Lesson video

Hello and welcome to this lesson on our solar system.

This is from the unit called, "Our Solar System and Beyond." My name's Mr. Norris.

This is another lesson where we get to go out into space and see what's out there.

I'm sure many of you watching this might have already a good idea about what the solar system is and what's in the solar system and what's not in the solar system.

And for others of you, there'll be lots of new learning in this lesson.

So whichever one of those is you, let's get going and let's learn about the solar system.

The outcome of this lesson is, you'll hopefully, by the end of it, you'll be able to describe our solar system, including ideas about the locations, movements, sizes and distances apart of different objects within our solar system.

Here are some key words which we'll be talking about this lesson, star, planet, dwarf planet, asteroid, and solar system.

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

This lesson is divided into two parts.

The first section introduces our solar system and the objects within it and the second section looks at size and scale in our solar system.

So let's get started with the first section, our solar system.

So we know that Earth is a planet that orbits the sun.

There's a little diagram of that on the screen now, of course that's not to scale.

We'll talk about scale in the second section of the lesson.

Let's talk about the sun for a moment.

The sun is a star.

Stars are extremely large and extremely hot.

They give out light and other radiation in all directions and in future units you'll learn about other kinds of radiation which are like light, given out by stars.

And it's important to realise that stars are not burning gas.

Some people will sometimes describe star as a giant ball of burning gas.

Stars are made of gas, but it's not burning.

Burning needs oxygen and there's no oxygen in space for gas to burn with.

So the high temperatures within stars are caused by nuclear reactions, not gas burning, which would mean reacting with oxygen.

It's nuclear reactions which occur inside stars.

Let's talk a bit more about Earth as a planet.

So planets are objects that meet three criteria.

So there are three things that an object has to meet for it to be called a planet.

Let's look at them.

So the first criteria an object has to meet to be a planet is it has to orbit a star.

But that's not enough by by itself to make something a planet, to be a planet, the object also has to be so big that its own gravitational pull has pulled all its mass together into a sphere, the most symmetrical shape.

But to be a planet, there's a third criteria that has to be met as well.

To be a planet, an object also has to be so big that its gravitational pull has cleared its orbit of similar sized objects.

So what does that mean? Well, that means as a planet is orbiting, if there's smaller objects nearby, a planet's gravity will attract those smaller objects towards the planet and then there'll be no smaller objects in the planet's path.

But that only happens if an object is big enough that its gravity is strong enough to attract those smaller objects out of the way of its path and clear its path.

So there are the three criteria that something has to meet to be a planet.

Something must have to orbit a star, be so big that gravitational pull makes it a sphere or rounded and something that also has to be so big that it's gravitational pull has to have cleared the orbit of similar sized objects.

The reason we have these three criteria for an object to be a planet is because if we didn't have those three criteria, if planets were just anything that orbited a star, there'd be tens of thousands, if not hundreds of thousands of planets, in the solar system.

And we wanted to keep a planet as kind of a big important object in the solar system.

We don't wanna include those smaller objects or those smaller objects as planets as well.

Let's just check that the Earth meets those criteria, the Earth orbits a star, the sun, the Earth is so big that it's own gravity has made Earth a sphere or rounded.

That's correct.

And that Earth is so big that Earth's own gravitational pull has cleared Earth's orbit of similar sized objects.

That's true as well.

So that's why Earth meets the definition of a planet.

Couple of extra things about planets.

Planets are usually far smaller than the star they orbit and that's definitely true of Earth, which is far smaller than the sun.

Remember that diagram is not to scale on this slide.

And the final thing is that planets are not as hot as stars.

So planets do not give out their own light, of course, stars do give out their own light, 'cause of the nuclear reactions happening within them.

Quick check on what we just talked about.

What are the three main differences between stars and planets? Can you fill in the three gaps? One, two, and three.

Pause the video if you need to and try and fill in the correct words.

Off you go.

