uttarāyana (उत्तरायण) is the six month period between Makar Sankranti around January 14 and Karka Sankranti around July 14, when the sun travels towards north on the celestial sphere. The period from July 14 to January 14 is known is dakshināyana (दक्षिणायन). The starting of uttarayana is celebrated as Makara Sankranti throughout India, which is declared as National festival by Government of India.
Makara Sankranti (a sanskrit term) is the harvest festival of India. Sankranti means transmigration of Sun from one rāshi (zodiac in Indian astrology) to the other. Hence there are 12 such Sankrantis in all. But the transition of Sun from 'Dhanu' Rāshi (Sagittarius) to 'Makara' Rāshi (Capricorn) marks the starting of Uttarayana which means northern movement of Sun. This is particularly significant for us living in the northern hemisphere of the earth as it means the beginning of the warmer season after the rains and the cold of the winter. Since uttarayana is considered as the auspicious time, Makara Sankranti is celebrated as the beginning of that period. Diversified India has got diversified ways to celebrate this festival.
o Punjab - Lohri
o Uttarakhand - Uttarayani
o Maharashtra, West Bengal, Andra Pradesh and Kerala - Makar Sankranti
o Assam - Bhogali Bihu
o Gujarat and Rajastan - Uttarayan (Kite flying festival)
o In Tamilnadu and Tamils in Sri Lanka - Pongal
In most places, more prominently in Gujarat, Rajasthan and Maharashtra, people fly colourful kites in skies changing the skyscape entirely and bringing in a cheerful atmosphere of an important festival.
One can easily make out that this festival signifies the importance of a celestial phenomenon of the cycles within the solar system straight into our culture. It is due to this that the festival, a truly secular one, is an unique festival which falls on 14th of January each year. Naturally the celebrations too go beyond the races and religions.
I wish you all a Happy Makar Sankranti.
(with inputs from Piyush Kapopara and WWW)