Axial tilt, also known as obliquity, refers to the angle at which a planet's axis is tilted in relation to its orbit around the Sun. For Earth, this tilt is approximately 23.5 degrees. This tilt is responsible for the changing seasons, as different parts of the planet receive varying amounts of sunlight throughout the year. The axial tilt of a planet can change over long periods due to gravitational interactions with other celestial bodies. For Earth, this tilt can vary between 22.1 and 24.5 degrees over a cycle of about 41,000 years. This variation can influence climate patterns and contribute to long-term climate changes.