0:00:11 > 0:00:16- Hi, I'm Jem.- And I'm Helen. And we are mad about science.
0:00:16 > 0:00:20There's just so much to find out about the planets and the stars.
0:00:20 > 0:00:23We thought we'd show you of our favourite demonstrations
0:00:23 > 0:00:26to help you understand how the solar system works.
0:00:26 > 0:00:27'Coming up in today's show,'
0:00:27 > 0:00:30Blue Peter stars Helen and Barney
0:00:30 > 0:00:33set us six sensational stargazing challenges.
0:00:33 > 0:00:36I wonder how the Earth, sun and moon move around each other.
0:00:36 > 0:00:38Why do we have seasons?
0:00:38 > 0:00:40I'd actually like to know how to make my own rocket.
0:00:40 > 0:00:43With our young astronomers' help, we work on teasers,
0:00:43 > 0:00:46including how the Earth orbits the sun.
0:00:46 > 0:00:48It can't be that difficult.
0:00:48 > 0:00:51The Earth does it all day every day and never complains.
0:00:51 > 0:00:55- Discover why we see the moon in different shapes.- I've got it!
0:00:55 > 0:00:58And reach for the stars as we make a home-made rocket.
0:00:58 > 0:01:00Wow, that would be awesome!
0:01:05 > 0:01:08I'm here at the observatory in East Sussex,
0:01:08 > 0:01:11and I've got lots of young astronomers here to help me out.
0:01:11 > 0:01:14Come on down. We've got our challenge. Come and have a look.
0:01:15 > 0:01:20The distances between the planets are so massive it's hard to picture them.
0:01:20 > 0:01:25What is the best way to describe the distances involved?
0:01:25 > 0:01:27Can anyone tell me what the planets are?
0:01:27 > 0:01:30Mars, Venus, Earth, Mercury,
0:01:30 > 0:01:33Uranus and Saturn.
0:01:33 > 0:01:36And Jupiter. And Neptune.
0:01:36 > 0:01:37Almost there. That's brilliant.
0:01:37 > 0:01:40Does anyone know which is the furthest planet from the sun?
0:01:40 > 0:01:43- Neptune.- That's right, yes.
0:01:45 > 0:01:48The solar system is made up of eight planets.
0:01:48 > 0:01:52The four rocky planets are Mercury, Venus, Earth and Mars.
0:01:52 > 0:01:57Jupiter, Saturn, Uranus and Neptune are known as the gas giants.
0:01:57 > 0:01:59The temperature of a planet
0:01:59 > 0:02:01is affected by how close to the sun it is.
0:02:01 > 0:02:05The temperature on Venus can get up to 460 degrees Celsius,
0:02:05 > 0:02:07hot enough to melt metal,
0:02:07 > 0:02:12while the temperature on Neptune is minus 220 degrees Celsius.
0:02:12 > 0:02:16The problem we have is that the size of the planet is tiny
0:02:16 > 0:02:19compared with the enormous distances between them.
0:02:19 > 0:02:23But I have a system that will help us understand those two things.
0:02:23 > 0:02:26For that, I'm going to need some fruit
0:02:26 > 0:02:29and some spices and some loo roll.
0:02:29 > 0:02:33My solution to this challenge is a loo roll solar system.
0:02:33 > 0:02:35We need to know how big the planets are.
0:02:35 > 0:02:37What's the biggest planet?
0:02:37 > 0:02:40- Jupiter.- It is Jupiter. Now what's the biggest piece of fruit
0:02:40 > 0:02:43you think we could use to represent Jupiter?
0:02:43 > 0:02:44- Watermelon.- It is.
0:02:44 > 0:02:48We'll use a watermelon to represent Jupiter because that's large.
0:02:48 > 0:02:52What's a small thing we could think of to represent the smallest planet?
0:02:52 > 0:02:55- Grape.- A grape. A grape's not bad.
0:02:55 > 0:02:59- Can anyone think of anything smaller than a grape?- A raisin.
0:02:59 > 0:03:02Getting close. What we're going to use is a peppercorn.
0:03:02 > 0:03:05A tiny, tiny little thing for the smallest planet.
0:03:05 > 0:03:08As our young astronomers gather the essential equipment,
0:03:08 > 0:03:10there's one thing missing.
0:03:10 > 0:03:14Now, the sun is 99% of everything in the solar system.
0:03:14 > 0:03:17So, all of the planets and the comets and asteroids
0:03:17 > 0:03:22only make up a tiny fraction - 1% - of everything.
0:03:22 > 0:03:27So, our sun, compared with what's in everyone's hands, is massive.
