Kepler's third law states that the squares of the sidereal periods of revolution of the planets are directly proportional to the cubes of their mean distances from the Sun.
That means if we based our calendar on sidereal years, the seasons would quickly get out of sync, Christmas would end up in July, dogs and cats, living together, mass hysteria!
The amount of time it takes a star or constellation to reach the same point in the sky at the same time of day is 365 days 6 hours 9 minutes 9.76 seconds, or a sidereal year.