Sidereal Year

A sidereal year is the time it takes for the Earth to complete one orbit around the Sun, measured with respect to the fixed stars. Unlike the tropical year, which is based on the seasons, the sidereal year is based on the position of the stars.

Key Points to Remember

• The sidereal year is approximately 365.25636 days long.
• It is about 20 minutes longer than the tropical year due to the precession of the Earth's axis.
• Since the Earth's axis precesses, the position of the stars at the vernal equinox shifts slightly each year, causing the sidereal year to be slightly longer than the tropical year.

Study Tips

When studying the sidereal year, it's important to understand the difference between the sidereal and tropical years, as well as how precession affects the length of the sidereal year.

Key Terms

Make sure to familiarize yourself with the following key terms:

• Sidereal Year: The time it takes for the Earth to complete one orbit around the Sun, measured with respect to the fixed stars.
• Tropical Year: The time it takes for the Sun to return to the same position in the cycle of seasons, approximately 365.24219 days long.
• Precession: The slow change in the orientation of the Earth's axis, causing the position of the stars at the vernal equinox to shift over time.

Practice Questions

1. What is the difference between a sidereal year and a tropical year?
2. How does precession affect the length of the sidereal year?
3. Why is the sidereal year approximately 20 minutes longer than the tropical year?