A
tropical year (also known as a
solar year), for general purposes, is the
time that the
Sun takes to return to the same position in the cycle of
seasons, as seen from
Earth; for example, the time from
vernal equinox to vernal equinox, or from
summer solstice to summer solstice. Because of the
precession of the equinoxes, the
seasonal cycle does not remain exactly synchronized with the position of the Earth in its orbit around the Sun. As a consequence, the tropical year is about 20 minutes
shorter than the time it takes Earth to complete one full orbit around the Sun as measured with respect to the fixed stars (the
sidereal year).