Lesson video

Hello and welcome to this lesson on earth's tilt.

This is from the unit called Our Solar System and Beyond.

My name's Mr. Norris.

So in this lesson, we're gonna look at how the spinning earth is not actually spinning kind of straight up, but is spinning on a tilted axis, and this leads into a understanding of the seasons.

So if we want to understand how the seasons change, actually it's really complicated.

We need to understand heating by the sun first, and in this lesson, we're gonna look at how that causes it to be different seasons at the same time of year in different places on earth.

There's a future lesson where we'll look then in more detail at how seasons actually change from one to the other.

So let's get on with this lesson, which introduces earth's tilt and how it can be different seasons on earth at the same time in different places.

Off we go.

The outcome of this lesson is that, by the end of the lesson, you'll be able to explain why it's winter in the southern hemisphere at the same time as when it's summer in the northern hemisphere on earth.

Here are some key words that will come up this lesson.

Summer, winter, hemisphere, axis and tilt.

Each word will be explained as it comes up in the lesson.

This lesson is divided into three sections.

In the first section, we'll just recap the key differences between summer and winter in the UK.

In the second section of the lesson, we'll look at the seasons in the UK and also in another area on earth's surface that I've carefully chosen, which is southern Chile.

And in the third section, we will then look at how we can use earth's tilted axis to explain the seasons in the UK and southern Chile and in other places on earth too.

So let's get going with the first section.

So in the UK, there is a yearly cycle of seasons, which I'm sure you'll be familiar with.

Spring becomes summer, which becomes autumn, which becomes winter.

And then after winter, you get a new spring, which is always a lovely time of year as the weather starts to be a bit warmer, the day starts to get a bit longer and kind of spring flowers like daffodils come up from the ground.

And it's important to remember that the seasons change gradually.

There's not a definite cutoff point between each season.

And in fact, depending on how you are looking at the seasons, whether you are looking at weather patterns or whether you are looking at earth's orbit around the sun over one year, you can define the start and end of each season differently.

And the same pattern repeats every year in the same months pretty much.

So let's just check that you know, in which months does each season happen in the UK? So look at the list of months and you've got the four seasons of four boxes, box one, box two, box three, box four.

Which season occurs in which months in the UK? Pause the video now and make sure you can fill in the four seasons into the four boxes.

Off you go.

Okay, some quick feedback on that.

So spring goes in box one because that is the season which tends to occur from kind of perhaps late February sometimes to mid-May.

And then, by late May and June, July and August, they're the warmest months of the year with the most number of hours of daylight each day.

So that's summer.

And then by the end of August and going into September, the trees are starting to change colour to the autumn leaf colours and it's starting to get a bit colder again.

And then by late November and December, it definitely feels colder like winter.

So that is when the seasons happen in the UK.

So let's talk now about the three main differences between summer and winter.

And I'm gonna illustrate these with pictures and examples from the UK.

But the ideas about these three main differences between summer and winter, they actually apply to all countries that have a summer and a winter.

Even if they're summer is different to our summer, it might be hotter or it might be colder, but it's still that country's warmest season.

And the same for other countries' winters.

Other countries' winters might be colder or might be different to the UK's winter, but it's always that country's coldest season.

So it's always true that temperatures are higher in summer on average than in winter.

The second key difference is that there are more hours of daylight in the summer season than in the winter season.

For example, in the UK, in the middle of June when it's summer, sunrise might be at 5:00 AM and sunset might not be till nine in the evening.

That gives 16 hours of daylight in the 24-hour day.

The time taken for the earth to spin once on its axis, which is one day, is always 24 hours and 16 of those are in daylight in the UK in June when it's summer.

But in December, the sun might not rise till eight in the morning and the sun might set as early as 4:00 PM.

That only gives eight hours of daylight in the UK in December when it's winter.

So 8:00 PM in June can still be lovely and sunny and warm and you can be sat outside enjoying a nice summer's evening, but you can't do that in the same way in December because by 4:00 PM the sun will have set and it will be dark and cooler in the UK in winter.

