Hello there, young scientists.

It is wonderful to have you joining me today.

I'm Mrs. Horan, and I'm really looking forward to getting stuck into today's learning with you.

Together, we are going to be learning all about scientific ideas about space and how they have changed over time.

Today's lesson is part of the Earth, Sun and Moon unit.

This lesson is called Scientific Theories from the Past, and we will be learning about how scientists have improved their understanding of the solar system over time.

The outcome from our lesson today is to describe how scientists from the past have helped us to learn about the solar system.

Today's lesson builds on what you already know about the solar system and how objects in the solar system move in relation to each other.

The learning in this lesson 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, evidence, theory, solar system, geocentric, and heliocentric.

Here are some explanations of the keywords.

I will explain these words 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 two parts.

Let's get stuck in with the first part.

Developing theories.

Take a really good look at this picture.

This is a closeup picture of a living thing.

Do you think it's a plant or an animal? What evidence do you have to support this idea? You're probably feeling pretty confident about it, but what is it about the picture that makes you so sure? The word evidence is one of our keywords for today.

Evidence is information that helps us to prove if something is true or not true.

Scientists are always looking for evidence when they carry out inquiries.

Can you see fur in this picture? This evidence suggests that tit is an animal, not a plant.

We know that plants don't usually have fur, but lots of animals do.

You might even have an idea of what type of animal it is, because only some types of animals have fur, and only some types of animals are that orange-y brown colour.

What other evidence would you need to collect to help you identify this living thing? Based on the evidence we have in this picture, we could assume it could be one of a few different animals.

But we can't be sure which one.

What additional evidence would you like to have to help make you more certain about what animal it is? Now we have zoomed out of the picture a little, and now we can see even more of the animal.

Now that you have some more evidence to consider, have your ideas about what the animal could be changed? You could use all of the evidence provided to suggest a theory for what you think the animal is.

Theory is another of our keywords for today.

A theory is a carefully thought out explanation about something.

Theories are always based on evidence and are never just guesses.

The animal is a cow.

Did your ideas change as you were able to gather more evidence about the animal? When I first saw the fur, I thought the animal was a dog, because I know dogs have fur.

When we got to look at a bit more of the animal, though, I knew my theory wasn't correct, because dogs don't have noses like the one in the picture we could see.

Even though it wasn't the right animal in the picture, my first theory wasn't a bad theory because it was based on all the evidence that I had.

This is how scientists make and adjust their theories about the world and everything in it over time.

They suggest a theory based on the evidence they have, look for evidence, and then change their theory if the evidence suggests something different.

For centuries, scientists have been gathering evidence and making and testing theories about our solar system.

It has been very challenging for them, because space is a very tricky thing to investigate without the right equipment.

For most of human history, we've not been able to travel into space to find the answers to our questions, and scientists have had to use the evidence they could gather from Earth.

Over time, their ideas have changed and their theories have improved as they have been able to make closer observations using technology like telescopes and satellites.

You can see a telescope in the picture there, and you might even have used a telescope yourself.

Telescopes are good for making objects that are far away look closer, so they are useful for making observations of planets that are very far away.

Satellites are pieces of equipment that are sent to orbit the Earth and make observations.

You might have heard of the Hubble Space Telescope, which is a satellite currently in orbit, gathering information and images for scientists to look at back on Earth.

We've covered a lot of information there, so let's do a quick check on our understanding so far.

What is a theory? Is it A, a guess about how something works? B, an idea that cannot be proven? C, a well-thought out explanation for something? Or D, a plan for carrying out an experiment? The correct answer is C.

A theory is a well-thought out explanation for something.

Now, for this check, You need to take a look at the children's ideas, think carefully about them, and then decide who you agree with.

Sam says, "Scientists' ideas about the solar system "are always changing as they gather more evidence." Jun says that, "Scientists have always had the same ideas "about the solar system.

"They have all the evidence they need." And you might want to pause the video here for some thinking time or to discuss the ideas with a partner and then come back when you are ready.

Did you agree with Sam? She is correct.

The scientists are always gathering more evidence and changing their ideas based on what they have discovered.

Time for you to start learning from the first part of our lesson with a practise task.

Your job is to read the theory and answer the questions below.

Here is your theory to consider, ancient Egyptians thought the sun was the God Ra who brought them good weather and healthy crops.

They thought he moved through the sky using a chariot and died each evening.

So that's our theory for you to be thinking about.

