Seasons: Thermochromic globe

Attach thermochromic plastic to a globe to show that temperature in the UK depends on whether our hemisphere is tilted towards or away from the Sun.

Apparatus and Materials

• World globe
• Filament lamp (or electric heater)
• Self adhesive thermochromic plastic

Preparation

Cut the thermochromic plastic into a strip and place it vertically on the globe next to the UK. Set the lamp-globe distance to ensure the thermochromic plastic strip shows a range of colours.

Procedure

1. Rotate the base of the globe so that the northern hemisphere is tilted directly towards the lamp (summer in the UK)
2. Switch on the lamp and highlight the changing colours of the thermochromic plastic (counter-intuitively lower temperature is indicated by red and higher by blue).
3. Switch off the lamp and rotate the base of the globe so the nothern hemisphere is tilted directly away from the lamp (winter in the UK). Emphasise that you have not changed the lamp-globe distance.
4. Switch the lamp back on.

Discussion prompts

• When the northern hemisphere is tilted away from the Sun is it summer or winter in the UK?
• What season is it south of the equator?

Teaching Notes

This demonstration tackles the common misconception that winter happens because the Sun is further away. Compare the UK (55°N) to a similar latitude south of the equator (eg Bouvet Island in the South Atlantic at 54°S) to emphasise that summer in the northern hemisphere corresponds to winter in southern, and vice versa,

Explain that you are turning the globe around for convenience. The direction in which the Earth’s rotation axis points doesn't really swap between summer and winter. Which hemisphere is leaning towards the Sun changes because of the Earth’s annual journey around the Sun.

Learning outcome

Students identify corresponding seasons for northern and southern hemispheres.