A Year on Earth: How to Measure a Complete Trip Around the Sun

This video shows how we actually measure a year on Earth. Since our planet’s orbit around the sun does not follow a perfect circle, it does not return to its starting point in space after one year.

There are different methods for measuring a year.

A sidereal year is measured by observing the position of the sun relative to the stars. When the sun takes a course through the constellations on a path called the ecliptic, and returns to its starting point, one sidereal year has passed.

Another method is the tropical year where the year is measured according to the position of the sun relative to the tilt of the Earth’s axis.

If the sun were to be observed every day at noon, we would realize its position is constantly changing, following a trajectory called an analemma. From these calculations we can determine the equinoxes and solstices throughout the year.

The video ends with a detailed description of the gradual and cyclical changes that influence the length of a year on Earth, such as axial precession and axial tilt.