Final answer:
Earth's seasons are caused by its 23.5° axial tilt, which alters the intensity and angle of sunlight received as it revolves around the Sun, leading to variations in heating and daylight across the year.
Step-by-step explanation:
Earth experiences seasons due to the tilt of its axis, which is inclined at 23.5° relative to the normal of its orbital plane around the Sun. This axial tilt affects the intensity of the sunlight that reaches different parts of the Earth throughout its revolution around the Sun. During the summer solstice, the hemisphere tilted towards the Sun receives more direct sunlight, leading to longer days and increased heating.
Conversely, during the winter solstice, the Sun's rays strike the inclined hemisphere at a greater angle, resulting in shorter daylight hours and less intense heating. The equinoxes mark the transitional periods when the Earth's axis is not tilted towards or away from the Sun, providing roughly equal amounts of daylight and night.