I finally understood the symbolic significance of this first Hindu festival of the (modern) New Year, courtesy this site (excerpts):
Introduction of Makar Sankranti:
Makar Sankranti is one of the most auspicious day for the Hindus, and is celebrated in almost all parts of the country in myriad cultural forms, with great devotion, fervor & gaiety. Lakhs of people take a dip in places like Ganga Sagar & Prayag and pray to Lord Sun.
It is celebrated with pomp in southern parts of the country as Pongal, and in Punjab is celebrated …