Science and Technology K–6 · Year 6

Torch on graph paper: why low winter sunshine heats less

Science understanding: Earth and space sciences

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

A beam of sunlight arriving at a low angle spreads over a larger area of ground, so each square metre receives less energy; together with shorter days this, not Earth's distance from the Sun, makes winter colder than summer.

What you need

a torch with a cardboard tube 5.0 cm across and 15 cm long taped over the front to give a narrow, even beam
centimetre grid paper on a clipboard
a protractor and a ruler
a pencil
a book stack to hold the torch still
the Sydney noon Sun heights from the shadow-stick investigation (79.6 degrees in December, 32.7 degrees in June)

How to do it

Hold the torch so its beam hits the grid paper straight on (90 degrees), with the end of the tube 10 cm from the paper. Trace the lit patch and count the squares, counting a square that is more than half lit as one.
Tilt the clipboard so the beam strikes the paper at 60, 45, 30 and 15 degrees, keeping the tube end 10 cm from the centre of the patch. Trace and count each patch.
Record the area at each angle and describe how bright the patch looks.
Work out the fraction of the straight-on light each square receives: area at 90 degrees / area at the angle.
Compare each fraction with the fraction the live model gives for the same angle.
Use the Sydney noon Sun heights to compare a square metre of playground in December and in June, and add the effect of day length.

What you should see

The patch stretches into an ellipse as the angle drops and looks dimmer. A parallel beam 5.0 cm across would cover 19.6 square centimetres straight on, 22.7 at 60 degrees, 27.8 at 45, 39.3 at 30 and 75.9 at 15, because area = straight-on area / sin(angle). A torch beam spreads a little beyond the tube, so the counted patches are larger, but each patch divided by the straight-on patch still comes close to 1 / sin(angle); edge squares cause small differences. At Sydney's noon Sun each square metre of level ground gets 0.98 of the straight-on sunlight in December (79.6 degrees) and 0.54 in June (32.7 degrees), 1.8 times as much in summer. Adding the longer December day, the sunlight reaching a square metre of level ground at the top of the atmosphere above Sydney is 44.2 MJ on the December solstice and 16.2 MJ on the June solstice, 2.7 times as much; Earth being about 3 percent closer to the Sun in December than in June contributes only about 7 percent of that.

What changes

What you change: angle at which the beam strikes the surface
What you measure: area lit (squares) and brightness
What you keep the same: same torch and tube
10 cm from tube to patch centre
same grid paper
room lighting

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Summer is hot because Earth is closer to the Sun.
The Sun is the same height at noon all year.
A slanted beam carries less light in total (it carries the same light spread over more ground).

Safety card

Low riskLearners carry it out

Hazards

torch shone into eyes

Controls

beam pointed only at the paper

Note

Risk assessment before the lesson using Primary RiskAssess or the school's own template.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K-6 Syllabus (2017), current, taught until 2026; a Stage 2 outcome, because the nearest NSW content is the Stage 2 content on the Earth and the Sun ('identify the Sun as a major source of energy' and 'investigate how the Earth's rotation on its axis causes regular changes including night and day'), and neither the Stage 3 content under ST3-10ES-S, which is the planets of our solar system and sudden geological and extreme weather change, nor the 2024 Stage 3 content covers the seasons, Earth's tilt or the height of the Sun; code read from the syllabus document on 22 September 2026ST2-10ES-S
Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-1WS-S
Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-DAT-01
Australian Curriculum v9AC9S6U02AC9S6I03AC9S6I04

Sources

The pages the author read to write this activity.

All Concept Studio activities