Answer: Earth's tilted axis
Explanation: The changing of seasons throughout the year is caused by Earth’s tilted axis. The Earth’s axis is tilted at an angle of about 23.4 degrees. As the Earth orbits around the Sun, different parts of Earth receive more solar energy than others, which causes the seasons. When the North Pole tilts toward the Sun, it’s summer in the Northern Hemisphere. And when the South Pole tilts toward the Sun, it’s winter in the Northern Hemisphere.