Hello everyone.

I'm so glad you've come to join me today.

I'm Mrs. Horan and I'm really looking forward to completing today's lesson with you.

Together we are going to be learning all about the different sizes of objects in space.

Today's lesson is part of the earth, sun, and moon unit.

The lesson is called "The relative sizes of the Earth, sun, and Moon", and we will be learning about the relative sizes of these objects.

The outcome for our lesson today is to describe and compare the sizes of the Earth, sun and moon.

This lesson builds on what you already know about the shape of earth and other objects in space and is part of our big learning question, how does the earth fit into the universe? These are the keywords that we're going to be focusing on today, earth, sun, moon, relative and scale.

Some of those will be familiar and some may be new, so we will take a closer look at them when they pop up in the lesson.

Here are some explanations of the keywords.

As I said, our new words will be explained as we come to them during the lesson, so you don't need to look closely at them now.

They're just here in case you need a reminder of anything later on and need to look back for a quick check.

Our lesson today is divided into three parts.

We'll start with the first part, how big is the sun? We know that our planet, Earth, and the sun are both objects in space.

There are many more objects in space, but let's focus on these two familiar ones for now.

How big do you think each of these objects is? Do you think one is larger than the other? Maybe you think they're around the same size? The sun is the largest object in our solar system.

It is much larger than earth and the moon.

It is bigger than all of the other planets and moons in the solar system too.

It doesn't look very big to us though because it is very far away.

It's so far away in fact that if we could get on a plane and fly there, it would take us 19 years to get there and if we ever did make it there, it would be so big, it wouldn't be possible to see all of it at once like we can from Earth.

The sun is so very big in fact that over one million earths could fit inside it.

This picture shows the relative sizes of earth and the sun.

The word relative is one of our keywords today.

When we talk about the relative size of something, it means its size in comparison or relation to other things.

So if we were thinking about the relative sizes of you and a spider, you would be pretty big.

If we were thinking about the relative sizes of you and an elephant though, you would seem rather small instead, can you see how teeny tiny the earth looks in that picture? This is actually how small it is compared to the sun.

If we could magically put the earth and sun right next to each other, then back up and look at them both, this is how they would look.

Is it what you expected or did you think that the earth wasn't quite so small compared to the sun? I know before I saw this picture I thought the earth would be much bigger in comparison.

It's quite surprising how our huge planet can look so tiny.

It makes you think about how very, very big the sun must be.

Because the size of the sun and earth relative to each other are accurate in this picture, we can say the sizes of the object in the picture are to scale.

Scale is another one of our keywords for today.

When we say things are to scale, we mean their relative sizes are accurate.

We can use scale to help us understand the size of very big or very small things.

The distance between earth and the sun in this picture is not to scale.

This means that it is not accurate relative to the size of the object.

So as we said, the sizes of the earth and sun compared to each other are accurate or correct in this picture, the distance between them is not though.

In reality, the sun is much, much further away from earth than it appears in this picture.

If the earth was actually that close to the sun, it would be far too hot for anything to survive and far too bright for us to see anything even if we could survive.

It is very hard to create pictures that show us both the relative size of objects in space and a relative distance from each other at the same time because of the huge, huge numbers involved, such a picture would have to be very, very big and the earth would probably look too small to see.

If we were creating a scale model of earth and the sun showing the relative sizes of each, we could use a basketball just like this one to represent the sun.

What do you think will be a good model for earth on this scale? So think about the picture we have just looked at with the relative sizes of the sun and earth and think about this basketball here and try to picture it.

The sun was this big, how big do you think the earth would be? So on this scale, a peppercorn or anything of a similar size would be a good model of earth.

There's a peppercorn on the screen there and I have one with me here.

As you can see, it looks pretty small in comparison to our basketball sun, doesn't it? Let's try something though.

I'm going to put our sun all the way over here.

Now let's see what happens if I move our peppercorn really close to the camera.

Now we can see it looks bigger than the basketball, so it looks bigger than our model of the sun.

Bring it back and we can see that actually it is much, much smaller.

This is exactly why the sun seems smaller to us than Earth does.

