Makar Sankranti

Makar(a) Sankrānti (Sanskrit: मकरसङ्क्रान्ति, romanized: Makarasaṅkrānti), (transl. Capricorn Festival) also referred to as Uttarāyana, Makara, or simply Sankrānti, is a Hindu observance and a festival. Usually falling on the date of 14 January annually (15 January on a leap year), this occasion marks the transition of the sun from the zodiac of Sagittarius (dhanu) to Capricorn (makara). Since the sun has made this transition which coincides with moving from south to north, the festival is dedicated to the solar deity, Surya, and is observed to mark a new beginning. Many multi-day festivals are organised on this occasion all over India.

Source: https://en.wikipedia.org/wiki/Makar_Sankranti