Students are often confused about the cause of seasons on the Earth, assuming that the cause is changes in the distance to the Sun, not changes to the length of the day and the angle of incidence of the Sun’s light. The Ringworld provides a way to explore causes of seasons.
At first it seems as if Ringworld wouldn’t have seasons. After all, on Ringworld, the length of day is constant. While this could be changed by adjusting the distance between the shadow squares (note that the shadow squares aren’t in orbit around the sun either - they’re connected by improbably strong wires and are spinning faster than necessary to stay in orbit), it’s hard to imagine getting a useful amount of day length change over a long period and the mechanism to do so would be pretty complicated. Changing the distance to the sun is also possible (but see what happens two slides further), but since the Ringworld rotates with a period of 8 days or so, seasons would be very short. And it would seem that the angle of incidence of the Sun’s light would have to be constant – but that turns out not to be the case.