Let's do a quick check on what we've just said.

So look at the two students' ideas.

Laura says, "A day always lasts 24 hours on earth." Alex says, "A day in winter is shorter than a day in summer." So whose idea is correct and whose idea could be more clearly worded? Work out which student has the correct idea and which student's idea could be more clearly worded.

Five seconds to decide.

I'll give you some feedback on this now.

Well done if you identified that Laura is absolutely correct.

And Alex, I kind of know what Alex is getting at, but actually it could be clearer because both of these students' ideas can't both be true at the same time.

Because if a day is always 24 hours on earth, then how can a day in winter be shorter than a day in summer if it's always 24 hours? So Laura is definitely right.

I know what Alex is getting at, but I think he can make it a bit more clear.

Can you make it a bit more clear? Can you improve the wording of Alex's idea by completing the sentence? Put the right word in the gap to explain what Alex really means.

Pause the video now and have a go at doing that.

Well done if you worked out that what Alex is really talking about is the number of hours of daylight.

In winter, each day has fewer hours of daylight.

A day is still 24 hours, but fewer of them have daylight than in summer.

In summer, there are more hours of daylight, but a day is still 24 hours.

So sometimes people say, in summer, the days are longer, and technically that's not quite true.

The day is still 24 hours.

What people mean when they say the days are longer in summer or the days are shorter in winter is the number of hours of daylight is different, but a day is still always 24 hours.

So that's the time taken for the earth to spin once on its axis.

Here's the third key difference between summer and winter in the UK.

The curved path of the sun across the sky is higher in summer than in winter.

So this shows the curved path of the sun across the sky as seen from the UK in summer.

You can see sunrise is towards the east and then the sun moves westwards or appears to move westwards across the sky.

And remember, that's because actually it's us that's turning.

Earth is spinning and that causes the sun to appear to move westwards across the sky when in fact it's us turning anti-clockwise on a spinning earth.

And then, the sun sets in the west.

However, this is the path of the sun across the sky in winter.

It's much lower.

So it still rises in the east and move westwards and the sun still sets in the west, but the sun's path across the sky is much lower in winter than in summer.

Okay, let's do a check on everything we've gone through about summer and winter.

Complete the three main differences between summer and winter.

For this one, I think you should pause the video and work out what goes in each gap for the three main differences between summer and winter, especially in the UK.

Off you go.

Right, I'm gonna give some feedback now.

So make sure you've completed all three.

So the first key difference, something is higher.

The best one to fit in there is temperatures are higher in summer than in winter.

You could I suppose have put about the sun is higher in the sky, but that fits better in number three.

Number two, there are more hours of daylight or daylight hours during summer days than during winter days.

That's the best one that fits in there.

And then for number three, the curve path of the sun across the sky is higher in summer than in winter.

So that was the best way of describing the three differences into those gaps.

Well done if you got those in the right places.

Right, time for a quick task now.

You need to summarise everything we've just gone through.

So a bit like the check for understanding we just did, but sorting it all out for summer and winter.

So the first part of this task is to add summer and winter as headings into the correct columns.

Okay, so the first column says in the UK, but the second column's heading is blank.

Should that be summer or winter in the UK? Look at the months.

And the third columns heading is blank from late May to August.

Should that be summer or winter? So we're only worrying about summer or winter at the moment.

There's nothing about spring or autumn in this task, just summer and winter.

Once you've put the correct headings in the correct columns, then you can complete the rest of the table to summarise the main differences between summer and winter.

You don't need to give numbers, you just can give descriptions about average temperature.

Hours of daylight could be more or fewer hours of daylight and height of the sun could just be higher or lower depending on which column you're filling in, the summer column or the winter column.

So pause the video now and have a go at completing that task with your best effort.

Okay, off you go.

Right, well done for completing that task.

Here's some feedback.

So the first column was winter because that's the season in the UK between late November and early February.

And the second column should have been labelled summer because that's the season from late May to August in the UK.

And then, the average temperatures, hours of daylight and height of the sun are filled in in this table for you.