Let's see how you got on, number one, stars give out their own light and planets do not give out their own light.

Planets tend to reflect the light of stars.

That's why one side of the Earth that's closest to the sun is lit up and the other side is not lit up, because it's furthest from the sun.

It's the other side from the sun.

Number two, planets orbit around stars.

That's the difference between planets and stars.

Planets orbit around stars, it's not the other way around.

Stars don't orbit around planets, it's planets that orbit around stars.

And number three, stars are usually far bigger than planets.

Well done if you've got those.

So as well as Earth, there's seven other planets that orbit the sun in our solar system and you might know a lot of their names.

We'll talk about those in a minute.

Many planets also have moons orbiting around them.

Earth has just got one moon, but other planets have more than one and some planets have no moons at all.

Then there are also dwarf planets and asteroids in orbit around the sun in our solar system too.

We'll talk about those in more detail in just a moment.

So this system of objects orbiting the sun, planets, dwarf planets and asteroids, that's called our solar system.

That's what our solar system is.

It's called the solar system, 'cause it's based on the Latin word, (Mr. Norris speaking a foreign language) Means sun, so solar system is the system of objects orbiting the sun.

So here's a bit more about the eight planets of our solar system.

They're all different sizes and they're made of different materials.

We've got Mercury, Venus, Earth and Mars, and then Jupiter, Saturn, Uranus, and Neptune, the eight planets of the solar system.

And the eight planets all orbit the sun in circles and all in the same direction.

Each planet also orbits the sun at a different distance.

So you've got each planet orbits in a circle within the orbit of another planet, until you get to Neptune, which is the last planet orbiting in a circle around the sun, with the sun at the centre.

It is important to realise that the circular orbits of the planets, they all lie on the same flat surface.

So it's not like one planet is orbiting this way and another planet is orbiting this way, they're all orbiting on the same flat surface, which is why you can have that view that's just appeared on the screen now of the solar system.

And another thing, it's very important to say, the planets in the solar system are not in a line.

They're often drawn in a line in pictures so it's easier to see them all and you can see that they're in the correct kind of order of distance from the sun, but the planets are not in a line.

The planets are all at different points around their own circular orbits at different distances from the sun, which is more complicated than being in a line, but that's how it is.

So if the planets are presented in a line, which they often are, sometimes, remember that that doesn't show their actual locations.

This only shows their order of their orbits from the sun and the sizes of the planets and the distances between them are not shown to scale and remember, we're gonna talk about scale in the second section of the lesson.

So the four inner planets in order of their distance from the sun, Mercury, Venus, Earth, and Mars, they're smaller and rocky planets, they're made mostly of different kinds of rock.

Whereas the outer planets are larger and they're made of gas.

And it's each planet is so much gas that that gas has so much gravity that it stays all in one place as a planet and doesn't just float off like gas does on Earth.

The planets are so big, there's so much gas, that the gravity of all that gas keeps that gas in a spherical shape and that's the planet, a gas planet like Jupiter, Saturn, Uranus, and Neptune.

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

So for each of the following words or phrases, there's 10 of them, state whether they apply to stars, planets, both or neither.

So for each one of those, one to ten, you just need to decide, does that apply to stars, planets, both or neither? Pause the video now, have a go at that.

Off you go.

Let's see how you got on.

So number one, spherical.

Well that applies to both stars and planets.

Both stars and planets are spherical.

Number two applies to neither, both stars and planets os spherical, neither is the shape of a star.

So stars are not star shaped, stars as spherical.

The reason why we have this shape that we call a star shape when in fact stars are really spherical is because stars can appear that shape to our eyes due to factors that affect our vision, but stars are really spherical.

Number three, rock, that can only apply to planets, but it doesn't apply to all planets, but it can apply to planets.

Gas can apply to both.

You can have planets which are made of gas and stars are very, very hot gas, so hot because of the nuclear reactions happening within them.

