What phenomenon causes the seasons on Earth?

The tilt of Earth's axis is the primary reason for the changing seasons on our planet. Earth's axis is tilted at an angle of approximately 23.5 degrees relative to its orbit around the Sun. This axial tilt means that during different times of the year, different parts of the Earth receive varying amounts of sunlight.

For instance, when the Northern Hemisphere is tilted toward the Sun, it experiences summer as it receives more direct sunlight, leading to longer days and warmer temperatures. Conversely, when it is tilted away from the Sun, the Northern Hemisphere experiences winter, with less direct sunlight resulting in shorter days and cooler temperatures. The Southern Hemisphere experiences opposite seasons at the same time due to this tilt.

This phenomenon is distinct from factors such as the distance from the Sun, the elliptical shape of Earth's orbit, or simply the amount of sunlight received, which do not adequately account for the seasonal variations experienced in various regions of the Earth throughout the year. While the Earth's orbit is elliptical and the distance from the Sun does change, these variations are not the driving factors for the seasons. Instead, it is the axial tilt that creates the differences in solar irradiance experienced at different latitudes during the course of the year.