BBC Sky at Night - UK (2021-08)

What you’ll need

X Nine polystyrene balls of different diameters for the Sun and planets;

we opted for the Sun at 11cm; Mercury at 2cm; with Venus, Earth and

Mars at 3cm; Jupiter at 6cm; and Saturn, Uranus and Neptune at 4.5cm.

X Cocktail sticks or small wooden skewers – we used these to stick the

planets into the ground; water-based paint for each planet.

X Small stone chips and a piece of clear plastic or card to create the

asteroid belt – we used a piece measuring 33cm x 15cm and made

it by sticking two pieces together with clear tape.

X A long tape measure – if you are measuring by yourself, peg the

end of the tape to the ground with a barbecue skewer.

W

e have all seen diagrams

showing the planets of our

Solar System orbiting the Sun.

Sometimes their relative sizes

are shown, but it is impossible

to depict the space between

them – the orbital distances of each of them from

our central star. Our Solar System is huge and the

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using scale models helps us to visualise this. As the

distances are so big, it’s almost impossible to have

both accurate planet sizes and distances in one scale

model: if we scaled the distances based on the Sun’s

size we used in this model, Neptune would be half

a kilometre away! This is not something you can

squeeze into most gardens.

For this fun project, we are creating a model that

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garden or park. The radius of our Solar System has

been scaled down to 10m. If our Sun and planets were

at the same scale, the Sun would have a diameter

of 3cm, but Mercury would be a microscopic 0.1mm,

Earth 0.2mm and the largest planet, Jupiter, just

3mm. Obviously we can’t replicate that for our model.

Instead, we’ll be using polystyrene balls of different

sizes to show that the planets vary in diameter, but

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other or to the distances. We’ll place our planets in a

straight line, but they would really extend out by 10m

in all directions from our star.

The distance between the Sun and the Earth is

150,000,000km; this is 1 Astronomical Unit (AU). To

make the maths simple when calculating the distances

for our model, begin by working with a scale of 1 AU to

1 metre. With Neptune at 30 AU, it means the model

would be 30m, which is still larger than most gardens.

Indeed, we only had 10m to work with. But as this is

three times smaller, we got the distances in metres for

each planet down to a manageable scale by dividing

the AU for each planet by three. You can adapt this

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The distances from the Sun for each of the

planets are in our downloadable table (see below for

instructions). We’ve also included the inner and outer

edge of the asteroid belt. We painted our Sun and

planets an appropriate solid colour so they would

show up better in photos, but you can add surface

features and the rings of the four giant planets.

The end result will give you an invaluable insight

into the distances in our planetary neighbourhood.

DIY ASTRONOMY

Practical astronomy projects for every level of expertise

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74 BBC Sky at Night Magazine August 2021

Mary McIntyre

is an outreach

astronomer and

teacher of

astrophotography

Make a scale model of the Solar System

Build a model in your garden to reveal the spacing between our planetary neighbours

FAMILY

FRIENDLY

PROJECT

Compare views

from the Sun

outwards (left),

and back from

Neptune (right)

Download a conversion table (from Astronomical Units

to metres) to show the spacing of each Solar

System body on the model. See page 5 for instructions

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