The main reason for the changing seasons on Earth is the axial tilt of the planet as it orbits the sun. Earth is tilted at an angle of approximately 23.5 degrees, which affects the intensity and duration of sunlight received at different latitudes throughout the year. During summer in one hemisphere, that side of Earth is tilted toward the sun, resulting in longer days and higher temperatures. Conversely, during winter, that hemisphere is tilted away from the sun, leading to shorter days and cooler temperatures. This axial tilt creates the seasonal variations experienced across the globe, profoundly affecting ecosystems and human activities.