So pause the video now and check that yours matches what's on the screen.

Well done for your effort on doing that.

Time for the second section of the lesson now.

And in this section, we're gonna compare the seasons in the UK that we just looked at to the seasons in a place I've carefully chosen on earth, southern Chile.

So what we should say first is that places on earth that are a similar distance from the equator, which is that line there, can have similar climates and seasons if there a similar distance from the equator.

So it's useful to be able to talk about the northern hemisphere, so that's everything above the equator and look on the globe as well 'cause remember the earth's got a tilt.

We've mentioned that already, but we'll go into more detail later in the lesson.

So anything that's above the equator we say is in the northern half of the earth or the northern hemisphere.

And anything that's below the equator we say is in the southern hemisphere, is south of the equator.

And we should know or hopefully you'll be aware of already, that the heating effect of the sun's rays is greatest closer to the equator.

And that's because near the equator, earth's surface is closer to being face-on to the sun.

And that means the sun's rays arrive at close to 90 degrees to earth surface.

So that means they're less spread out over the ground when they hit the ground.

That leads to a greater heating effect at the equator.

But what about near the poles or further from the equator? There, earth's surface is further from being face-on to the sun.

If you look in that diagram, the equator is kind of face-on to the sun's rays.

And if you go up towards the north pole, you're less and less and less face-on to the sun's rays because of the curve of the earth.

And that means the sun's rays arrive from a much lower angle, so they're more spread out over the ground.

So there's less of a heating effect further from the equator, near earth's poles.

Let's do a quick check on what we've just said.

Why do places near the equator have hotter climates? Can you fill in the gaps? Pause the video now to see if you can do that.

I'm gonna give some feedback now.

Places near the equator are closer to being face-on to the sun and that means the sun's rays are less spread out across the ground near the equator, causing a greater heating effect near the equator.

Well done if you got that right.

Let's do another quick check now of what we just said.

Which locations, so letters, A, B, C, D, E and F, which of those places could have a similar climate and seasons to the UK? So remember what we just said about what can make something have similar climate and seasons to the UK and work out which of those places that applies to to give them similar climate and seasons to the UK.

Pause the video now and have a go.

I'll go through some feedback now.

Well done if you remembered that places that are a similar distance from the equator will have or can have similar climates and seasons.

So what we're looking for is locations that are a similar distance from the equator to the UK.

So A is a similar distance from the equator to the UK.

So location A could have similar climate and seasons to the UK, but B is too far north.

C could have similar climate and seasons to the UK 'cause it's a similar distance to the equator.

Places D and E are probably gonna be warmer than the UK because they're closer to the equator than the UK is.

But place F, that is a similar distance to the equator as the UK is.

It doesn't matter that it's in the southern hemisphere because the curvature of the earth will be similar to the UK if it's a similar distance to the equator as the UK is.

So well done, if you've got A, C and F could all have a similar climate and seasons to the UK because they all are a similar distance to the equator as the UK is.

So place F from that check for understanding was the most southern part of a country called Chile in South America.

And we've said that they have similar seasons because they're the same distance from the equator, it's just the UK is north of the equator and Chile is south of the equator.

So the UK is in the northern hemisphere and Chile is in the southern hemisphere.

And what that means is, although their seasons are similar, they don't occur at the same time of year for both places because they're in different hemispheres.

Let's look at why that is.

So in June, in the UK, it's summer.

Average temperatures are warmer, there's around 16 hours of daylight every day in June in the UK and the sun is high in the sky in June in the UK.

Whereas at the same time, which is still June, in southern Chile, it's winter.

So at that exact same time, June, that time of year in the UK, it's summer, but in southern Chile, it's winter.

That means average temperatures are colder, there's only around eight hours of daylight each day and the sun is low in the sky, much lower than in the UK at the same time 'cause it's summer in the UK and it's winter in southern Chile in June.

Let's do a quick check that you've got the idea of when the seasons happen in southern Chile compared to in the UK.

So there are four boxes, one, two, three and four.

Put the correct season in the correct box to show the months when each season happens in southern Chile.

