1. Title: Relative Sizes and Distance in the Solar System: Introducing Powers of Ten

Again from a very young age children seem to be aware of the Sun and Moon in the sky. They may have songs or poems that the Sun comes out in the day and the Moon comes out at night as they go to bed. The Sun frequently appears in the birthday cards they draw for family members and in their paintings. As children get older they may observe that the Moon is still up during the day. We can use a Moon phase resource to explain the changing appearance and visibility of the Moon.

Ask the children which do they think looks bigger in the sky, the Moon or the Sun? Use observation, prediction and have a discussion. Do this when the Moon is full or near full and tell them to look for the Moon over the next few nights at bedtime, you can look up the Moon phases on www.heavens-above.com

Think: Get children to look at the Sun and Moon and compare their relative sizes.
H&S: warn the children never to look directly at the Sun and never, ever through binoculars or a telescope, as permanent eye damage would result.
Actually, the Sun’s diameter is 400 times bigger than the Moon’s diameter but by coincidence the Sun is 400 times further away and this makes them seem almost the same size in the sky! This coincidence allows a total eclipse of the Sun to happen when the Earth, Moon and Sun are all lined up correctly, with the Moon coming between Earth and the Sun.
As children get older, in KS2 for example, we can start to build scale some models to help them understand the size and distances in the Solar System.
* UK Primary schools have Foundation (P1 & P2), Key Stage 1 (P3, P4) and KS2 (P5, P6 & P7)
Let’s build some models!

1.1 Activity 1: Relative Sizes in the Solar System

Choose a small beachball or football to represent the Sun, around 24 cm across.

Now give them the answer (refer to Table): the gas giants, Jupiter and Saturn, are about 2 cm across, and the terrestrial planets about 2mm across, and Uranus and Neptune in between. See Table for more exact figures.  Now make them!

In this activity we are going to get the children to make scale size models of the Sun and planets to get some idea of their relative sizes. We could give them a table of information to read but they tend to get more of an impact and a wow factor when they finally put all the planets together in a row!

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  You will need modelling clay
  
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  30cm rulers
  
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  Planet name labels – supplied at end of this document
  
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  ball - 24cm approx (1 to 3 needed)
  

The third column in grey is merely to show the scale distances these spheres would need to be placed apart if they were laid out on the ground on the same scale as the planet sizes.

10 times smaller than Jupiter and Saturn) which in turn are around 10 times smaller than the Sun etc.)

Table gives the correct results, but we haven't quite got there yet.)

In this activity we will construct a scale model of the distances between the Sun and planets and we will not worry too much about their relative sizes for now.

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  You will need modelling clay
  
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  10m of string
  
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  scissors
  
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  1m rule/tape measure
  
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  Planet name labels – supplied at end of this document - Moon not needed here
  
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  ball
  

We can tell the children all about the vast distances but getting them to think relatively may be more helpful. For example, it is 150,000,000 km (150 million km) from the Sun to Earth, what if we used this distance to compare the distance of other bodies? Well, we do and this special distance is called 1 Astronomical Unit or AU.

From this we can say Mars is a distance of 1.52 AU from the Sun, Jupiter 5.20 AU. Neptune is a distance of 30 AU from the Sun (30 times the Sun-Earth distance unit) and so on.

From just beyond Neptune’s orbit, from approximately 40AU to approximately 60 AU is the Edgeworth–Kuiper belt.

Even more distant, the Oort cloud is located at approximately 1,000 – 200,000 AU. The outer limit of the Oort cloud defines the boundary of the Solar System and the region of the Sun's gravitational dominance. c

Let’s finish with a really simple scale and see if you can see a pattern in the relative sizes:

If the Sun were represented by a sphere 23-24 cm diameter:

Then make the 4 innermost planets very small: Mercury 1mm, Venus 2mm, and Earth 2.4mm and

Mars 1.5mm

Jupiter 2.4 cm

Saturn 2cm

Uranus and Neptune 1cm each

Tiny Pluto 0.5mm

If we can see and only remember from this exercise that (approximately):

1 the 4 innermost planets are 1/100^th the size of the Sun;

2 the two biggest planets Jupiter and Saturn are approximately 1/10^th the size of the Sun

3 the 4 innermost planets are 1/10^th the size of the 2 big planets.

Also

For children fascinated by space flight;