Astronomy Practice Exam

The changing seasons on Earth are primarily caused by the tilt of the Earth's axis. The Earth is tilted at an angle of approximately 23.5 degrees relative to its orbital plane around the Sun. This axial tilt means that as the Earth orbits the Sun throughout the year, different parts of the Earth receive varying amounts of sunlight, leading to seasonal changes.

During summer in one hemisphere, that hemisphere is tilted towards the Sun, resulting in more direct sunlight and longer days, which warms the region. Conversely, during winter, the hemisphere is tilted away from the Sun, leading to less direct sunlight, shorter days, and cooler temperatures. Spring and fall are transitional periods when the tilt is such that both hemispheres receive roughly equal amounts of sunlight.

The other options do not directly cause the seasons. Although the distance of the Earth from the Sun varies slightly due to its elliptical orbit, this variation does not have a significant impact on seasonal changes. The Moon's orbit affects tides and other phenomena but does not influence the seasons. Similarly, while the rotation of the Earth on its axis results in day and night, it does not account for the seasonal variations that arise from the tilt and position of the Earth in its orbit around the Sun.