0:03:27 > 0:03:31We've got another young astronomer who's going to bring it out to us.
0:03:31 > 0:03:33Alex, you can bring it out now.
0:03:33 > 0:03:37# Rubber ball I come bouncing back to you
0:03:37 > 0:03:42# Rubber ball, I come bouncing back to you-u-u-u-u. #
0:03:42 > 0:03:44BOING!
0:03:46 > 0:03:48So, I've got my loo roll ready
0:03:48 > 0:03:51to measure the distances of the solar system.
0:03:51 > 0:03:57Each piece of toilet roll represents 16 million kilometres.
0:03:57 > 0:03:59It's a long, long way.
0:03:59 > 0:04:03The first planet, Mercury, is 3.5 pieces of toilet roll in.
0:04:03 > 0:04:07So, Mercury, hold out your planet so we can see what have you got there?
0:04:07 > 0:04:10The peppercorn. The next planet is Venus,
0:04:10 > 0:04:14which is one, two, just around three further out.
0:04:14 > 0:04:18So we've got Venus. What have you got? A cherry tomato for Venus.
0:04:18 > 0:04:21The next planet is us - it's Earth.
0:04:21 > 0:04:24We're about 2.5 pieces of toilet paper further out.
0:04:24 > 0:04:27Put your foot on that and hold out the Earth.
0:04:27 > 0:04:30The last rocky planet is Mars.
0:04:30 > 0:04:33That is five pieces further out.
0:04:33 > 0:04:34Here you go.
0:04:34 > 0:04:37Now, these are all the rocky planets.
0:04:37 > 0:04:40We're heading out into the asteroid belt.
0:04:40 > 0:04:42The next planet is much further away.
0:04:43 > 0:04:478, 9, 10, 11, 12...
0:04:47 > 0:04:5131, 32, 33, 34.
0:04:51 > 0:04:54So, now we're ready for the first of the gas giants, Jupiter.
0:04:54 > 0:04:57The biggest planet in the solar system. OK.
0:04:57 > 0:05:00So we're going to keep going out now towards Saturn.
0:05:00 > 0:05:0535, 36, 37, 38, 39, 40.
0:05:05 > 0:05:07Saturn. Hold out your planet.
0:05:07 > 0:05:10So, we got a grapefruit representing Saturn,
0:05:10 > 0:05:16which is 1.4 billion kilometres away from our sun over there.
0:05:16 > 0:05:18We've got further to go, so let's keep going.
0:05:21 > 0:05:2588, 89, 90.
0:05:25 > 0:05:29We've got to Uranus. Brilliant! We've got one more planet to go.
0:05:29 > 0:05:32This one is even further that way.
0:05:32 > 0:05:34Off we go!
0:05:39 > 0:05:42So we've come to the end of the second roll of toilet paper
0:05:42 > 0:05:45but there are only 20 more squares needed.
0:05:45 > 0:05:48So we're going to have the next one.
0:05:52 > 0:05:56So here we are - our last planet - Neptune. Represented by a lime.
0:05:56 > 0:06:03This is 280 squares of loo roll down the line from the sun.
0:06:03 > 0:06:08In the solar system, that distance is 4.5 billion kilometres,
0:06:08 > 0:06:11and this isn't even the edge of the solar system.
0:06:11 > 0:06:13It's just where the last planet out is.
0:06:18 > 0:06:21In fact, the planets are very rarely lined up like this.
0:06:21 > 0:06:24They're all spread out, going on their orbits around the sun.
0:06:24 > 0:06:27But the experiment gives you an idea
0:06:27 > 0:06:29of the distances between those orbits.
0:06:29 > 0:06:31So, that's our challenge complete.
0:06:31 > 0:06:35Hopefully you've now got an idea of the size of the solar system
0:06:35 > 0:06:37and the scale of the planets.
0:06:37 > 0:06:39Hopefully it's also something
0:06:39 > 0:06:42you can try for yourself at home or at school.
0:06:47 > 0:06:49We're at Herstmonceux Observatory,
0:06:49 > 0:06:52waiting for another challenge to come through.
0:06:52 > 0:06:56I've got my junior astronomers - Ellie, Matthew and Kain.
0:06:56 > 0:06:59I've got our challenge coming in right now.
0:06:59 > 0:07:02I love watching rockets blast off into space.
0:07:02 > 0:07:06In fact, I'd actually like to know how to make my own rocket.
0:07:06 > 0:07:09So, rather than me getting my hands dirty,
0:07:09 > 0:07:12I'd like you to make me a rocket.
0:07:12 > 0:07:14Yeah, that would be awesome!
