Today is a harvest festival. In the South, particularly Tamil Nadu it is celebrated as Pongal. In other parts of India it is Sankranthi.
It is a day to celebrate the beginning of the harvest season.
It's interesting to me that it falls in January. I think it shows how festivals and holidays form differently in different parts of the world because of differences in weather. Weather has such a tremendous effect on the development of society and culture, since we all started out as hunter/gatherer and moved into agriculture (from what I understand of anthropology, anyway).
In America, harvest festivals all occur in October and November. There is Thanksgiving and there is Sukkot, a Jewish holiday. Harvest festivals here are connected to trees that turn yellow, orange, and red; to corn and pumpkins and other gourds.
Pongal in Tamil means "spilling over." Using a clay pot to boil milk until it runs over symbolizes prosperity and abundance. The festival is dedicated to the sun God, Surya.
Sankranthi is celebrated differently in different areas, so I will simply link to the Wikipedia article about it.