Lesson video

Hello and welcome to today's lesson from the unit, "Earth, Sun, and Moon.

" This lesson is called, "Why We Have Day and Night.

" Hi, I'm Mrs. Waller, and by the end of the lesson today, you will be able to explain why we have day and night.

Let's take a look at the keywords we'll be using in the lesson today.

Earth, Sun, rotate, axis, and model.

Take a moment to think about these words.

Do you already know what any of these words mean?

Maybe you could explain your thinking to a partner.

Today's lesson is in two parts, and in the first part of the lesson, we'll be learning about a spinning Earth, and then we'll be moving on to the second part to think about day and night, in particular, why we have day and night.

We live on planet Earth.

The Earth is the shape of a sphere.

People often talk about an imaginary line that goes through the center of the Earth from the North Pole to the South Pole.

Do you know what this imaginary line is called?

It's called its axis.

Now, the axis is a very important line because the Earth actually spins.

It spins around on its axis, so the Earth spins round on its axis, just like a ball spinning.

The Earth spins in an anti-clockwise direction.

When scientists are describing how the Earth spins on its axis, they often use the word rotate.

When the Earth rotates on its axis, it doesn't suddenly speed up and slow down.

It's rotating at a constant speed, and this speed is around 1,000 miles per hour.

So you might think that the Earth is rotating at a really high speed.

So how long does it take the Earth to rotate just once on its axis?

Well, you might think it doesn't take very long at all for the Earth to rotate at that speed, but actually because of its really large size, it takes the Earth 24 hours to complete one full rotation.

It's time for me to check your understanding of the spinning Earth.

So our first question is what is the name of the imaginary line that goes straight through the center of the Earth?

Is it the axis, the North Pole, or the Equator?

Yes, well done.

It's the axis.

And don't forget it's not a real line, but it's an imaginary line that goes from the top to the bottom of the Earth, from the North Pole to the South Pole.

True or false, the Earth moves on its axis like a spinning basketball.

Do you think that's true or false?

Yes, that's true.

Do you think you could justify your answer?

Could you explain why you think this is true?

That's right, the Earth spins or rotates on its axis, and this movement looks like a basketball spinning on somebody's finger.

So yes, the Earth does move on its axis like a spinning basketball.

Now, how long does it take the Earth to rotate once on its axis?

Is it 24 minutes, 24 hours, or 24 days?

And the answer is B.

It takes the Earth 24 hours to rotate once on its axis.

Well done.

Now, moving on to your first practice task.

I would like you to make a simple model to demonstrate this happening, so I'd like you to think of what you might need, what could you use to represent the Earth?

And how could you represent the axis?

And I want you to choose some objects and I want you to demonstrate the Earth rotating on its axis.

So pause the video, have a think about it, gather some objects, and I want you to model the Earth rotating on its axis.

Off you go.

Once you've made your model, can you use your model to explain to somebody else how many times the Earth rotates on its axis in one day?

So here's some ideas for you.

"I chose a football and spun it round using my finger on the tabletop so it looked like the Earth spinning on its axis.

" Well, that's a good idea, isn't it?

A bit like the basketball spinning on the finger, but we've got the finger on the top of the ball on the tabletop, and we're spinning the ball, and we're using our finger to represent the axis.

Here's another idea.

"I rolled dough into a ball and I pushed a stick through it for the axis so I could rotate it easily.

" Oh, I like that one, don't you?

So you could take some dough, and you could mold it into a sphere shape to represent the Earth, and then using some kind of a stick or a pencil, you can push it right through to show that imaginary line going from the top to the bottom of the Earth, and you could hold the stick in your hand, and maybe you could spin it, you could rotate it 'round to represent the Earth spinning on its axis.

Did you have any different ideas?

Now, don't forget the second part to this task.

Use your model, and while you are rotating your Earth on your axis, can you explain to someone how many times the Earth rotates on its axis in one day?

We write, yes, so we know that it takes the Earth 24 hours to rotate once on its axis.

So that means that the Earth must rotate once on its axis in one day, because there's 24 hours in one day.

Did you get that one correct?

Fantastic.

We're moving on to the second part of this lesson now, and once we know about the spinning Earth, the fact that the Earth rotates on its axis, then we're going to use this idea to explain, why do we have day and night?

The Sun is very important to us.

We know that it's the center of our solar system, and one of the things that the Sun gives us is light.

Now, the Sun gives us light here on Earth during the day, but it's dark at night.