0:07:14 > 0:07:16You don't get a better challenge.
0:07:16 > 0:07:19I've made a few rockets. It's always exciting.
0:07:19 > 0:07:22How high might a rocket need to go to get to the edge of space?
0:07:22 > 0:07:24Millions of miles.
0:07:24 > 0:07:26Millions of miles.
0:07:26 > 0:07:30Believe it or not, it's only about 20 miles. Up to the edge of space.
0:07:30 > 0:07:33When was the first rocket launched up to space?
0:07:33 > 0:07:37Well, the first one that was powerful enough to get up into space
0:07:37 > 0:07:40was made by the Germans in the 1940s.
0:07:40 > 0:07:43It was called a V2 rocket.
0:07:43 > 0:07:46However, people have always played with launching things.
0:07:46 > 0:07:51Chinese gunpowder rockets are the basis of modern-day rocketry.
0:07:51 > 0:07:53They were invented in the 13th century.
0:07:53 > 0:07:58700 years later, rockets enabled us to get to the moon.
0:07:58 > 0:08:02Five, four, three, two, one...
0:08:07 > 0:08:10The thrust from the space shuttle at takeoff is greater than that
0:08:10 > 0:08:13from 30 jumbo jets put together.
0:08:15 > 0:08:20For today's challenge, we need some little camera film cases.
0:08:20 > 0:08:25We need some water. We need some kind of fizzy vitamin tablets
0:08:25 > 0:08:27and probably some card and scissors.
0:08:27 > 0:08:30- Do you reckon you can get that? - I know where to get them.- OK, go on.
0:08:48 > 0:08:50So, how does it actually work?
0:08:50 > 0:08:53This water and these tablets,
0:08:53 > 0:08:56they combine together to make the fuel of the rocket.
0:08:56 > 0:08:59When these tablets get dropped in water, they start fizzing.
0:08:59 > 0:09:02That fizzing is them giving off a gas called carbon dioxide.
0:09:02 > 0:09:07Now, if we confine that inside here,
0:09:07 > 0:09:09then the gas pressure keeps building up.
0:09:09 > 0:09:12When the gas pressure gets sufficiently high, bang!
0:09:12 > 0:09:17It bursts the little launchpad off and your rocket heads skywards.
0:09:23 > 0:09:25Oh, are they your fins?
0:09:35 > 0:09:37So, we've got some amazing-looking rockets now.
0:09:37 > 0:09:41But it's the moment of truth. We've got to see how they fly.
0:09:41 > 0:09:44You've got to take the bottom off your rocket.
0:09:44 > 0:09:45Very nice.
0:09:45 > 0:09:49Then you get your fuel tablet, break it up into little pieces,
0:09:49 > 0:09:53- then you've got to decide what's the right amount of fuel.- All of it.
0:09:53 > 0:09:55You've put the lot in. Oh, my life!
0:09:55 > 0:09:58I'm staying this end of the table.
0:09:58 > 0:09:59The next big decision
0:09:59 > 0:10:02is to decide how much water you're going to put in.
0:10:02 > 0:10:03Water does two jobs.
0:10:03 > 0:10:06One, it reacts with the rocket fuel to produce the gas.
0:10:06 > 0:10:09The other, it provides the weight,
0:10:09 > 0:10:12the mass for the rocket to throw out the back, to jet itself forwards.
0:10:12 > 0:10:16- I'm cunningly watching what you guys do.- Three quarters.
0:10:16 > 0:10:18Yours is going to go off pretty quick.
0:10:18 > 0:10:22You don't want to lose that power, so make sure your lid is handy,
0:10:22 > 0:10:26and, as quickly as possible, put the lid on and jam it closed.
0:10:26 > 0:10:29As soon as you've done it, turn it over, step back.
0:10:29 > 0:10:33Most rocket engines use either a solid or a liquid fuel.
0:10:33 > 0:10:35This is burned to create hot gas,
0:10:35 > 0:10:38which is forced out the bottom of the rocket.
0:10:38 > 0:10:42This creates an opposite upward force called thrust.
0:10:42 > 0:10:46Our home-made rockets work on a similar principle, creating thrust.
0:10:46 > 0:10:48- Everybody ready to fuel up their rockets?- Yeah.
0:10:48 > 0:10:52This is absolutely crucial now that we get this right. Ready?
0:10:52 > 0:10:55Three, two, one. Lid on.
0:10:56 > 0:10:58I've done it.
0:10:58 > 0:11:01Are you snapped on? Agh, we have a fuel leak!
0:11:01 > 0:11:03There you go, rescued.
