Genealogy
Samjna replacing herself by Chaya as wife of Surya
Kashyapa and Aditi had a son named Vivasvana. He was very bright and was thus known as the Sun god or Surya.
Surya was married to Samjna, Vishvakarma’s daughter. They had two sons. The first son was Vaivasvata Manu and the second son was Yamadharma, the god of death. Yama had a twin sister named Yamuna.
Surya loved his wife and children very passionately. Samjna also loved her husband very much, but since Surya’s energy was intolerable Samjna could not stay with him for long or look at him. So she created an exact replica of her, gave it life and named it Chhaya (shadow).
Samjna told Chaya, “I cannot bear the energy of my husband, so I am going off to my father’s house. Stay here, pretend to be myself before my husband and take care of my children. Under no circumstances tell anyone, certainly not to my husband, that you are not Samjna.”
Chaya accepted what was told to her by her creator, but with a small exception that she may reveal the truth if something unbearable like cursing her or pulling her hair by force in an angry mood or something like that happens.
When Samjna went to her father’s house, her father Vishvakarma asked her to return to Surya. But she told him about her inability to stay with her husband and the arrangement she made there. Then, she went to a place known as Uttara Kuru, disguised herself and live there as a mare.
Meanwhile, Surya, who had not realized that Samjna had been replaced by Chhaya, had two sons in Chaya. They were named Savarni Manu and Shani (Saturn). As soon as Chahaya had her own children she no longer cared Samjna’s children. Vaivasvata Manu, the elder son was very quiet and never responded for the neglect he received. But Yama was not that tolerant. One day he raised his leg to kick Chaya. At this, Chaya cursed Yama that his legs would fall off.
Yama went and complained to Surya. “I have not really kicked her, he said. I only threatened to do so. And does a mother can ever curse her children like this?”
“I can’t fully undo the curse”, replied Surya. “At best, I can reduce its severity. Your legs will not actually fall off. Some of the flesh from your legs will fall off onto the earth and create worms. Thereby, you will be freed of your curse.”
Surya felt that there was some truth in Yama’s asking whether a mother would ever curse her children. He questioned his wife. But Chaya revealed nothing and kept silent. Surya then grasped her by the hair and threatened to curse her. Since her both conditions were now violated, Chaya revealed the truth.
In an extremely angry mood, Surya went to Vishvakarma’s house. Vishvakarma then advised Surya, “It is all because of your excess energy that all this has happened. If you permit, I will shave off some of the extra energy. Then Samjna will be able to look at you.”
Surya agreed to this proposition and Viswakarma shaved off the excess energy of Sun. With the shaved off energy, Vishvakarma manufactured Vishnu’s chakra (bladed discus).
Then Surya went in search of his wife Samjna and found her in Uttara Kuru in the form of mare. He joined her there in the form of a horse. As horses (Asvins), they had two sons named Nasatya and Dasra. Nasatya and Dasra were also called as Asvin Kumars, as born to Asvins(Horses). Both of them later became the royal physicians of the gods.