On fire applies to neither, because whole planets are not on fire and neither are stars.

Stars are hot, because of the nuclear reactions that happen within them, which is also why they give out light.

So stars give out light, whereas planets don't, planets only reflect light, that was number six and number seven.

Now number eight and number nine, you kind of had to look at together, because planets are very big and stars are extremely big.

Now I understand those words are a little bit vague.

You can have bigger planets than others and you can also have bigger stars than others.

But generally speaking, stars are far bigger than planets.

So that was the way round I put eight and nine and number 10, other objects can orbit around them.

Well let's think about stars and planets in turn, can other objects orbit around stars? Well yes, planets and asteroids and dwarf planets.

Can other objects orbit around planets? Yes moons, so actually that applies to both.

So well done if you got lots of those correct.

Let's talk about the other objects in the solar system now, dwarf planets first.

So dwarf planets are not quite big enough to be planets.

So they're big enough that their gravity makes them round, but they're not big enough that their gravity's cleared their orbits.

There might be other objects still within their orbit.

So for example, you might have heard of Ceres, Ceres is a dwarf planet that orbits the sun between the orbits of Mars and Jupiter, so that's shown in the diagram.

And you might also have heard of Pluto, Eris, Sedna, and Makemake amongst others.

They're just a selection of dwarf planets that orbit beyond Neptune, so further away from the sun than Neptune.

So Neptune is not the edge of the solar system.

And we don't know how many dwarf planets there are in total, because they're small and very far away.

Lots of them are further away than Neptune, so they're hard to see.

Finally, let's talk about asteroids.

There's what's called a belt of asteroids between the orbit of Mars and the orbit of Jupiter.

And it's called a belt of asteroids, because it goes all the way around the sun in a circular shape at that point in the solar system, between the orbit of Mars and the orbit of Jupiter.

And beyond Neptune, there's actually another large belt of asteroids called the Kuiper belt.

And those two places, the asteroid belt and the Kuiper belt, they're not the only places in the solar system where there are asteroids, but they are large collections of asteroids at those places.

So what are asteroids? Well, they're smaller objects than dwarf planets.

So their gravity's not made them round, nor has it cleared their orbits, 'cause their gravity's is not strong enough, 'cause they're smaller objects.

So they can't count as dwarf planets and they certainly can't count as planets.

So just remember in this picture that the planets are not in a line.

That picture just indicates kind of the belt of asteroids in a circular loop around the sun between the orbit of Mars and the orbit of Jupiter.

So let's do a check now about what we've learned about different objects in the solar systems, specifically planets, dwarf planets and smaller objects like asteroids.

So in the table, you just need to use the words yes and no to complete the table showing the difference between planets, dwarf planets and smaller objects like asteroids.

And the first row is done for you.

So pause the video now, just use the words yes or no in each box to try and complete the table, off you go.

Let's see how you got on.

So a planet is so big that its own gravity makes it the sphere or rounded and it's so big that its own gravity has cleared its orbit.

Now a dwarf planet is a bit smaller, so it's still round, but it's not so big that its gravity has cleared its orbit, so that's what a dwarf planet is and then a smaller object like an asteroid is not necessarily round or spherical, 'cause it's not big enough that its own gravity has made it spherical or rounded.

And similarly, it's also not so big that gravity has cleared its orbit.

So that's the difference between these three kinds of object, planets, dwarf planets and asteroids that can orbit stars or in our solar system, three kinds of objects which are orbiting the sun, planets, dwarf planets and asteroids, that's the difference between them.

Quick word about how planets can appear from Earth.

Some planets can sometimes be seen from Earth in the night sky, but if you don't have a telescope, a planet will often just look like a particularly bright star in the night sky, for example, that, maybe, could be, a planet, a particularly bright star in the night sky.

You could maybe use an app or a book or the help of an experienced astronomer to identify if an object in the night sky is just a particularly bright star or whether it is a planet or not.

