Odd One Out

Celestial objects

Activity overview

15 mins
Ages 5 – 7 , Ages 9 – 11

Science topics:

Space , Seasonal changes

Here are three celestial objects that your children should be familiar with. But how do they differ? This activity is great for promoting observation and discussion skills.

Run the activity

1. Show the three images above and ask everyone to come up with as many similarities and differences as they can. If they get stuck, prompt them to think about:

  • appearance
  • what they do
  • where they might be found

2. Then, everyone needs to decide which one is the odd one out and why. Encourage a reason for every answer and there is no wrong answer!

Background science

A celestial object is any natural object that can be seen in space. Stars, moons and planets are all examples of celestial objects.Those pictured are the Sun, the Earth and the Moon. They are all parts of our solar system. The solar system has the Sun, a star, at the centre. The Sun is a star because it generates its own heat and light. The eight known planets and their moons, as well as comets, asteroids and other space objects, all travel around the sun in circles known as orbits. 

The Earth is a planet which orbits the Sun, and the Moon is a natural satellite, which is an object that orbits a planet. The Sun is made from gas, whereas the Earth and the Moon are made mainly from rocks. Seen from space, the Earth's surface appears blue because most of it (71%) is covered in water.

These photos are taken from space and show that the Earth and Moon are spheres. Before we had access to these images, we knew that Earth was a sphere. Indeed, Greek philosophers wrote about the Earth being shaped as a sphere over 2,500 years ago.  

How do we know the Earth is not flat? 

  • travelling in one direction around the Earth brings a person back to where they started from; 

  • flying in a plane at a high altitude shows the horizon to be curved; 

  • the shadow of the Earth, as it moves across the Moon during a lunar eclipse, is observed to be a round shape; 

  • the bottom of a boat sailing out to sea disappears from view on the horizon before the top of the boat. 

The Earth is 12,756km in diameter, the Moon 3,475km and the Sun 1,391,016km. So the diameter of the Moon is slightly less than a quarter of that of Earth, whereas the Sun’s diameter is approximately 100 times bigger. 

Watch out for 

Children can think that the Earth is the biggest object within our Solar System because the Sun, Moon and other planets appear to be small from Earth. This is because we are looking at them from a distance. Many children are also surprised to learn that the Sun is a star.  

For a detailed guide to children’s misconceptions and a guide to questions to assess their prior knowledge look at these BEST resources.   

Take it further

Activities 

For young children they can learn about the Earth, Sun and Moon with this BBC Bitesize page. You will need to read it as a class or make a very simplified version for the children to read. 

You could read On the Moon by Anna Milbourne and Benji Davies or Our Stars by Anne Rockwell which gives the children information about space. 

For older children 

You could get children to consider the relative size of the Earth, Sun and Moon. Show a football and a tennis ball. Which would be the Earth and which the Moon? How far apart should they be? Ask the children to suggest the distance. Wrap a piece of string 10 times around the football (Earth) and that distance is where the tennis ball (Moon) would be orbiting.  If the Sun is approximately 100 times wider than Earth, its volume will be 1,000,000 times bigger than Earth. What would be needed to model the Sun? It’s width would be about as tall as a block of flats with 9 floors.  

Or if you used a beach ball to model the sun, what would be needed to model the Earth?  

This Royal Observatory activity uses fruit to compare the relative size of the different planets in our Solar System. The Ogden Trust have two scaled models- one compares the relative sizes of the planets using playdough and the other compares the distances between them. Two models are needed to look at scale in the classroom because it is really difficult to compare them both in one scaled model as NASA explains here.

Linked Explorify activities - our recommendations: 

Think about the appearance of the Moon with, Have you ever looked at the Moon and noticed how it appears to be different shapes at different times? and Black hole. Enjoy this What’s Going on? looking at Earth

Watch 

This BBC video looks at how we know the Earth is a sphere. This video compares the relative size of the Earth, Sun and Moon.

 

Image credits:

Earth via Nasa CC BY-NC

Sun via Nasa CC BY-NC

Moon via Nasa CC BY-NC