A sidereal year is the time it takes for the Earth to complete one orbit around the Sun with respect to the fixed stars. It is slightly longer than a tropical year, which is the time it takes for the Earth to complete one orbit around the Sun with respect to the spring equinox.

There are 36,525 sidereal years in a century.

There are 365,256 sidereal years in a millennium.

A sidereal year is 0.0082 days longer than a tropical year.

A sidereal year is longer than a tropical year because of a combination of factors, including the Earth's axis precession, the Earth's elliptical orbit, and the Sun's changing position over time.

A sidereal month is the time it takes for the Moon to complete one orbit around the Earth with respect to the fixed stars. It is slightly shorter than a synodic month, which is the time it takes for the Moon to complete one orbit around the Earth with respect to the Sun.

There are 12.368 sidereal months in a sidereal year.

A sidereal day is 3 minutes 56 seconds shorter than a solar day.

A sidereal day is shorter than a solar day because the Earth's axis precesses. This means that the Earth's axis slowly changes its orientation over time, causing the stars to appear to move westward in the sky.

A sidereal hour is 23 hours 56 minutes 4 seconds long.

There are 24.002 sidereal hours in a sidereal day.

A sidereal minute is 59 minutes 8 seconds long.

There are 60.001 sidereal minutes in a sidereal hour.

A sidereal second is 59.8 seconds long.

There are 60.001 sidereal seconds in a sidereal minute.