So the word planet comes from the Greek word, (Mr. Norris speaking a foreign language) which means wanderer.

And that's because planets in the night sky appear to move very, very slowly across the pattern of stars in the sky.

But we now know that the planets in our solar system do not move amongst the stars, even though that's what it looks like in the night sky.

The planets in our solar system orbit one star, the sun and the other stars we see in the night sky are not part of our solar system at all, they're over 10,000 times further away than Neptune.

And the reason why from Earth, planets can look like bright stars in the night sky is because they reflect the sun's light, they don't give out their own light.

Let's do a quick check on this learning cycle, which picture best shows how the planet move around the sun? A, B, C, or D? Choose now, five seconds.

I'm sure you will have chosen the correct picture, which is picture C.

The planet's move around the sun, not amongst the stars like in picture A, not in a line like in picture B, not all on the same orbit, like in picture D, the planets all move around the sun in their own circular orbits with the sun at the centre, like in picture C.

Well done if you chose that.

Time for you to do a task on everything you have learned so far.

All you need to do please, is complete the table to describe the different objects that our solar system consists of.

Stars, planets, moons, dwarf planets and smaller objects like asteroids.

So for each of those objects, I want you to describe what it is in the description column, I'd like you to say how many are there in our solar system and then you need to describe where they're found in our solar system.

You should pause the video now and have a good go at that task with your best effort.

Off you go.

Welcome back, well done for your efforts on that task.

Here's some feedback, don't worry if your answers aren't exactly the same as mine, as long as they're along the right lines.

But as I'm going through, you could pause the video and add anything you need to that improves your table.

So for the description of a star, something like an extremely large sphere of hot gas that gives out light.

How many stars in our solar system? Well just one, the sun.

And where is that star found in our solar system? Well, there's just one, which is at the centre of the solar system, which is the sun.

Planets, the description would be a very large sphere of rock or gas that orbits of star.

There's eight planets in our solar system and I've given their names as well.

And the planets are found orbiting the sun in circles at different distances.

What about moons? Moons are large natural objects that orbit planets.

How many moons are there in the solar system? Well, you didn't have to put an exact number, I've just put lots and I've given some examples.

Earth has one moon and other planets have many and some planets have no moons at all.

And where are moon's found in our solar system? Orbiting planets.

Dwarf planets, the description would be a large round object orbiting a star, but it's not big enough to have cleared its path, so it's not big enough to be a planet.

So something along those lines would be great.

How many dwarf planets are there in the solar system? Well again, we didn't need to give an exact number for this, many and it's not known how many.

And where are dwarf planets found in the solar system? Well there's at least one orbiting in the asteroid belt and other dwarf planets orbit the sun beyond Neptune.

you could have said in the Kuiper belt or beyond.

And finally, smaller objects such as asteroids, they are smaller objects in orbit around stars.

How many are there in the solar system? A huge number.

And where are they found? Well many are found in the asteroid belt between the orbit of miles and Jupiter and the Kuiper belt, which is beyond the orbit of Neptune.

But others are found across the solar system, just not in as big a numbers as they're found in the asteroid belt and in the Kuiper belt.

Very well done for your efforts on that task and in adding any extras to your table that improves your understanding and knowledge, well done.

So that completes the first section of the lesson on the solar system, but the thing we've not talked about yet is the size of the different objects we've talked about and the scale of them within our solar system.

Let's do that now.

So the first thing to say is that space is very, very big and in fact it's so big, that it's really difficult to even get your head round and to imagine the sizes and distances involved.

For example, if Earth was this size, the moon would be this size and those sizes are roughly to scale.

That shows the diameter across the Earth and the diameter across the moon, 3,500 kilometres, compared to Earth's 12,700 kilometres across.

However, the moon orbits Earth at a distance of about 380,000 kilometres.

So that is not the correct distance apart, even though they are the correct sizes.

So let's see if we can do that.

