What it shows
A solar eclipse happens when the Moon passes between the Sun and the Earth and its shadow falls on the Earth. The dark inner shadow (umbra) covers only a small patch where the eclipse is total, and the lighter outer shadow (penumbra) covers a wide area that sees a partial eclipse.
The science
The Sun is much wider than the Moon, so light from its different parts reaches the Moon from slightly different directions. Behind the Moon there is a cone where all sunlight is blocked, the umbra, and a wider zone where only part of the Sun is blocked, the penumbra. The umbra narrows with distance and only just reaches the Earth, which is why a total eclipse is seen along a thin path no more than about 250 kilometres wide while a partial eclipse is seen over a much larger region.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A large ball or globe for the Earth
- A small ball about a quarter the size for the Moon on a stick
- A small bright torch or a clear-bulb lamp for the Sun
- A dark room
- White paper to catch the shadow
- Labels
Safety
For this project: Never look at the real Sun during an eclipse without proper eclipse glasses; the model is safe to look at.
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.
Step 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 place the lamp at one end of a table as the Sun.
Stand the globe about a metre from the lamp.
Hold the Moon ball between them, about 10 centimetres from the globe, in line with the lamp.
Look at the shadow on the globe: a small dark centre and a faint wider ring around it.
Hold a sheet of white paper where the globe is and move the Moon closer and further to see the dark centre shrink and grow.
Label the dark centre umbra and the faint ring penumbra on a drawing.
Move the Moon slightly above the line so the shadow misses the globe, and explain why eclipses do not happen every month.
Mark on the globe where India is and show a path of totality crossing it.
What you should see
A clearly visible two-part shadow on the globe, and a drawing that labels umbra, penumbra, total and partial eclipse zones.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What is the order of Sun, Moon and Earth in a solar eclipse?
Sun, then Moon, then Earth.
02Why is a total solar eclipse seen only in a narrow path?
The umbra is a narrow cone that barely reaches the Earth.
03Why is there not an eclipse every new moon?
The Moon's orbit is tilted about 5 degrees, so its shadow usually misses the Earth.
04Why can a small Moon cover the large Sun?
The Sun is about 400 times wider but also about 400 times further away, so they look the same size.
Take it further
Move the Moon ball further from the globe, or use a smaller one, so the umbra stops short of the globe; this shows an annular eclipse, where a ring of Sun stays visible.
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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