Final answer:
The Earth's rotational axis is tilted 23.5 degrees with respect to an imaginary line perpendicular to the plane of its orbit around the sun. This tilt is responsible for the changing seasons on Earth.
Step-by-step explanation:
The Earth's rotational axis is tilted 23.5 degrees with respect to an imaginary line perpendicular to the plane of its orbit around the sun. This tilt is responsible for the changing seasons on Earth. When the Northern Hemisphere is tilted towards the sun, it experiences summer, while the Southern Hemisphere experiences winter.