Sidereal year

A sidereal year (, US also ; from Latin'asterism, star'), also called a sidereal orbital period, is the time that Earth or another planetary body takes to orbit the Sun once with respect to the fixed stars.

Thus, a sidereal year is the interval required for Earth to travel once around the ecliptic, completing one revolution about the Sun and returning to the same orbital position relative to the background stars.

In 2025, the sidereal year equals 365.256363ephemeris days (365 days, 6 hours, 9 minutes and 9.8 seconds).

The sidereal year differs from the tropical year, "the period of time required for the ecliptic longitude of the Sun to increase 360 degrees", due to the precession of the equinoxes. The sidereal year is 20 minutes 24.7 seconds longer than the mean tropical year (365.242189 ephemeris days), or 365 days, 5 hours, 48 minutes, 45.1 seconds.