A sidereal year is the time taken by the Earth to complete one orbit around the Sun relative to the fixed stars, approximately 365.25636 days. It is slightly longer than the tropical year, which is the basis for the calendar year, due to the precession of the equinoxes.

Sidereal Year

sidereal year

time taken by the Earth to complete one orbit

orbit around the Sun

fixed stars

approximately 365.25636 days

The tropical year, also known as the solar year, is the time it takes for the Earth to complete one orbit around the Sun relative to the vernal equinox, approximately 365.2422 days. This period is crucial for maintaining the alignment of calendars with the seasons, ensuring that events such as equinoxes and solstices occur on the same dates each year.

tropical year

basis for the calendar year

The Precession of the Equinoxes is the gradual shift in the orientation of Earth's axis of rotation, which causes the position of the equinoxes to move westward along the ecliptic relative to the fixed stars over a cycle of approximately 26,000 years. This phenomenon affects the timing of the seasons and is caused by gravitational forces exerted by the Sun and the Moon on Earth's equatorial bulge.

Relevant Degrees

Your Lessons