0:11:08 > 0:11:10LID POPS
0:11:10 > 0:11:13Aw! Aw! Look at that one!
0:11:13 > 0:11:19Oh, that's fan... Yes. Fantastic!
0:11:23 > 0:11:25There you go, Barney.
0:11:25 > 0:11:28You wanted us to build a rocket, we've just built loads of them.
0:11:28 > 0:11:32They're really not that difficult to make, so I reckon, make them at home,
0:11:32 > 0:11:35make them at school. To be on the safe side, launch them outside.
0:11:35 > 0:11:38That way, the sky's the limit.
0:11:53 > 0:11:57With me are two young astronomers - Tiani and Dzhem.
0:11:57 > 0:11:59They're going to help me with my next challenge.
0:11:59 > 0:12:01Here it is. Let's have a look.
0:12:02 > 0:12:06We've all seen different types of weather at different times of year,
0:12:06 > 0:12:08but why do we have seasons?
0:12:09 > 0:12:13Do you know why it's warmer in the summer and colder in the winter?
0:12:13 > 0:12:16- Is it because of the axis of the world?- It is.
0:12:16 > 0:12:17The Earth has an axis
0:12:17 > 0:12:19that spins around and is tilted over.
0:12:21 > 0:12:26The Earth orbits the sun and is tilted by about 23 degrees.
0:12:26 > 0:12:30Countries near the equator don't have four seasons like we do.
0:12:30 > 0:12:34They often have just two - a wet and a dry season.
0:12:34 > 0:12:36Now to solve this challenge,
0:12:36 > 0:12:38what we've got are some very simple things.
0:12:38 > 0:12:41We need the globe, a torch and some whiteboard markers.
0:12:41 > 0:12:44So, let's get started.
0:12:44 > 0:12:45The torch represents the sun
0:12:45 > 0:12:49and the sun shines sideways at the Earth from over here.
0:12:49 > 0:12:52Can you see, if you come round, you can see that the torch
0:12:52 > 0:12:54is shining a circular light on the globe.
0:12:54 > 0:12:58This torch is giving out fixed amounts of energy.
0:12:58 > 0:13:03All the energy coming from the torch is landing on that circle there. OK.
0:13:03 > 0:13:07What I want you to do is to draw a circle around
0:13:07 > 0:13:10where the light is falling on the earth.
0:13:10 > 0:13:15Can you see an oval? I'm going to try and hold the torch steady.
0:13:15 > 0:13:16You see if you can draw around it.
0:13:21 > 0:13:24Brilliant! So, this is winter.
0:13:24 > 0:13:28In the summer, the Earth has come all the way around the sun,
0:13:28 > 0:13:30all the way around here.
0:13:30 > 0:13:34So, in the summer, Earth is here, and the sun is over here.
0:13:34 > 0:13:38Now, could you draw around the light that falls on the earth now?
0:13:43 > 0:13:46OK, so what's the difference
0:13:46 > 0:13:48between those two shapes in the summer and the winter?
0:13:48 > 0:13:51- The summer's smaller?- That's right.
0:13:51 > 0:13:55So in summer, we only have to share the energy the sun's giving out
0:13:55 > 0:13:57with this smaller area here.
0:13:57 > 0:14:01In winter, we have to share that same energy with all of this
0:14:01 > 0:14:04so we get much less energy for ourselves.
0:14:04 > 0:14:07That's why it's colder in the winter and warmer in the summer.
0:14:07 > 0:14:10Sometimes people think that we have seasons
0:14:10 > 0:14:15because the tilt of the Earth changes direction. That's not true.
0:14:15 > 0:14:18The Earth is always tilted so that the North Pole
0:14:18 > 0:14:20points towards the pole star.
0:14:20 > 0:14:24As it goes around the sun, it still points towards the pole star.
0:14:24 > 0:14:28When it's on one side, it's tilted towards the sun,
0:14:28 > 0:14:31and when it's on the other side, it's tilted away from the sun,
0:14:31 > 0:14:36meaning we get different amounts of light at different times of year.
0:14:36 > 0:14:38So that's the solution to our challenge.
0:14:38 > 0:14:43Hopefully you can try that for yourself at home or at school.
0:14:48 > 0:14:53I've got two assistants, Lauren and Castor.
0:14:53 > 0:14:55We've just got our challenge. So let's have a look.
0:14:55 > 0:15:00I've always wanted to take a closer look at the stars and planets
0:15:00 > 0:15:04but I don't have a telescope. Can I make one at home or at school?
0:15:04 > 0:15:07Have you used telescopes before? Do you know what they're used for?
