What it shows
The same beam of light spread over a larger area heats each square less. Sunlight arrives at a slant in winter and spreads thin, which is the main reason winter is cold, not the small change in distance from the Sun.
The science
The Sun's energy comes in a beam of fixed power. Aimed straight down, the beam covers a small patch and each square centimetre receives a lot of energy. Aimed at an angle, the same beam stretches across more squares, so each square gets less. Because the Earth's axis is tilted, the Sun is high in summer and low in winter at any place away from the equator, and the low winter Sun also stays up for fewer hours.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A torch with a narrow beam
- A sheet of graph paper or a hand-drawn centimetre grid
- A protractor
- A ruler
- A dark room
- Optional: a thermometer and a black card
Safety
This project uses safe, everyday materials. Still, read the rules below with a parent before you start.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
In the dark room, hold the torch 20 centimetres straight above the grid, pointing down at 90 degrees.
Trace the lit patch and count the squares inside it.
Keep the torch at the same distance but tilt it to 60 degrees using the protractor; trace and count again.
Repeat at 30 degrees; the patch becomes a long oval.
Make a table of angle against number of squares lit.
Divide 100 by the number of squares to get a "brightness per square" value for each angle.
If you have a thermometer, tape it under black card and time how long each angle takes to raise the reading by 2 degrees.
Write a conclusion linking the low winter Sun to the cold season.
What you should see
Square counts that roughly double from 90 to 30 degrees, showing each square gets about half the light, and slower warming at low angles if the thermometer is used.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why is winter colder?
The Sun is lower, so its light is spread over more ground and the days are shorter.
2Is the Earth closest to the Sun in summer?
No; the Earth is actually nearest the Sun in early January, so distance is not the cause of seasons.
3What causes seasons?
The tilt of the Earth's axis, about 23.5 degrees.
4Why is it hot at the equator all year?
The Sun is always high there, so the light is concentrated.
Take it further
Measure the noon Sun angle in your town in June and December with a shadow stick and compare it with your torch results.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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