What astronomical phenomenon causes the seasons to change on Earth?

The changing of the seasons on Earth is primarily caused by the tilt of the Earth's rotational axis. The Earth is tilted at an angle of about 23.5 degrees in relation to its orbit around the Sun. This axial tilt means that as the Earth revolves around the Sun throughout the year, different parts of the planet receive varying amounts of sunlight at different times.

During summer in the Northern Hemisphere, that half of the planet is tilted toward the Sun, resulting in longer days and more direct sunlight, leading to warmer temperatures. Conversely, during winter, the Northern Hemisphere is tilted away from the Sun, causing shorter days and less direct sunlight, which results in cooler temperatures. The Southern Hemisphere experiences the opposite seasonal changes concurrently.

While the revolution around the Sun is also a crucial factor in defining the yearly cycle of seasons, it is the axial tilt that determines the intensity and distribution of sunlight that leads to the seasonal changes we experience. The rotation of the Earth, which affects day and night, and moon phases, which influence tides, do not significantly impact the season change. Thus, the tilt of the Earth's rotational axis is the correct answer to the question about the astronomical phenomenon responsible for the changing seasons.