0:15:07 > 0:15:12Telescopes are useful for looking into space and looking at stars.
0:15:12 > 0:15:14Lots of things to look at out in space.
0:15:14 > 0:15:17I saw a glimpse of Jupiter once at this observatory.
0:15:17 > 0:15:23- What could you see?- It was a big round ball with a red dot on it.
0:15:23 > 0:15:26So, you saw the Great Red Spot of Jupiter,
0:15:26 > 0:15:29like a pimple on the planet. Telescopes are arrangements
0:15:29 > 0:15:32of lenses that we use to look at things out in the sky.
0:15:32 > 0:15:36They use optics. They've been around for hundreds of years.
0:15:38 > 0:15:41The first optical telescope was constructed in 1608
0:15:41 > 0:15:44by the Dutch optician Hans Lippershey.
0:15:44 > 0:15:46His children were playing with lenses
0:15:46 > 0:15:49and realised that when they put two together,
0:15:49 > 0:15:53a faraway church tower appeared much closer.
0:15:53 > 0:15:55The following year, Galileo Galilei
0:15:55 > 0:15:58built the first astronomical telescope
0:15:58 > 0:16:00from a tube containing two lenses.
0:16:00 > 0:16:03With this telescope and several following versions,
0:16:03 > 0:16:06Galileo made the first telescopic observations of the sky
0:16:06 > 0:16:09and discovered mountains on the moon
0:16:09 > 0:16:12and that the Milky Way was actually a huge number of stars.
0:16:12 > 0:16:15Since then, telescopes have increased in size
0:16:15 > 0:16:18and produce much better images.
0:16:18 > 0:16:20There is a special telescope that orbits the Earth
0:16:20 > 0:16:23known as the Hubble space telescope.
0:16:23 > 0:16:26It can photograph objects with ten times more detail
0:16:26 > 0:16:27than Earth-based telescopes.
0:16:29 > 0:16:32Our two astronomers go and collect what we need -
0:16:32 > 0:16:36a selection of lenses of different thicknesses, something to look at,
0:16:36 > 0:16:39some tubes, scissors and sticky tape.
0:16:48 > 0:16:50So now we have all the things we need.
0:16:50 > 0:16:53I'm going to take a pair of magnifying glasses
0:16:53 > 0:16:56and Lauren, could you take those two there?
0:16:56 > 0:16:58What's the difference between those two lenses?
0:16:58 > 0:17:02- One is definitely thicker. - One's thicker than the other.
0:17:02 > 0:17:06What you want is to think about the thick one first.
0:17:06 > 0:17:09We've got a globe over there. That's what we're going to be looking at.
0:17:09 > 0:17:13What we're going to do first is work out approximately
0:17:13 > 0:17:15where our lenses need to be.
0:17:15 > 0:17:19So, what you need to do, is to hold up the thicker one
0:17:19 > 0:17:20and put the thin one behind it.
0:17:20 > 0:17:24Move them around a little bit. Move them further and closer to you.
0:17:24 > 0:17:27- Can you see the globe?- Mmm-hmm.
0:17:27 > 0:17:31- Is it in focus?- Yeah. - What does it look like?
0:17:31 > 0:17:33- It's upside down.- It is upside down.
0:17:33 > 0:17:36That's how telescopes work. You're always seeing upside down.
0:17:36 > 0:17:40Now what we need to do, Castor's going to measure the distance
0:17:40 > 0:17:43between the two lenses when they're in the right place.
0:17:43 > 0:17:46- So, how far apart are they? - 30 centimetres.- Brilliant, OK.
0:17:46 > 0:17:50The next thing you need is a cardboard tube.
0:17:50 > 0:17:53Astronomers can't stand around all night holding lenses.
0:17:53 > 0:17:57Castor's going to take a tube there. I'm going to use the tube here.
0:17:57 > 0:17:59You'll need to do is get some help.
0:17:59 > 0:18:03Get some help cutting slots in the right place in a tube.
0:18:03 > 0:18:05How are you going to make your telescope?
0:18:05 > 0:18:11We're going to take the thicker lens and pop it in this slot.
0:18:11 > 0:18:13And then what happens next, Castor?
0:18:13 > 0:18:19- Then you measure it, put the cardboard bit in.- What's that for?
0:18:19 > 0:18:23That's to hold the glass in place.
0:18:23 > 0:18:25Where should the small lens go down?
0:18:25 > 0:18:28- Here.- OK. Now let's see if we can get the telescope
0:18:28 > 0:18:29to work inside the tube.
0:18:29 > 0:18:31Come back over here.
