Teacher guide · Grades 5–8 · 12–15 minutes

Test a No-Tilt Earth

Test a counterfactual directly: keep the two Earth orbit positions fixed and change only axial tilt. Suggested teacher-led activity; not classroom-tested.

Learning goal and materials

Explain how Earth's axial tilt changes sunlight angle and daylight duration at matching north/south latitudes, and why distance alone cannot explain opposite seasons.

Provide this worksheet, pencil, a small marked foam globe (Earth), fixed cool LED lamp (Sun), and room for two opposite orbit positions. A teacher-drawn diagram is an alternative.

Prediction → evidence → reasoning

Prediction · 3 min. Ask: if Earth's axis were upright (zero tilt), would northern and southern summers still occur at opposite times? Record a claim before observing.
Control · 4 min. At two opposite orbital positions, keep the globe tilted about 23.5° and the axis pointing in the same direction in the room. Compare noon-light direction and the marked latitudes' paths through the illuminated half during one daily turn.
Zero tilt · 4 min. Repeat with the globe upright, without moving the lamp or changing the orbit points. Compare the hemispheres again. Change only axial tilt.
Reasoning · 3–4 min. Have pupils record two observations and explain which variable produced the strong opposite seasonal pattern.

Side-on schematic of the orbital plane; distances, sizes and the axis-angle drawing are not to scale. The tilted axes stay parallel at the two positions. A real model should show axial tilt relative to the orbit's perpendicular axis.

Safety: The teacher controls a cool LED lamp; never look directly into strong light, use a hot bulb or substitute the real Sun. Keep the globe out of the observer's shadow. The small lamp approximates sunlight and cannot simulate climate.

Expected explanation · hypothetical example, not pupil evidence

At real tilt, the favored hemisphere switches between opposite positions as the globe maintains its axis direction. At zero tilt, neither hemisphere leans toward the lamp at either stop; the strong opposing sunlight/daylight pattern disappears. Earth's slightly elliptical real orbit still changes incoming solar energy modestly for both hemispheres at once. No model here predicts constant temperatures or real weather.

Scientific basis: NASA Earth Facts — https://science.nasa.gov/earth/facts/ ; NASA Milankovitch Cycles — https://science.nasa.gov/science-research/earth-science/milankovitch-orbital-cycles-and-their-role-in-earths-climate/ . The physical demonstration is conceptual, not a measured classroom outcome.

Student worksheet · Grades 5–8

Would the Seasons Still Oppose Each Other Without Tilt?

Name:Date:

1. Claim / prediction — If Earth's axis had zero tilt, would the Northern and Southern Hemispheres still have strong opposite seasonal sunlight patterns? Explain your prediction.

2. Evidence — Use a cool LED lamp and globe or the teacher's drawings. Keep the lamp and two Earth positions fixed. Change only axial tilt. Record observations instead of guessing temperatures.

Axial tilt	June position: which hemisphere receives more direct light?	December position: which hemisphere receives more direct light?
Real Earth · 23.5°
Hypothetical Earth · zero tilt

Evidence: describe two observations from your experiment.

3. Reasoning — Why does the actual Earth have northern and southern seasonal patterns that oppose each other? What changed at zero tilt?

4. Exit ticket — Earth is nearer the Sun in early January. Why is it winter in the Northern Hemisphere then?

The globe-and-lamp model is not to scale. It does not predict real weather, atmosphere or surface conditions. Zero tilt would not mean perfectly constant temperatures.