First, I'd like you to think about what evidence were the ancient Egyptians have had that supported this theory? This might be quite tricky, because we know now that the sun isn't moved by a god in a chariot.

But the ancient Egyptians had thought about this carefully and had used the evidence they had available to them to create this theory.

What evidence do you think that could have been? Then, for the second part, you need to think about what evidence we have now in modern times that disproves this theory.

There's quite a lot to think about there, so pause the video and have a good think and maybe discuss your ideas with a partner, and then come back when you are ready.

Let's take a look at the first part of the task.

What evidence would the ancient Egyptians have had that supported their theory about the sun's movement across the sky? Here are some possible ideas.

They might have thought the sun seems to move across the sky during the day and then disappear completely at night.

So to them, it looked like the sun was moving and they didn't feel like they were moving, so it was reasonable to assume the sun was actually moving.

This might even have been something you thought before you learned that the sun doesn't move around in the solar system.

Another piece of evidence the Egyptians may have had is when the sun is bright and the weather is good, our crops are more plentiful.

So they may have thought this was evidence that a god who brought the sun was the reason the crops were growing so well.

Or you may have thought, the Egyptians thought, the sun is very big, so it must need something like a chariot to move it.

Ancient Egyptians used chariots to move around, so they could have thought a chariot was the reason the sun was moving.

Did you have any of the same ideas? Or did you think of anything else? Now, onto the evidence we have now that disproves this theory.

We know now that the sun does not disappear at night.

It just cannot be seen as our part of the Earth rotates away from the sun.

Scientists have modern equipment to safely observe the sun, and we have seen that there is no chariot pulling it along.

We also know now that the sun is the centre of the solar system and it doesn't move across the sky.

We know that we are the ones that are moving, even though it doesn't feel like it.

Did you think of any other evidence that disproves the theory of the ancient Egyptians? Let's move on to the second part of our lesson today, geocentric and heliocentric models.

We have not always known as much about the solar system as we do now.

Hundreds of years ago, scientists did not have equipment like telescopes to make closer observations of objects in space and how they moved.

They had to gather evidence using their eyes alone.

This must have been incredibly tricky, especially considering that from Earth, without telescopes or binoculars to get a closer look, the other planets look very similar to stars in the night sky, just a tiny bit bigger and a tiny bit brighter.

Around the fourth century BCE, sometimes called the fourth century (birds chirping), ancient Greek philosophers Aristotle and Plato were working on a theory about the solar system.

So this was over 2020 years ago.

Long before space travel was possible.

Their theory put the earth still or stationary at the centre of the solar system, and the sun, moon and planets orbiting around it.

This theory was based on their observations of how the sun, moon, and other planets appeared to move across the sky, while it felt like Earth stayed still.

It is not surprising that they thought the earth didn't move.

Think about it.

Can you feel the earth moving now? Would you have known that it is actually moving incredibly fast through space as we speak if no one had told you? This idea about the earth being stationary, in the centre, is called the geocentric model of the solar system.

You can see in the diagram there that the Earth is in the middle and the sun, planets and moon are all orbiting around it.

The prefix geo means Earth, so geocentric means Earth at the centre.

You might have heard this geo prefix on other words like geography, which is the study of Earth.

If you can remember that geo means Earth, then that might help you to remember that geocentric means Earth at the centre.

Let's do another check for understanding.

What is at the centre of the solar system according to the geocentric model? Is it A, Earth? B, the sun? Or C, the moon? Great.

The Earth is at the centre of the solar system according to the geocentric model.

Next question.

How did ancient philosophers develop theories about space? Do you think, A, they read books about space? B, they observed how objects in space moved in the night sky? Or C, they watched television programmes about space? Well done if you thought the answer was B.

They observed how objects in space moved in the night sky.

For many years, all the scientists continued making observations of the movement of objects in space to see if they agreed with this theory.

Sometimes their evidence agreed with the geocentric model.

Sometimes it didn't.

In the picture here, you can see an astronomer from the 15th century called Ulugh Beg.

He built a cutting edge observatory in what is now Uzbekistan that housed a range of the most modern equipment for observing space at the time.

He and other astronomers used this to gather evidence and debated whether it supported or disagreed with the geocentric theory.

And around 1500 CE, also known as 1500 AD, a number of scientists across the world were working on a very different theory about the solar system.

In 1543, after many years of collecting evidence from his own observations of the night sky, Polish astronomer Nicolaus Copernicus published his theory of the heliocentric solar system.

Other scientists had been having similar ideas around the same time, but Copernicus was the first to formally publish his ideas and share them with the world.