0:18:31 > 0:18:35Now, this thin lens may not be in exactly the right place first time.
0:18:35 > 0:18:38What you may need to do is just adjust it a bit.
0:18:38 > 0:18:39- Can you see the globe?- Yes.
0:18:39 > 0:18:41Is it in focus or do you think it could be better?
0:18:41 > 0:18:44- In focus. - Perfectly in focus first time.
0:18:44 > 0:18:49- What can you see on the planet, Castor?- I can see all sorts.
0:18:49 > 0:18:52- Can you see any countries?- Yeah. - What do you think, Castor?
0:18:52 > 0:18:56I think it's pretty amazing when you've just made it by home-made.
0:18:56 > 0:18:59- It is pretty good.- It's really easy to do, isn't it?- Yeah.
0:18:59 > 0:19:01How about you, Lauren? What do you think?
0:19:01 > 0:19:02I think it's a good idea
0:19:02 > 0:19:06that you can look at the stars with just a little telescope.
0:19:06 > 0:19:07It makes things bigger.
0:19:07 > 0:19:10All those things that are so far away, makes them seem closer.
0:19:10 > 0:19:13We can't see any stars now because it's still daylight.
0:19:13 > 0:19:16But we're all ready with our home-made telescopes
0:19:16 > 0:19:19to have a look at the cosmos this evening.
0:19:19 > 0:19:22You can do the same if you make your own home-made telescope.
0:19:27 > 0:19:30We're here at an observatory in East Sussex
0:19:30 > 0:19:32with a group of superb young astronomers
0:19:32 > 0:19:35and we're waiting for a challenge to come in.
0:19:35 > 0:19:37It should be coming in any moment.
0:19:37 > 0:19:40I've always wondered how the Earth, sun and moon move around each other.
0:19:40 > 0:19:43People used to think the sun moves around the earth
0:19:43 > 0:19:45but that's not true, is it?
0:19:45 > 0:19:49Does the sun go round the Earth or does the Earth go round the sun?
0:19:49 > 0:19:52- The Earth goes round the sun.- Like I said, superb young astronomers!
0:19:52 > 0:19:57But how far away from the Earth do you reckon the sun is? 100 metres?
0:19:57 > 0:19:59A million kilometres?
0:19:59 > 0:20:01150 million kilometres? What do you reckon?
0:20:01 > 0:20:04150 million kilometres.
0:20:04 > 0:20:08Astonishing! We truly do have superb young astronomers.
0:20:10 > 0:20:15The Earth is orbiting the sun at an amazing 108,000 kilometres per hour.
0:20:15 > 0:20:19That's much faster than the average space rocket.
0:20:19 > 0:20:21Of course, we cannot see the sun at night.
0:20:21 > 0:20:23This is because the Earth's rotating
0:20:23 > 0:20:25at the same time as it orbits the sun.
0:20:25 > 0:20:29So different places on the planet face the sun at different times.
0:20:29 > 0:20:33Seems like a bit of a massive challenge. Are you up for it?
0:20:33 > 0:20:35- ALL: Yes!- Excellent.
0:20:35 > 0:20:39You've got to make yourselves look like the Earth, the moon and the sun,
0:20:39 > 0:20:42and I've got to figure out the rest of it. Come on!
0:20:42 > 0:20:44Whilst the kids are getting ready,
0:20:44 > 0:20:47I'm going to mark out a bit of the solar system.
0:20:53 > 0:20:57This circular path is the one that the Earth's going to have to take
0:20:57 > 0:20:59as it goes round the sun.
0:20:59 > 0:21:01The moon's got a slightly trickier job.
0:21:01 > 0:21:05That's got to orbit the Earth as the Earth orbits the sun.
0:21:13 > 0:21:17That's my orbit. Now all I need are the Earth, the sun and the moon.
0:21:24 > 0:21:27That was the fastest-looking solar system I've seen.
0:21:27 > 0:21:30That's what you guys are going to be - an element of the solar system.
0:21:30 > 0:21:32So, you two in blue,
0:21:32 > 0:21:34Dzhem, Tiani, you're the Earth.
0:21:34 > 0:21:36Now, are you two OK holding hands?
0:21:36 > 0:21:39- Yes.- Yeah? Go on. For the sake of television,
0:21:39 > 0:21:41for the sake of the solar system.
0:21:41 > 0:21:43You have to hold hands and rotate around.
0:21:43 > 0:21:45You both have to spin around.
0:21:45 > 0:21:49How long do you think it takes the Earth to do one rotation -
0:21:49 > 0:21:52- spin on its axis?- One day. - One day! Spot-on.
