A sidereal year is the time it takes for the Earth to complete one full orbit around the Sun relative to the fixed stars. This period is approximately 365.256 days long. It differs from the more commonly known tropical year, which is about 365.242 days and is based on the cycle of the seasons. The difference between these two types of years arises because of the precession of the equinoxes, a slow wobble in the Earth's rotation axis. This precession causes the position of the equinoxes to shift over time, affecting the timing of the seasons compared to the stars.