It's Makar Sankranti today, probably the only Indian festival which is based on the position of Sun. Rest all are as per lunar calendar.
Sometimes I wonder why is it so? Is Moon more important than Sun? It can never be. .
One of the reasons may be that since our ancestors did not have access to calendars thousands of years ago, they used to keep track of the days using the different phases of moon which is quite easy thing to do. May be for the same reason there are very few festivals during the monsoon as the moon was not visible in cloudy nights.
Sun based calendar were a later invention.