The Story of Ashwini Kumar(s) - twin sons of Surya - Part II
Sanjana, after being admonished by Surya in the presence of Shani, and being further unable to bear the glow and heat of an angered Surya, leaves his abode once again. She now cannot return to her father's house, so she disappears into a Himalayan forest to cool herself; there she takes on the disguise of a mare to prevent herself from being discovered and sent back home. She spends many long years in the forest, as a mare.
When Surya's anger cools down, he begins to miss his wife and he goes in search of her to Vishwakarma's house. Vishwakarma informs him of Sanjana's whereabouts but also has as humble request - he asks Surya to reduce his glare so that daughter Sanjana is not discomfited. Surya says he is helpless as it is part of his nature; Vishwakarma then offers to help. Vishwakarma, the celestial engineer and architect, puts his skills to use and scrapes the glow away from Surya's face and body, thus giving him, what they would say in modern day parlance - a matt-finish. Surya in his new look ventures into the Himalayan forest in search of Sanjana. He spots her grazing the grass in the form of a mare. To entice her, he takes the form of a young stallion and approaches her. Sanjana recognizes her husband and is pleasantly surprised at his efforts to woo her. She concedes, they mate, and out of this mating are born the Ashwini Kumar(s) - the twin sons of Surya. The name "Ashwini" is derived from the root "ashwa" meaning "horse".
The Ashwini Kumar(s) are given the responsibility of healing; keeping with this order, they pursue the field of medicine and emerge as the celestial physicians/doctors of Gods. The Ashwini Kumar(s) true to the horse form in which they were conceived, also hold the prime reigns amongst the 7 horses that drive Surya's chariot. Every sunrise, they come forth as the first rising rays of Sun, and are also known as "Surya-kiran".
Being the celestial physicians/healers of Gods and humanity, facing their rays during sunrise bestows good health. This is done, as per prescribed Vedic customs, by honoring their mother Sanjana or Sandhya as the Gods called her - hence we welcome the first rays of morning Sun with "Sandhya-vandanam" or "Sandhya-vandan" by offering "arghyam" or water from our palms to the rising Sun. The Sandhya-vandan is often accompanied by a chant of Gayatri mantam.
There is another analogy which I read about the Gayatri mantram - that the original Gayatri has been hidden by Gods because of its potency. But more on that - maybe next time.