Many erroneously believe the change in seasons to be the result of a change in Earth’s distance from the sun, with the warmer summer season being a result of a shorter distance between us and our star. If this were true, however, it would mean that the entire planet would experience summer at the same point during the year – something which is not the case.

In fact, while the Northern hemisphere experiences the summer solstice on June 21, the Southern hemisphere’s summer solstice is exactly six months later, on December 21.

The Earth’s axial tilt also results in the changing length of day

The actual reason for the change in seasons lies in the Earth’s axial tilt. The Earth’s axis of rotation is tilted by about 23 degrees, which means that during some parts of the year, parts of the Earth are tilted farther away from the sun than others.

This tilt also results in the changing length of day observed everywhere except for the equator, where the day is always 12 hours long, irrespective of the time of year.

The Earth’s axial tilt changes between 22.1 degrees and 24.5 degrees during a 41,000-year period, with seasons being slightly more extreme as the tilt increases.