is married to Aditi. Pleased with Aditi’s penance, Surya entered Aditi’s womb with a ray named Sushumna. The part of Sun born from Aditi’s womb was called Vivaswan. His children became Vaivaswat Manu. Shani, Yama, Yamuna and Karna are the children of the Sun. Lord Rama was born in Ichvaku Kul, the son of Vaivasvata Manu. It is said that Lord Rama used to perform Chhath Vrat for the happiness of his total man.
Recognition: Sun worship protects and gets strength

Dwapara Yuga: Samb did harsh tenacity for liberation from leprosy.
Sambha, the son of Lord Krishna and Jambavati, was extremely beautiful. Due to their beauty, some distortion arose in the minds of sixteen thousand one hundred queens of God. When the Lord came to know about this from Naradji, he cursed Samb. The curse is also mentioned in the texts associated with Rudravatar Durvasa Muni, Maharishi Garg. There is a story of cursing leprosy to Samb. Samb prayed hard on the banks of the Chandrabhaga (Chenab) river. This caused his leprosy to go away. He built 12 infusion sites.
Assumption: Diseases are eliminated by offering sun to the sun.