Sidereal years are astronomical markers used to measure the time it takes for the Earth to complete one orbit around the Sun relative to the fixed stars. These years are also known as stellar years and are a crucial parameter in calculating the positions of stars and other celestial bodies. Another synonym for sidereal years is tropical years, which is the time it takes for the Earth to complete one orbit around the Sun relative to the vernal equinox. The vernal equinox is the point where the Earth's orbit intersects the celestial equator, and this point moves slightly each year due to precession. Thus, using tropical years provides a measure of the Sun's position at the same equinox each year.