What it shows
Stars seem to form patterns called constellations. Cups with pinholes in the right pattern throw those patterns onto a dark wall, so a child learns to recognise Orion, the Great Bear, Cassiopeia and others before finding them in the real sky.
The science
Light travels in straight lines. Each pinhole lets through a narrow beam, and on the wall the beams land in the same arrangement as the holes, only bigger, so the cup acts as a simple projector. Making bigger holes for brighter stars copies the way constellations really look. The stars in a constellation are not near each other in space; they only look close from the Earth.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Seven paper or plastic cups
- A pin and a thicker needle
- A torch that fits the cup mouth
- Printed star maps of seven constellations
- Tape
- A dark room with a plain wall
Safety
For this project: An adult should make the holes; pins are sharp. Never shine the torch into anyone's eyes.
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.
Choose seven constellations, for example Orion (Mriga), the Great Bear (Saptarishi), Cassiopeia, Leo, Scorpius, the Pleiades (Krittika) and the Southern Cross.
Tape a printed map of one constellation to the bottom of each cup.
Prick a hole at each star with the pin, and use the thicker needle for the brightest stars.
Remove the paper and write the constellation name on the side of the cup.
In a dark room, push the torch into the cup mouth and point the base at the wall.
Move closer and further until the pattern is sharp and compare it with the map.
Quiz a friend: project a pattern and ask them to name it.
On a clear night, use the cups to find the same patterns in the real sky.
What you should see
Seven cups that each throw a recognisable star pattern on the wall, with brighter spots for brighter stars.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a constellation?
A pattern of stars as seen from the Earth, given a name.
2Are the stars in a constellation close to each other?
No, they are at very different distances; they only look grouped.
3Which constellation is called Saptarishi in India?
The Great Bear, Ursa Major.
4Why do we see different constellations in different months?
The Earth moves round the Sun, so the night side faces different parts of the sky.
Take it further
Make a cup for the Pole Star and the pointer stars of the Great Bear and use it to teach how to find north.
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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