So this slide now shows the moon's distance from Earth with both objects at the correct scale.

So that's a distance of 380,000 kilometres, compared to the size across the Earth and the size across the moon.

And this slide shows the moon's orbit of Earth at the correct scale, so it's showing the full orbit now.

So Earth would be this big and moon would be that big at that distance, orbiting the Earth.

So if you imagine for a moment just look around the room and think about how big the Earth is that we are sat on and stood on and if that entire Earth was shrunk down to the size on the screen now, then that's how far away the moon would be.

So think about what that distance actually represents on the screen between the Earth and the moon, a huge distance, 380,000 kilometres.

But the sun is far bigger than the Earth.

For example, if the sun was this size, Earth would be that size on the screen, tiny in comparison.

But again, the distance between the two isn't to scale.

The sizes are to scale, but not the distance between them.

How could we represent the distance between them? Let's have a go.

So Earth is about 107 sun-widths away from the sun.

So if you look at the width of the sun on the screen, 107 of those widths of the sun would be how far away that minuscule Earth would be at this scale.

So on the screen that I'm looking at, this sun is 15 centimetres across, so I'm just looking at my computer screen.

So I've put a ruler up against the screen and measured that that sun is 15 centimetres across on my screen.

Now 15 centimetres is 0.

15 metres and then we know that Earth is about 107 of those sun-widths away from the sun.

So at this scale, if I do 107 times the width of the sun on the screen, then I found out that that's just over 16 metres.

So on the scale as I'm looking at my screen, Earth, as shown by that tiny dot, representing the size of Earth at this scale, would have to be 16 metres away from the sun.

That's a distance that's bigger than most rooms. Now I want you to do the same calculation, but for the sun as it appears on your screen right now.

So what you need to do is get a ruler or a metre rule to measure the width of the sun or that picture of the sun as it appears on your screen.

So the big yellow sphere of the sun on the screen, measure it now using a ruler, how wide is it on your screen? And then once you've got a number in centimetres, turn into metres just like I did.

So I've got 15 centimetres that turns to 0.

15 metres, but you need to do it for your measurements.

And now if you do 107 times your measurement in metres of how wide that sun is, that's how far away this Earth would have to be from the sun as it appears on your screen in front of you right now.

So you should pause the video now, make that measurement, do that calculation and just take a moment thinking about how small the Earth is and how big that distance is, which you've come up with for how far away that Earth would have to be from that sun as it appears on the screen.

Pause the video now to do that.

what you probably found out from doing that calculation is that our solar system is so large that if you imagine trying to draw it with the distances to scale, all of the objects would actually, pretty much, become too small to see.

So here is a picture of the solar system that attempts to show the scale of our solar system more accurately than many pictures online or in books.

So take a moment, perhaps pause the video and take a good look at that picture.

Now, you can see the sun in the centre, you can see the asteroid belt, there is an arrow pointing to where Earth would be.

The orbits of the other planets are shown.

Pluto's orbit is shown, 'cause that's at a funny angle, 'cause Pluto is a dwarf planet and the Kuiper belt is shown.

So what you perhaps should have spotted from studying that picture is that on this scale, the planets are too small to see.

That's why they've not been drawn.

That's why the arrow pointing to Earth doesn't look like it's pointing at anything, because Earth is there, but just on this scale, on the accurate scale, it's too small to see, so it's not being drawn.

And the same with the other planets.

We've added lines to mark the orbits of the planets, but remember those circular lines are not really there.

They've just been added to mark the orbits of where the other planet's orbit the sun.

And actually, this picture isn't perfect, because the sun has not been drawn to scale.

In the picture, the sun is shown much bigger than it really would appear in the solar system.

So here's an analogy to try and get our heads around size and scale in the solar system a bit more.

If our solar system was the size of a large football stadium, like the one in the picture, then the sun would only be about the size of a tennis ball on the centre spot.

So imagine, you might just be able to see a tiny speck on the centre spot, the size of a tennis ball.