So have you really given that some thought, if we look at the photograph of the daytime, where it's nice and light, but then think about what happens at night, when it becomes dark.

Why do you think it gets dark at night?

Take some time to give this some real thought and explain your ideas to someone else.

Now, we've been learning in the first part of this lesson about the spinning Earth.

We now know that the Earth rotates on an imaginary line called an axis, and actually it's this that causes day and night.

Let's think about this some more.

As the Earth rotates on its axis, the part where you live will spin around to face towards the Sun, and then as it continues to rotate, it will keep spinning to face away from the Sun.

Take a look at this scientific diagram here so we can see the spherical Earth, and the imaginary line going straight through the center of the Earth, and I want you to imagine that the Earth is slowly rotating.

So we can see that circular arrow going around the Earth, showing us that it's rotating in an anti-clockwise direction.

Now, if you can imagine that as you are spinning towards the Sun, and then you are spinning away from the Sun, this is what is happening when it's getting lighter and then when it's getting darker on Earth.

As I've said already, the Sun is the center of our solar system, and it gives all living things warmth and light.

So if we have a look at our Sun at the side of the slide deck, and we have our yellow arrows representing some of the light that comes from the Sun.

Now, as we think about the spinning Earth, as the Earth rotates on its axis, the part of the Earth that's facing the Sun has daytime.

Take a look at the image on the screen and that really helps us to understand what's happening.

We can see a full half of the Earth that's being lit by the Sun, and if that was the part of the Earth where you are, then it would be daytime for you.

Let's keep thinking about this.

The part of the Earth that's facing away from the Sun is in darkness.

It's not being lit by the Sun at all, is it?

It's facing away from the Sun.

So if we were there at this moment in time, we would have nighttime.

Let's use this idea to think about how people living in different parts of the world experience day and night at different times.

So I'm going to show you a video clip now, and I want you to look really carefully, and we can notice the light from the Sun is shining on one side of the Earth, and if we can maybe choose a country on the Earth, if you can look really carefully and fix your eyesight on one particular part of the Earth as it's rotating 'round to face the Sun, then that part of the Earth would be experiencing daytime.

So let's summarize that, "As your part of the Earth rotates towards the Sun, it gradually becomes lighter.

And when you are directly facing the Sun, it's midday.

" So let's keep thinking about this.

As your part of the Earth rotates away from the Sun, it's gradually becoming darker.

And when you are facing directly away from the Sun, then it's not midday, it's midnight.

Let's take another look at the video clip.

So if we can imagine that we're there on one little part of the Earth, if you can find a particular country, and think that's you there in your part of the world, and we can see that the Earth is rotating towards the light of the Sun, and then I want you to imagine that you are continuing that rotation.

And as your part of the Earth is gradually facing away from the Sun, it's getting darker and darker until your part of the Earth is facing away from the Sun completely, and that's when it would be midnight.

So what's happening as you continue the rotation even further is it's gradually getting lighter again until it's daytime.

So just to check your understanding of this, when it is midnight for us, what time is it for somebody living on the opposite side of the world?

Yes, if it's midnight for us, then it's going to be midday for them.

Well done.

Understanding things that we can't experience for ourselves, such as what happens in space, and why do we have day and night, can be really tricky.

So quite often people use models, a bit like the model that you've already used in your first task.

So you modeled the Earth and its axis, and you modeled how the Earth rotates on its axis.

So let's look at another type of model.

Now, this one looks a little bit more complicated, doesn't it?

It's called an orrery.

And if you look really closely, it's a series of rotating discs, and we have a model of the Sun in the center, and you might be able to work out we have two more spheres, one of them is the Earth, and the smaller one is the moon.

Now, the orrery is a model, and it spins to show how things move in space.

Different parts of an orrery can be used to explain, why do we have day and night?

So maybe that disc there that's got the Earth attached to it will rotate 'round, and we can think about which part of the Earth is facing towards the Sun, and which part of the Earth is facing away from the Sun.

It's time for me to check your understanding about why do we have day and night.

True or false, it is nighttime when your part of the Earth is facing the moon?

Do you think that's true or false?

Yes, it's actually false.

It's tricky on that one, isn't it?

So let's think about the spinning Earth.

Can you justify your answer?

It is nighttime when your part of the Earth is facing the moon.

Now, we know that that is false.

So can you explain why?

It's false because it's not that the Earth is facing the moon, it's that the Earth is facing away from the Sun when it's night.

How about this one, "What movement in space causes day and night?

