Birth Of Shani

Suryadev(son of Brahma) was married to Sangya.Sangya was the daughter of Vishwakarma. Yama, the God of death and the river Yamuna and Vaiswat Manu are believed to be the childern of Sun & Sangya.Sangya finding it unbearable to live with the harsh glare of Surya's light, created her own replica and named her as chaya and asked her to behave as Surya's wife and perform all the duties and savour the privileges of a wife. She made her promise that under no condition would she reveal to Suryadev that she was not Sangya and promised to help her when needed.

Sangya went back to her father Daksha. When Daksha saw that his daughter coming back, he advised her that she better live with her husband only. The dejected Sangya did not follow her father's advise and instead transformed herself into a mare and resided in the Himalayas and started penance.

Chaya performed the role of dutiful wife. Shani was the son of Chaya & Sun. Surya did not have any doubts about Chaya. One day Sun observe that Chaya didnit treat the Yama & his siblings lovingly. This raises doubts in his mind.Chaya confessed that she was a 'shadow' of Sangya and that Sangya had gone to the Himalaya for penance. On listening he dejected chaya. This cause the enemosity between Sun & Saturn.
It is said that when he opened his eyes as a baby for the very first time, the sun went into an eclipse, which clearly denotes the impact of Shani on astrological charts (horoscope).