Why is Makar Sankranti Celebrated on 14 January:
In the Hindu religion, every month is divided into two parts, The first is Krishna Paksha “Dark half of the month” and the second is Shukla Paksha “Brighter half of the month”. Similarly, each year is divided into two parts, first Uttarayan and second Dakshinayan. These two are considered together as a year. On the day of Makar Sankranti, due to the rotation of the earth, there is a slight change in the direction of the sun. Hence this period is called Uttarayan.
Sometimes it is celebrated a day earlier or later i.e. on January 13 or 15. But this is rarely seen. Makar Sankranti is related to the geography of the earth and the position of the sun. Whenever the Sun crosses the Tropic of Capricorn. That day is only on January 14, and that is why this day is celebrated as the festival of Makar Sankranti.