And you've got when each season happens in the UK as a reminder on the left, but all you need to fill in is boxes one, two, three, four, when does each season happen in Southern Chile? Let's check that we've got what we've just been talking about.

It might help to start with June 'cause that's what we were just talking about and everything else should go from there.

Pause video now, make sure you can do that.

I'll go through the answers to this check now.

Okay, so I suggested starting with June 'cause that's what we were just talking about.

We said that in June in the UK, it's summer, but in southern Chile, it's winter.

And then, after winter always comes spring.

So that goes in box three.

Then after spring always comes summer.

And we've said that southern Chile has its summer in December, which is when the UK is having its winter.

The coldest season in the UK is in December, but that's when southern Chile has its warmest season, summer.

And that leaves autumn to go in box one.

So well done if you got all of those.

The key idea here is that, places in the northern and southern hemispheres have their summers and winters at opposite times.

And in the last learning cycle of the lesson, we're gonna look at why that is.

But before we do that, let's just summarise, make absolutely sure that we've got this idea right, that the seasons are happening in different places in June in the UK and in southern Chile as an example of a southern hemisphere country.

So it's another table to fill in and this one's slightly different.

So it's not the same as the one from task A.

In this one, I've given you June in the UK and June in southern Chile.

And you've got to fill in what season is it in June in the UK and what season is it in June in southern Chile.

And then, also fill in what are the temperatures like, what are the hours of daylight? What's the height of the sun like in June in the UK and in June in southern Chile when it's the different seasons that we've talked about? So pause the video now and have a go at filling in that table.

Off you go.

Okay, here's some feedback.

So the most important boxes were, what season is it in June in the UK? It's summer.

And then, you can see the rest of what it's like in summer, warmer, lots of hours of daylight, the sun's higher in the sky.

Whereas in June in southern Chile, it is winter.

So it's colder, there's fewer hours of daylight and the sun is lower in the sky.

So make any corrections you need to on your table, and well done for your effort on that task.

Right, so we're now onto the final section of the lesson where we're going to look at the idea of earth's tilted axis and how that explains the different seasons in different places at the same time on earth.

So the axis of a spinning object is an imaginary line that we can imagine drawing because that's the line around which a spinning object is spinning.

So the blue dash line there is the axis of that toy which is spinning, and the axis in that picture is vertical.

The toy is spinning around vertical axis.

But you could make that toy spin anywhere around you like, okay? You could hold the toy in that direction, so the axis of rotation is now horizontal.

The toy is vertical, but the axis of rotation, the imaginary line around which the toy's spinning, that's now horizontal.

So the axis is the imaginary line around which something is spinning.

And of course, earth is spinning, but the axis of earth spin is not vertical as you might imagine, okay? It's actually slightly tilted by an angle of 23 and a half degrees.

So that is the angle from the vertical around which earth actually spins.

Earth has a tilted axis of rotation.

So this explains the seasons, different seasons in different parts of earth at the same time because in June, it turns out the northern hemisphere or earth is in a position where its northern hemisphere is tilted more towards the sun than the southern hemisphere is.

In fact, you could say the southern hemisphere is tilted away from the sun.

And this is gonna be able to explain how in June, it can be summer in the northern hemisphere at the same time as being winter in the southern hemisphere, even at places that are the same distance north and south of the equator.

So you might expect them to have the same curvature of earth and therefore the sun's ray to have the same heating effect at those places which are equal distances north and south of the equator.

Whereas in fact the sun's rays have different heating effects at the same time of year and that's because of earth's tilt.

So actually, one side of earth is tilted more towards the sun, more face-on to the sun than, say, the southern hemisphere is.

So let's look at that in more detail in just a moment.

Let's do a quick check first though.

How does the picture show why it's winter in the southern hemisphere in June? So look at the picture, that shows the position of the earth in June relative to the rays coming from the sun, which gives the correct reason why it's winter in the southern hemisphere in June.

