What is the primary cause of seasons on Earth?

The primary cause of seasons on Earth is the tilt of Earth's axis. Earth is tilted at an angle of about 23.5 degrees relative to its orbital plane around the Sun. This axial tilt is crucial because it affects how sunlight is distributed across the planet throughout the year.

During different times of the year, various parts of the Earth receive varying amounts of sunlight due to this tilt. For example, when the Northern Hemisphere is tilted towards the Sun, it experiences summer because it receives more direct sunlight, leading to warmer temperatures. Conversely, when the Southern Hemisphere is tilted towards the Sun, the Northern Hemisphere experiences winter due to receiving less direct sunlight.

This phenomenon is not related to the Earth's distance from the Sun, as Earth's distance does not change significantly enough to impact the seasons in conjunction with the axial tilt. The Earth's shape is largely spherical, and while it plays a role in climate and weather, it does not directly cause seasonal changes. Similarly, the speed of Earth's rotation contributes to the daily cycles of day and night rather than the annual changes that define the seasons.

Therefore, the tilt of Earth's axis is the fundamental reason why we experience different seasons throughout the year.