0:21:52 > 0:21:56That's why it looks as though the sun rises and sets once a day.
0:21:56 > 0:21:58So, come together and start spinning round.
0:21:58 > 0:22:02Oh, beautiful! Round you go.
0:22:02 > 0:22:06No, don't disappear into space. Just come rotating here.
0:22:06 > 0:22:08It can't be that difficult.
0:22:08 > 0:22:10The Earth does it every day and never complains.
0:22:10 > 0:22:14Fantastic! I'm loving that. That's like a day, right.
0:22:14 > 0:22:18Nice spinning. Now we need your satellite, your moon.
0:22:18 > 0:22:22The moon's smaller than the Earth, it's actually quite a lot smaller.
0:22:22 > 0:22:23We'll just have one body as the moon.
0:22:23 > 0:22:27Now, how long do you think it takes you, as the moon,
0:22:27 > 0:22:29to go all the way round the earth?
0:22:29 > 0:22:32- A week?- A week's not bad. A quarter of the way there.
0:22:32 > 0:22:36The other thing is, the moon always keeps its same face to the earth.
0:22:36 > 0:22:39We only ever see one side of the moon.
0:22:39 > 0:22:44While these guys are turning, you go round with them.
0:22:44 > 0:22:46Perfect. Keep looking at them.
0:22:46 > 0:22:49You can go nice and slowly. Don't worry, Castor.
0:22:49 > 0:22:52They have to go round about 29 times faster than you.
0:22:52 > 0:22:54You just sort of keep with them.
0:22:55 > 0:22:59Now, for the most important, in many ways, body in the solar system.
0:22:59 > 0:23:03The thing that holds the solar system together, the sun.
0:23:03 > 0:23:06You go right at the centre of the solar system.
0:23:06 > 0:23:08It's your gravity that stops the planets
0:23:08 > 0:23:09flinging off into outer space.
0:23:09 > 0:23:13You've got an important job. You have to be highly energetic.
0:23:13 > 0:23:15If the Earth and the moon are straying off,
0:23:15 > 0:23:19it's your job to hold them together. So feel free to shout instructions.
0:23:19 > 0:23:23So, you're here, providing energy and encouragement.
0:23:23 > 0:23:28OK. You are simply astonishing, apart from we're going the wrong way.
0:23:28 > 0:23:30Keep spinning round, keep spinning.
0:23:30 > 0:23:33I think you guys are spinning that way.
0:23:33 > 0:23:36Then this is your orbit now.
0:23:36 > 0:23:39You have exactly one year to make it all the way round.
0:23:43 > 0:23:45# Dizzy... #
0:23:45 > 0:23:47Don't crash into the Earth!
0:23:47 > 0:23:51# I'm so dizzy My head is spinning... #
0:23:51 > 0:23:54You see these guys drifting in towards you, it's a disaster.
0:23:54 > 0:23:56The Earth's going to burn up.
0:23:56 > 0:23:58So shout, "No, you're coming to close to the sun!"
0:23:58 > 0:24:03# You're making me dizzy My head is spinning... #
0:24:03 > 0:24:06- Don't come too close to the sun. - You'll burn up.
0:24:06 > 0:24:08You're going to burn up planet Earth.
0:24:08 > 0:24:12# And it's you, girl making it spin... #
0:24:12 > 0:24:14This is brilliant. Keep going, keep going.
0:24:14 > 0:24:19In real life you're supposed to be going 67,000 miles an hour.
0:24:19 > 0:24:21You're coming to close to the sun!
0:24:21 > 0:24:26That was good gravity. You kept them in such a good orbit.
0:24:26 > 0:24:30# Like a whirlpool It's spinning... #
0:24:31 > 0:24:32We finally managed it.
0:24:32 > 0:24:35We've managed to simulate the movement of the planets
0:24:35 > 0:24:37using just six people.
0:24:37 > 0:24:40What we've got going on here is the sun's in the centre
0:24:40 > 0:24:43and its enormous gravity is holding the solar system together -
0:24:43 > 0:24:46stopping the Earth drifting out into space.
0:24:46 > 0:24:49The Earth goes round the sun once a year.
0:24:49 > 0:24:52The Earth rotates on its own axis once a day.
0:24:52 > 0:24:56And the moon goes round the Earth once a month.
0:24:56 > 0:24:59It all goes off in our solar system all the time.
0:24:59 > 0:25:02I think these fellas have done an amazing job.
0:25:02 > 0:25:04It's not easy, but I recommend trying it.
0:25:04 > 0:25:07So, school field, playground, wherever. Best of luck.