Mercury, Venus, Earth and Mars would each fit on the head of a pin and Earth would orbit just within the centre circle line, if the sun was a tennis ball on the centre spot.

But Earth would fit on the head of a pin, compared to the size of the solar system.

And all of the other planets, so Jupiter, Saturn, Uranus, Neptune, would be less than one centimetre across, orbiting in circles around that centre spot, the tennis ball sun at the centre spot and Neptune, the furthest planet that would orbit, so it'd be less than one centimetre across, orbiting at the distance of the furthest seats.

So that analogy, hopefully, perhaps gives a better sense of scale of the sizes of the sun and sizes of the planet and the distances of the orbits within the solar system.

So let's do a check if you've got the right idea about the right sense of scale here.

So if the sun was the size of a standard football, which would best represent Earth? Would it be a tennis ball about five metres away from a football sun? Would it be a pea about 12 metres away, that's half a tennis court from a football sun? Or would Earth be best represented by a mustard seed about 24 metres away, so the full length of a tennis court, away from a football sun? Which gives the most accurate representation of the scale of the sizes and distances of the sun and Earth? A, B, or C, take a moment to decide.

The correct answer is C.

If the sun was the size of the football, the Earth would be best represented, from these three options, by a mustard seed about 24 metres away from a football sun.

That's the sizes and scales and distances we're talking about in space and in the solar system.

And Neptune would orbit in a circle about one and a 1/2 kilometres across, with the football sun at the centre.

Time to put together this learning about size and scale in our solar system.

So there's another table to fill in for this task, but this table is about the two pictures.

So take a moment to have a good look at picture one and have a good look at picture two.

So in this table I would like you to explain what each picture shows well and what each picture does not show well about our solar system.

Now, the first row of the table is for both.

So you might think about first, what do both pictures show well and what do both pictures not show well? Then you could look in more detail at picture one.

What does picture one show particularly well and what does part picture one really not show well? And then the same for picture two.

So pause the video now and have a good think and then fill in that table with your best effort.

Off you go.

Welcome back and well done for your efforts on that task.

Here's some feedback and don't worry again, if your answers don't look exactly like this as long as they're along the right lines and you can always add to your table as I'm giving feedback to improve your work.

So what do both pictures show well? Firstly, the order of the planets is shown well by both pictures.

And the idea that the four inner planets are smaller than the four outer planets, well that's shown on both pictures.

But what does neither picture show well? Well, the sizes of the planets and the sun are not drawn to scale.

So if they were drawn to scale, they'd be too small.

The distances between the planets and the sun are far too close for the sizes they've been drawn and dwarf planets, moons and the Kuiper belt are not shown.

Now let's talk about picture one.

What did picture one show? Well, picture one at least showed the asteroid belt between the orbits of Mars and Jupiter, picture two didn't do that.

But picture one shows the planets in a line and that's not correct.

I'd have hoped you'd have included that one, spotted that one.

What about picture two? Picture two shows the planets at different points around circular orbits, which is correct, but picture two included stars, kind of in the background or kind of between the orbits of the planets.

Go back and look at the picture if you're not sure what I mean, if you didn't spot that.

And in the picture it's unclear whether the other stars that are shown are they within the solar system? Well they're not.

Or are they in the background, which is where they're supposed to be and the picture doesn't make that clear.

Also, picture two doesn't show the asteroid belt or the Kuiper belt.

So well done if you identified lots of the good points and bad points of each picture there, well done.

So that's the end of this lesson on the solar system.

Here is a summary.

So firstly, stars are extremely large spheres of hot gas that give out light, not because they're burning, because of nuclear reactions.

And the sun is a star.

And our solar system refers to the sun and all the objects in orbit around the sun.

This includes the eights planets and their moons, dwarf planets and smaller objects such as asteroids.

And finally, the distances between objects in our solar system are very, very large compared to the sizes of the objects.