" Is it the Sun that rotates on its axis, the Earth that rotates on its axis, the Sun moves around the Earth, or the Earth moves around the Sun?

Think really carefully about this one.

Yes, well done, It's B.

We know that the Earth rotates on its axis, and when the part where you are is facing towards the Sun, it's daytime, and when your part rotates and faces away from the Sun, it's nighttime.

"The Earth rotates in an anti-clockwise direction.

What will be happening at the cross on the Earth below in the next few hours?

" So look really carefully at the light that's coming from the Sun, and we've got one half of the Earth in daylight, and the other half of the Earth experiencing nighttime.

So if you lived where the cross is on the image of the Earth, what do you think would be happening in the next few hours?

Would it be getting lighter, would it be getting darker, or would it be staying the same?

Yes, that's right.

It would be getting darker, because the Earth rotates in an anti-clockwise direction, so if you were where the red cross is on the Earth, you would be continuing to rotate away from the light of the Sun.

Time for your next set of practice tasks.

And we're going to continue to think about how we can use models to help us to demonstrate why we have day and night.

So again, I'd like you to choose an object to represent the Earth, and you could use a bright torch, or maybe the torch from your phone or a tablet, to represent the Sun.

And I want you to use these objects to demonstrate why we have day and night.

Now, it'd be fantastic if you could actually video your moving model.

Pause the video and think about what you could use.

Once you've made your video, I'd like you to write a short commentary to explain why we have day and night to accompany your video.

So you can play video, and you can have you explaining the whole process, Speaking over the top.

You'll need to think really carefully about which science words you will include.

Let's take a look at some ideas.

I think it would be something like this.

"The Earth rotates on its axis in an anti-clockwise direction.

" "When the Earth rotates away from the Sun, it becomes darker.

When we are facing away from the Sun, it is night.

" "When the Earth rotates towards the Sun, it is getting lighter.

When we are facing the Sun, it is day.

" Pause the video again and take some time to go back to your commentary.

Would you like to improve it in any way?

Have you used a different kind of explanation to accompany your video?

It would be brilliant if you could compare your explanation with someone else's.

Let's keep thinking about this.

Sam makes a model of the Earth and the Sun.

He uses a ball on a stick for the Earth.

He uses a ring light for the Sun.

What should Sam do to show why we have day and night?

Should Sam walk with the ball around the light?

Should Sam spin the ball on the stick?

Should Sam swing the ball backwards and forwards?

Or should Sam hold the ball higher and then lower?

Which one do you think?

Can you also explain why you think this?

Let's take a look at the answer.

"Sam should spin the ball on the stick," is that what you said?

Yes, because the ball represents the Earth, and the stick represents the axis, and the Earth rotates on its axis.

Let's have a look at a more detailed explanation.

"This would show the Earth rotating on its axis," Yes, that's just what I said.

"The part of the ball facing the light will show that part of the Earth in daytime.

The part of the ball facing away from the light will show that part of the Earth in nighttime.

As Sam spins the ball, different parts of it will be lit by the Sun in 24 hours.

" Take some time to compare your reasons why with the one on the screen here.

For this task, I'd like you to think back to an orrery, which is a model of the Earth's Sun and moon.

There's the Sun, there's the Earth, and there's the moon.

And an orrery is a really clever way of connecting these three things together.

And one of the things that we can show with an orrery is, why do we have day and night?

If you were to think about it, on this diagram, which part of the Earth would you shade in, maybe with a dark pencil, to show where it is nighttime on Earth?

And can you also explain why do you think this?

Is this what you thought?

Have a look on the diagram.

"I have shaded nighttime on the Earth, and I think this is right because this part of the Earth is not facing the Sun.

" So if we look at the Sun, and if we look at the part of the Earth that's directly in the Sun's light, we're going to shade in the other side of the Earth that is facing away from the Sun, because it will be dark there.

Is this the same as what you thought?

We're coming towards the end of the lesson now.

Let's summarize our learning today.

"The Earth's axis is the imaginary line that runs from the North Pole, through its center, to the South Pole.

" What else can you remember from the lesson today?

It might be that the Earth spins or rotates on its axis, and this takes 24 hours.

So the Earth rotates once every 24 hours, well done.

And finally, "As the Earth rotates on its axis, the part of the Earth facing the Sun has daytime, and the part facing away from the Sun has nighttime.

" Well done, there's a lot of scientific information in the lesson today, and I'm sure that you can understand this really well now, and you could go and explain this to someone else.