0:25:12 > 0:25:15I'm here at the Godlee Observatory in Manchester.
0:25:15 > 0:25:18With me is Luke, who's going to help me with our next challenge.
0:25:18 > 0:25:20Let's have a look what it is.
0:25:20 > 0:25:23Sometimes when you look at the moon it's round,
0:25:23 > 0:25:26but at other times it can be shaped like a banana. Why's that?
0:25:26 > 0:25:29- I think we can solve that, don't you?- Yep.
0:25:29 > 0:25:32What do you know about the moon? Why does it light up?
0:25:32 > 0:25:35Is the sun reflecting on it?
0:25:35 > 0:25:39That's right. Just like us, the moon doesn't generate its own light,
0:25:39 > 0:25:41it gets it all from somewhere else.
0:25:41 > 0:25:43Do you know how old the moon is?
0:25:43 > 0:25:46- No.- It's really, really old.
0:25:46 > 0:25:52Almost as old as the Earth. Its 4.5 billion years old.
0:25:53 > 0:25:56It's not just the moon's age that's amazing.
0:25:56 > 0:25:59There are craters and plains on its surface.
0:25:59 > 0:26:02Just like here on Earth, there are mountains and valleys.
0:26:02 > 0:26:05Because there's no weather to wear down these features,
0:26:05 > 0:26:07you can see them really clearly.
0:26:07 > 0:26:09Even the footprints of astronauts
0:26:09 > 0:26:12who landed on the moon 40 years ago can still be seen.
0:26:12 > 0:26:15That's what's on the moon. Our challenge is to discover
0:26:15 > 0:26:19why it looks as if it has these different shapes
0:26:19 > 0:26:21when seen from Earth.
0:26:21 > 0:26:24I think we can do this with just a few things. I think we need
0:26:24 > 0:26:27a revolving chair and something to be the moon
0:26:27 > 0:26:31- and a bright light and a stick. Shall we go and find them?- Yep.
0:26:38 > 0:26:40Helen, I've got it.
0:26:57 > 0:26:59Right, I think we've got everything.
0:26:59 > 0:27:02I think you should be the Earth because you've got a blue top.
0:27:02 > 0:27:04What have you got there?
0:27:04 > 0:27:07I've got a polystyrene ball as our moon and a stick.
0:27:07 > 0:27:11So the moon can orbit you because you're holding it on a stick.
0:27:11 > 0:27:15Fabulous! And we've got a bright light in here
0:27:15 > 0:27:16to set up as our sun.
0:27:16 > 0:27:19Our universe has a bit too much light.
0:27:19 > 0:27:21Let's turn the lights off.
0:27:24 > 0:27:27Now the sun's lit, we're all ready to go.
0:27:27 > 0:27:29So that you can see the moon all the way around you,
0:27:29 > 0:27:33you need to be sitting on this spinning chair here.
0:27:33 > 0:27:35That's right. Hold the moon out in front of you.
0:27:35 > 0:27:38I'm going to spin you around
0:27:38 > 0:27:42so you can see what the moon looks like as it goes around you.
0:27:42 > 0:27:44What can you see?
0:27:44 > 0:27:47I can see one minute it's white and the next it's black
0:27:47 > 0:27:50and, in some shapes, it's like a banana.
0:27:50 > 0:27:53So, it's changing gradually as you go round
0:27:53 > 0:27:56and those are the phases of the moon.
0:27:56 > 0:28:00You have to make sure you're holding it high enough.
0:28:00 > 0:28:04If you don't you'll see that as you come round the back here,
0:28:04 > 0:28:07your shadow will cover the face of the moon,
0:28:07 > 0:28:09and that is what a lunar eclipse is.
0:28:09 > 0:28:13So, holding it down low there, can you see the lunar eclipse?
0:28:13 > 0:28:17- Yes.- The shadow of your head crossed over the moon.
0:28:17 > 0:28:20This lunar cycle starts with the new moon,
0:28:20 > 0:28:22when you can't see the moon at all.
0:28:22 > 0:28:24As the moon travels around the Earth,
0:28:24 > 0:28:27it takes 29.5 days to get back to where it started.
0:28:27 > 0:28:31On the way you can see all the phases of the moon.
0:28:31 > 0:28:33So, what do you think?
0:28:33 > 0:28:34We've cracked it, Helen, yes.
0:28:34 > 0:28:37We have. If you have a simple desk lamp,
0:28:37 > 0:28:40you can try this for yourself at home or at school.
0:28:52 > 0:28:57Subtitles by Red Bee Media Ltd
0:28:57 > 0:29:02E-mail subtitling@bbc.co.uk