Wiki says it is the day the sun travels towards the north on the celestial sphere. But I thought, we were taught in class eight that the sun is over the Tropic of Capricorn on Dec 22nd (Winter Solstice). So by definition, the Sun travels north on every day after that. Why is it that we celebrate the “Uttar”ayan on Jan 14th? And, if the logic is that the sun enters the northern hemisphere on Jan 14th, it can’t be true as the sun only reaches the equator on the equinox, i.e., March 21st. Also, it cannot be said that the Sun travels northwards over India (it is majorly an Indian festival) as India lies completely in the Northern hemisphere and thus when the sun has not even crossed the equator, it cannot be over India. Then, sun travels to the north of what is the question that remains unanswered.
Ironically, while most Indian festivals are based on the lunar calendar, this is based on the solar calendar (few others include Vishwakarma Jayanti). I conclude that this festival is just another harvest festival and an attempt was made to give it a scientific meaning by the pundits (no disrespect meant). Of course, contradicting views with references are invited.