We are much, much closer to earth like we were much, much closer to that peppercorn minute ago.

So it seems bigger than the sun, which is really far away.

Let's try to check for understanding now.

See how we're getting on.

Which is the largest of these objects in space? Is it A, earth, B, the sun or C, the moon? Well done, it is B, the sun.

The sun is much bigger than both the moon and the earth.

Remember, it's so much bigger that we could fit over a million earths inside it.

Next question, if we use a beach ball to represent the sun, what would be a good model for earth on this scale? Do you think it would be A, a football, B, an egg, or C, a pea? Think about that picture we looked at with the relative sizes of the sun and earth again.

Which of these do you think would be the best size to represent the earth accurately to scale? It would be C, the pea.

The other two objects are too big.

Not to mention that the egg isn't a very good model for the earth because it isn't a spherical shape.

Time for you to try practise task and apply our new learning.

Close or cover one of your eyes and hold up your thumb like you're giving someone a thumbs up.

Move your thumb around until you've got it in a position where it completely covers the picture of the sun from your viewpoint, how is it that you can cover this image of the whole sun using just your thumb if your thumb is much smaller than the picture? I'd like you to think about how this could apply to what we know about the relative sizes of the earth and the sun.

Have a think and talk to a partner about your ideas.

Pause the video here for some thinking and discussion time and then come back when you're ready.

How did you do? Here is what Alex thought.

My thumb is smaller than the picture, but it is much closer to me so it looks bigger than the picture of the sun.

The earth is closer to us than the sun, so it seems much bigger to us even though it is actually smaller.

Did you have similar ideas to Alex? Let's take a look at the second part of our lesson now.

How big is the moon? So we know that the sun is much bigger than earth.

Compared to the sun and earth, how big do you think the moon is? Here's a picture of the moon and you've probably seen the real thing in the sky too.

How do you think it compares to earth or the sun? Bigger or smaller? Or do you think it's about the same size? The moon is smaller than earth.

Is that what you thought? This picture shows the relative sizes of earth and the moon to scale.

So just like the picture of the sun we looked at before, this picture shows us clearly how the size of the moon compares to the size of earth.

We can see it's smaller but it is not as small compared to the earth as the earth was compared to the sun.

This picture shows the relative sizes of earth and the moon to scale.

However, the distance between earth and the moon is not to scale in this picture.

It's actually much further than is shown here.

If the moon were actually that close to earth, then it would look really big in the sky at night.

The artists have just drawn them closer together so it is easier for us to get an idea of their relative size.

If we use the football to represent the earth, like this one here, the moon would be around the size of a tennis ball like this one here.

On this scale you can see that the earth is bigger than the moon, but the difference in size is not as large as the difference between the earth and the sun that we looked at before.

On the scale we used before where the sun is a basketball and the earth is a peppercorn and the moon would be the size of a full stop drawn on a piece of paper.

So here is our sun, here is our earth and here is our moon full stop I have drawn on some paper.

Can you see my moon from where you are? Probably not because it is so much smaller than our basketball sun.

In the sky, the sun and moon look like they're about the same size.

You can see this in the picture here.

The sun is on the left and the moon is on the right.

They do look very similar in size.

Why do you think they look like this? We've just seen with our model that the moon is much, much smaller than the sun.

So why do they look the same size to us? It's because the sun is much further away from us than the moon is.

Remember before we said it would take 19 years to get to the sun on a plane? Well, it would only take around three weeks to get to the moon if we could travel there by plane time for another check on our understanding.

Starting with the smallest, put these objects in order of size.

We have the earth, the moon, and the sun.

So starting with the smallest object, correct order is moon earth, sun.

Let's have a go at another practise task.

Sofia is looking at this photograph of the earth that was taken by an astronaut standing on the surface of the moon.

Sofia says, earth looks pretty small in this photo taken from the moon.

I think the moon must be larger than earth.

Do you agree with Sofia? Think about this, discuss it with a partner and explain why you agree or disagree.

Pause the video here to give this a go and come back when you are done.

Did you find it easy or tricky to put your thoughts about this one into words? Sofia's idea isn't correct.

