What it shows
A tiny hole makes an upside-down image of the Sun on a screen. During a partial eclipse the image shows a bite taken out of the disc, so you can watch without looking at the Sun.
The science
Light travels in straight lines, so rays from the top of the Sun cross at the hole and land at the bottom of the screen. This flips the image, which also keeps its shape. A longer box gives a bigger but dimmer image, because the same light spreads over more area.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A long cardboard box or a tube, about 60 cm
- Aluminium foil, a pin and tape
- A sheet of white paper for the screen
- Black paper to cover the inside
- Scissors and a marker
- A ruler
Safety
For this project: Never look straight at the Sun, not even through the pinhole, sunglasses or a telescope. Stand with your back to the Sun, and an adult must supervise.
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.
Cut a square window at one end of the box and tape foil over it.
Make a small clean hole in the foil with a pin, about 1 mm wide.
Tape white paper on the inside of the opposite end of the box as the screen.
Cut a viewing slot on the side near the screen so you can look at the paper, not the Sun.
Colour the inside with black paper to cut stray light.
On a sunny day, point the pinhole end towards the Sun by checking that the box shadow is smallest.
Look through the slot at the round bright image on the screen and measure its diameter.
On eclipse day watch the circle change shape and sketch it every ten minutes.
What you should see
A round image of the Sun about 5 mm wide for each 50 cm of box length, and during a partial eclipse the same image shows a growing and shrinking bite.
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 the image upside down?
Rays cross at the pinhole.
2Why is it safe?
You look at a screen and never at the Sun.
3What happens if the hole is larger?
The image becomes brighter but blurrier.
4What is a partial eclipse?
The Moon covers only a part of the Sun’s disc.
Take it further
Watch dappled sunlight under a tree during a partial eclipse and explain why the spots become crescents.
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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