What it shows
A lunar eclipse happens at full moon when the Earth moves between the Sun and the Moon and the Moon passes through the Earth's shadow. The Moon does not go fully black because the Earth's atmosphere bends red sunlight into the shadow.
The science
At full moon the Moon is on the far side of the Earth from the Sun. If the three line up, the Moon passes through the Earth's umbra and goes dark. The Earth's atmosphere refracts some sunlight into the shadow, and because the air scatters blue light away, the light that reaches the Moon is mostly red, like every sunset on Earth at once. Lunar eclipses are visible from the whole night side of the Earth, unlike solar eclipses.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A globe or a large ball for the Earth
- A small white ball on a stick for the Moon
- A torch for the Sun
- A clear glass of water with a drop of milk to act as the atmosphere
- A dark room
- A red cellophane sheet
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.
Darken the room and set the torch at one end of the table.
Place the globe in the middle and hold the Moon ball on the far side, in line with the torch.
Show that the Moon ball is in the globe's shadow and looks dark.
Raise the Moon slightly out of line so it is lit again, and explain why most full moons have no eclipse.
Hold the milky glass of water in front of the torch and shine the beam through it onto white paper; note the reddish tint.
Tape the red cellophane over part of the torch and place the Moon in the shadow again; a dim red Moon shows the real effect in a simple way.
Draw the Sun, Earth, Moon line and the Earth's shadow cone, and mark the Moon inside it.
Write why the eclipse is visible from the whole night side of the Earth.
What you should see
A model where the Moon ball goes dark inside the globe's shadow and takes on a red tint, with a drawing that places the three bodies correctly.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1At which phase does a lunar eclipse happen?
Full moon.
2Why does the Moon look red?
The Earth's atmosphere bends red sunlight into the shadow while scattering blue light away.
3Who can see a lunar eclipse?
Everyone on the night side of the Earth at that time.
4Is it safe to watch a lunar eclipse with bare eyes?
Yes; the Moon is only reflecting sunlight.
Take it further
Look up the next lunar eclipse visible from India and plan to time the stages.
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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