The Puranas say that on this day Sun visits the house of his son Shani, who is the swami of Makar Rashi. These father & son do not ordinarily get along nicely, but inspite of any difference between each other Lord Sun makes it a point to meet each other on this day.
From Uttarayana starts the ‘day’ of Devatas, while dakshinayana is said to be the ‘night’ of devatas, so most of the auspicious things are done during this time.
It was on this day when Lord Vishnu ended the ever increasing terrorism of the Asuras by finishing them off and burying their heads under the Mandar Parvat.
The great savior of his ancestors, Maharaj Bhagirath, did great Tapasya to bring Gangaji River down on the earth for the redemption of 60,000 sons of Maharaj Sagar, who were burnt to ashes at the Kapil Muni Ashram, near the present day Ganga Sagar. It was on this day that Bhagirath finally did tarpan with the Ganges water for his unfortunate ancestors and thereby liberated them from the curse.