Is that what you said? You might have thought, I do not agree because I know the moon is smaller than Earth.

It looks like the moon is bigger than earth because the photo is taken from the moon so it's close.

Earth is far away so it looks smaller.

That brings us to the third and final part of our lesson today.

Researching the size of objects in space.

It can be quite tricky to think about the size of spherical objects.

We can use a measurement called the diameter of a sphere to describe its size, the diameter is the longest possible length through the middle from one side of the sphere to the other, so on our football it would be all the way through the middle from the point on this side to the opposite point on the other side, you can also see the diameter labelled on the picture of the sphere there on the screen.

Astronomers make observations and calculations to estimate the diameter of sun, moon and earth.

They can't actually measure because there is no ruler or tape measure long enough, but they can work it out by looking carefully at the observations they have made.

The diameter of the moon is about 1/4 of the diameter of Earth.

Not exactly, but it is approximately around 1/4.

The diameter of the earth is around 12,742 kilometres and that seems incredibly big to me.

If that's the diameter of the earth, what do you think the diameter of the sun might be? It's definitely going to be a bigger number, but how much bigger? You might want to make a little note somewhere of your idea so you can remember it and refer back to it later.

You have made an estimate about the diameter of the sun.

You could find out how accurate you are by doing some research about the size of object in space.

Make sure you hang onto that note with your estimate on and you'll be able to see how close you were.

Let's have another quick check-in on how things are going.

Can you match the object to their diameters? We have a tennis ball, a pea and a beach ball on one side and diameters of one centimetre, 6.

5 centimetres and 40 centimetres on the other side to match them to.

Which object do you think has which diameter? Pause the video to have a quick try here.

How do you think you did? Let's take a look.

Tennis balls are around 6.

5 centimetres in diameter.

The pea was our smallest sphere with a diameter of only about one centimetre, and the beach ball was the largest sphere with a diameter of 40 centimetres.

Next question, what can we do to find out about the size of objects in space? Can we A estimate, B research or C, diameter? Great, we can carry out research to find out about the size of objects in space.

Time for our final practise task of the lesson, it comes in two parts.

First, do your own research to find out the approximate diameter of the earth, sun and moon in kilometres.

Make sure you look for their size and kilometres, not in miles, otherwise your relative sizes might not match up with each other.

As you're researching, think about this question.

Do all sources give exactly the same information? Why do you think this is? Pause the video here and go and do your initial research and come back and see how you did and get the second part of our task.

Welcome back, here are the measurements Lucas found.

The diameter of the sun is 1.

4 million kilometres.

The diameter of the moon is 3,500 kilometres and the diameter of Earth is 12,700 kilometres.

Did you find that all sources gave the same measurements? Andeep didn't, this is what he thought about the differences he saw.

I found that different websites provide different information.

Not everything is true on the internet.

Also, the measurements of objects in space are approximate.

For the second part of our task, you need to use your research to find a country that is approximately the same distance away from England as the diameter of the moon.

Lucas is helping us out here by reminding us of the diameter of the moon, which is approximately 3,500 kilometres.

Which country is approximately 3,500 kilometres away from England.

Look on a map or a globe at this distance.

This can help you to understand the relative of the moon.

Pause the video here and see what you can find.

How did you do? Let's see what Lucas and Andeep found out.

Lucas says that the diameter of the moon is 3,500 kilometres.

I found that the distance from England to Egypt is 3,884 kilometres.

Andeep said I looked on a map at the distance between England and Egypt.

I'm amazed that the moon is approximately the same distance as this across its diameter.

Did you find anything similar? Did you find any other countries that were approximately the same distance away from England as the moon is from Earth? We've come to the end of our lesson about the relative sizes of object in space, we've packed a lot in today.

Let's recap on our key learning from the lesson.

The sun is much bigger than earth, and Earth is bigger than the moon.

Around one million Earths could fit inside the sun.

The moon is around a quarter of the size of earth.

We can use pictures drawn to scale to help us understand the relative size of very large object in space.

Thank you for coming to join me today and for your hard work and critical thinking.

I've really enjoyed finding out about the sizes of the earth, sun and moon with you, see you again next time.