The heliocentric model of the solar system has the sun at the centre and the eight planets orbiting around it.

You can see what this looks like in the diagram here.

This'll probably look familiar to you because it is the scientifically accepted model of the solar system now.

Time for another quick check to see how we're doing.

What does heliocentric mean? Does it mean A, the earth is at the centre? B, the moon is at the centre? Or C, the sun is at the centre? Fantastic.

It means C, the sun is at the centre.

Now, Copernicus was met with A a lot of resistance from others who thought his theory was wrong.

As you can imagine, it would've been quite hard for people who have believed one thing all their life to suddenly change their thinking.

After he died, other scientists continued his work including an Italian astronomer called Galileo Galilei.

Galileo developed a telescope in 1609 to make better observations of the solar system, and found that his evidence supported the heliocentric theory published by Copernicus.

Galileo's heliocentric model was also met with resistance from the Roman Catholic Church, who at the time firmly believed that the Earth was the centre of the solar system.

In this time period, the Roman Catholic Church was very powerful and it was a very risky thing to challenge them in the way that Galileo did.

In 1663, he was ordered to stop promoting the heliocentric model by the church, and he was sentenced to life in prison.

Luckily for him, he was allowed to carry out his sentence as house arrest, meaning he was confined to his home rather than a prison cell.

Despite his punishment, Galileo carried on working on his heliocentric model from home.

He was not scared into submission.

Since then, scientists have continued learning more about our solar system thanks to developments in technologies such as improved telescopes, space, travel, and satellites.

All of our recent observations have provided further evidence that this theory of the heliocentric model is correct.

It really is amazing that scientists from across the world and across history have all helped in gathering evidence to help us come to this understanding now.

That was a lot of information for you to take in there, so let's do a quick check to see how things are going.

Who was the first scientist to publish a theory about the heliocentric model of the solar system? Was it A, Isaac Newton? B, Nicolaus Copernicus? Or C, Aristotle? It was B, Nicolaus Copernicus was the first scientist to publish a theory about the heliocentric model.

Let's have a go at another practise task now.

Carry out some research to find out more about Galileo, his discoveries and how he was treated for making his theories public.

You could find out what evidence he saw that supported the heliocentric model and how he was punished for sharing his ideas.

Then write a short diary entry from the viewpoint of Galileo explaining why he agreed with the heliocentric model theory and how he felt about his treatment for sharing his ideas.

Remember, when people write in a diary, they talk about their thoughts and feelings.

As I'm sure you can imagine, Galileo probably had quite a lot of thoughts and feelings about the unfair treatment he got just for trying to share his evidence with the world.

Try to put yourself in his shoes when you are writing your diary entry, and really think about what he might have said.

Pause the video here and have a go at these tasks.

Come back when you're done.

How did you do? Did you enjoy being creative with your diary entry? Did it help you to understand what it must have been like for Galileo? Here is some information I found carrying out my research.

Maybe you found some of these things too.

Galileo studied both medicine and mathematics at university.

He learned about the invention of the telescope in the Netherlands in 1609, and developed his own version that could see even further.

He made observations that agreed with Copernicus' theory and published a book about it in 1632.

He was then sentenced to life in prison in 1633, but he was allowed to live in his home in Tuscany under house arrest.

He continued studying and writing from his home until his death in 1642.

And here is my diary entry.

I cannot believe I'm stuck here.

For years, I have worked on Copernicus' theory of a heliocentric solar system, and my evidence has convinced me that he was right.

With my powerful telescope, I've been able to make observations of the movement of the heavenly bodies, and I'm now certain the sun is at the centre of the solar system and all the planets travel around it.

In particular, my observations of the phases of Venus make it clear that it orbits the sun, not Earth.

Yet here I am confined to my home by the Roman Catholic Church because they refuse to believe the theory, despite all of the evidence.

Hopefully one day there will be too much evidence to deny and they will see that I am right.

I'm sure your Galileo diary entries were wonderful and creative.

It might be a good idea to share yours with a partner.

We've come to the end of our lesson.

Let's recap our key learning for today.

Theories about the solar system have developed over time.

For many years, people believed in the geocentric model of the solar system.

Now, we know that the sun is at the centre of the solar system and planets all orbit around it.

This is called the heliocentric model.

Thank you for joining me for this lesson today,, and thank you for your careful research work and creative diary writing.

I've really enjoyed learning all about scientific theories and scientists from the past with you.

See you again next time.