Is it the picture shows the southern hemisphere is further from the sun, is that's why it's winter? Is that why it's winter? Is it B, the southern hemisphere is in darkness facing away from the sun in June, that's why it's winter in the southern hemisphere in June? Or is it C, the southern hemisphere is tilted away from the sun at this time? Make your decision now, five seconds.

I'll give you the answer now, it is C.

The reason why it's winter in the southern hemisphere in June is because in June, the southern hemisphere is tilted away from the sun and it's the fact it's tilted away from the sun that explains the cooler temperatures and fewer hours of daylight and lower position of the sun in the sky.

In A, it is true that the southern hemisphere is slightly further from the sun than the northern hemisphere is at this time.

But although that is true, that is not what explains lower temperatures, fewer hours of daylight and lower position of sun in the sky.

So although A is true in June, just by a very tiny amount, it's not the reason that explains why it's winter in the southern hemisphere in June.

And B is wrong because the earth is spinning.

So although in this picture, yes, southern Chile in the southern hemisphere is in darkness, in a few hours time, it'll be in light again and it will be in the southern hemisphere and it's in winter because it's tilted away from the earth, which is C.

So that's why C is the correct reason and A and B are incorrect.

Well done if you got that.

So in June, the northern hemisphere is tilted towards the sun and the southern hemisphere is tilted away from the sun, and that explains day length.

So in pink has just come up the UK's path as earth spins.

So as earth spins, the UK follows that pink circle as earth spins on its tilted axis.

And you can see that far more hours are spent in daylight than in darkness for the UK at this time.

That's why it's summer.

So it's the tilt that explains day length.

That pink path is the path that southern Chile takes as earth spins.

And you can see at this time, because of earth's tilt, far fewer hours are spent in daylight.

So it's winter in southern Chile at this time.

So it's earth's tilt that explains this key feature of summer and winter, which is the number of daylight hours.

And also because of earth's tilt, at midday in the UK, the sun is higher in the sky.

So there's Alex in the UK, there he is in the UK, and he's looking along the earth's surface.

And if you wanted to look up towards the sun, which you shouldn't do, don't look directly at the sun, but you can see he's got to tilt his head quite high up through quite a high angle to look directly at the sun.

So the sun appears higher in the sky.

And what that means is the sun's rays have a greater heating effect because they're not very spread out over our ground when the sun is higher in the sky.

So the UK is been heated from closer to directly overhead.

So the sun's rays are gonna have a greater heating effect for that reason, and also because there's more hours of daylight.

So there's more hours of heating.

So that's the key reason why it's summer in the UK, it's because of earth's tilt and earth is tilted towards the sun at this time, making the sun higher in the sky.

So the sun's rays have a greater heating effect at this time.

Whereas in southern Chile, at midday in southern Chile, the sun is much lower in the sky.

So if Alex was in southern Chile instead looking along earth's surface, he wouldn't have tilt his head up very far at all to see the sun, and that's shown in that diagram.

So the sun ends up appearing much lower in the sky in June in southern Chile.

That's why it's winter when the sun's lower in the sky.

And a consequence of that is the sun's rays have less of a heating effect because when the sun's rays hit southern Chile, they're gonna be much more spread out over the ground because southern Chile's being heated from that lower angle, and also because there's fewer hours of daylight at this time.

So both of those factors combine to make the temperatures in southern Chile lower, so it's winter at that time in June in southern Chile and in other southern hemisphere countries too.

So that's how Earth's tilted axis explains all the features of summer and winter in countries in the northern hemisphere and in the southern hemisphere.

It's all because of earth's tilt.

Let's do a check on that.

True or false.

In this diagram, it is summer in the UK and winter in southern Chile.

So take your time to have a good look at the diagram.

Does that show summer in the UK and winter in southern Chile or is the statement false? Five seconds to decide.

Well done if you said true.

That statement is true, but justify your answer.

What's the reason that statement is true? Is it summer in the UK because the UK is slightly closer to the sun or is it summer in the UK because the UK is tilted towards the sun? Five seconds to decide.

Hopefully, that was fairly straightforward.

It was B because of what we just said.

