The document discusses the causes of seasons. It explains that seasons are not due to variations in Earth's distance from the sun, as some believe, but are instead caused by the tilt of Earth's 23.5 degree axis. This tilt results in changes in the amount of incoming solar radiation (insolation) and the angle at which the sun's rays strike different locations throughout the year, causing the seasons to change. Specifically, when a hemisphere is tilted toward the sun it experiences summer, and when tilted away it experiences winter.