Why We Have Seasons

Activities to try

1. 1

   Drive Earth through a year with a fixed-direction tilt

   Why it works: Because the tilt direction is fixed, orbital position decides which hemisphere leans sunward; that hemisphere gets more direct (concentrated) sunlight and longer days — that is summer.

   1. Move a tilted Earth around the Sun, keeping the axis pointing the SAME direction throughout the orbit (it does not swivel to follow the Sun).
   2. At each position, notice which hemisphere leans toward the Sun and read off the angle at which sunbeams strike a chosen city.
   3. Compare June and December for the same northern-hemisphere city: in June the beams come down steep (sun high) and pack into a tight bright patch; six months later they slant in low and spread the same light over a much larger patch (about twice as large at 40°N, and over three times as large at UK latitudes, measured at midday), so each bit of ground gets less.
   4. Also watch the day-length bar change between the two dates and note both directness and longer days make summer warmer.
   5. Optionally, orbit the viewpoint around a 3D model to confirm the axis never changes direction — only its relationship to the Sun changes.
2. 2

   Torch and squared paper: direct vs slanted light

   Why it works: The angle of sunlight, not the distance, controls how concentrated the energy is on the ground — slanting spreads the same light over more area so each part heats less.

   1. In a dim room, PREDICT with a reason: using the same torch at the same (constant) distance, will the lit patch be brighter, dimmer, or the same when shone straight down versus at a low slant (tilted well away from straight down)?
   2. Commit to your prediction, then shine both ways onto squared paper and count how many squares each lit patch covers.
   3. Observe that the slanted beam spreads over more squares (the lower the slant, the more squares), so each square is dimmer — the same light spread thinner.
   4. Map this onto seasons: higher, more direct summer sunlight (closer to overhead, though outside the tropics the Sun is never directly overhead) is concentrated and warming; low, slanted winter light is spread out and weaker. Treat the torch as a stand-in for the Sun.
3. 3

   Confront the distance idea with two killer facts

   Why it works: A distance model predicts both hemispheres share one season and that closest means hottest; both predictions are false, so distance cannot be the cause — tilt-and-directness is.

   1. First explain in your own words why you think we have seasons, before seeing any answer (surface your current idea).
   2. Test a 'seasons = distance' idea: if Earth simply moved nearer and farther, both hemispheres would brighten and dim TOGETHER — yet when the UK has winter, Australia has summer. Does distance explain opposite seasons at the same instant?
   3. Consider that Earth is actually slightly CLOSEST to the Sun in early January, during northern winter. If nearness caused summer, why isn't January our hottest time?
   4. State which model survives both facts (tilt/directness) and which cannot (distance).
   5. Optional: role-play with an 'astronomer' who asks you to explain seasons, then poses these two facts and guides you toward tilt.