It's summer in the UK in this diagram, which is showing June, because the UK is tilted towards the sun at this time, because of earth's tilt.

Let's do a final task for today's lesson.

This task has two parts though.

So for the first task, it's just a gap fill, but only using the words more and less to fill the gaps to explain why it's summer in the northern hemisphere in June, but winter in the southern hemisphere in June.

So here's the text with four gaps to fill with only the words more and less in the right places.

So pause the video and have a go at doing that now.

Off you go.

Well done for your effort on that task.

Let's see how you got on.

So in June, Earth's northern hemisphere's tilted towards the sun.

This is why countries in the north have more hours of daylight than countries in the south in June.

And in the middle of the day, the sun has more height in the sky and the sun's rays are less spread out on the ground.

So there's more of a heating effect when it's summer in June in the northern hemisphere.

Whereas in June, Earth's southern hemisphere is tilted away from the sun.

This is why countries in the south experience less heating from the sun in June than the countries in the north and it's winter.

Well done if you've got those four correct.

Okay, here's the second part of the task now.

In June, it is summer in the UK.

Two pupils are discussing what season it would be in Japan and New Zealand.

So have a look at the map and decide for yourself, what season do you think it would be in Japan and New Zealand in June when it's summer in the UK? Now look at the people's ideas.

And your task is gonna be to explain what is incorrect about what each pupil's idea.

So each pupil has made a mistake and you need to explain what that mistake is and maybe what it should be instead.

So Jacob says, "In June, the temperatures in Japan and New Zealand will be similar as they're a similar distance from the equator." What's wrong with that? What should it be instead? And Laura says that, "In June, it will be winter in both Japan and New Zealand as they're both on the opposite side of earth to the UK." What's wrong with that and what should it be instead? So pause the video now, take your time with this one.

Think really carefully and then write your answer about what you think is wrong or which part of each student's statement is wrong and what it should be instead.

Off you go.

Well done for your effort on that task.

Time for some feedback now.

So Jacob's statement.

Jacob has forgotten that earth's tilts means that countries that are the same distance north and south of the equator like Japan and New Zealand will experience different heating effects from the sun, so will have different seasons at the same time.

In fact, Japan is in the northern hemisphere like the UK, so in June, it will be be summer.

Whereas, New Zealand is in the southern hemisphere.

So in June, it will be winter, the opposite to Japan and the UK, opposite to the northern hemisphere 'cause New Zealand's in the southern hemisphere.

So they'll actually have different temperatures 'cause they'll have different seasons because of Earth's tilt in June.

Well done if you've got an answer along those lines, it doesn't have to be identical to mine.

Now I suppose you could actually say exactly the same thing about Laura.

Japan and New Zealand are the same distance north and south of the equator roughly, so will experience different heating effects from the sun because of earth tilt, so will have different seasons.

So they won't both have winter, they'll have different seasons.

Here's what I've written.

In June, it's summer in northern hemisphere countries such as the UK and Japan, since the northern hemisphere is tilted more towards the sun.

However, in June, it will be winter in New Zealand and other southern hemisphere countries since at this time, the southern hemisphere is tilted away from the sun.

And the interesting mistake that Laura has made here is she's got confused about this idea of opposite side of the earth to the UK.

Countries will only have the opposite season to the UK if they're on the opposite side of earth to the UK in the sense of being in the southern hemisphere because the UK is in the northern hemisphere.

It's not enough to just be on the opposite side of earth.

It has to be in the opposite hemisphere, out of northern hemisphere and southern hemisphere, to be the opposite season.

Here's a summary of today's lesson.

In summer, compared to winter, there are more hours of daylight, the sun appears higher in the sky and temperatures are warmer.

And that's true for all countries where there's a warmer season called summer and a colder season that gets called winter.

When it's summer in northern hemisphere countries, it's winter in southern hemisphere countries.

What's the reason for that? Well, this occurs because earth spins on an axis that is tilted at an angle of 23.

5 degrees and that causes, in June, the northern hemisphere to be tilted towards the sun, so has summer, and the southern hemisphere to be tilted away from the sun, so has winter.