If the Earth

The cosmos is spinning, everything is in motion but for this walk we are going to line all the planets up along a single trail, but in reality the planets are usually much further away from each other. One could be around the back of the Sun whilst the next is in front, but lets not get hung up on this, instead lets start at the center, the Sun.

But before we do that we need to pull out our shrink machine and reduce it down to a manageable size.

So what if one step was equivalent to ten 1:10, in that one step yu would journey the distance it would normally take to do ten.

Now let's make that one step equal to one hundred, 1:100

Then just one stride could be as long as your whole street, or perhaps 1:1000 and you could be able to step the length of a whole road perhaps.

Maps do this really well, and you can walk with your fingers and eyes over massive distances in just a blink.

But lets up this a little more, what if with one step you could stride across an ocean or across the whole world? If one step was as wide as the world then how many steps would it take to walk to the moon?

But now lets go even further, what if our world was the size of just a pea and that in your single stride you could step over a thousand of them all side by side! If you could do this then how many steps would it be from the earth to Mars or Venus, or even the Sun?

Well to find out it's easiest to start at the center of our solar system with the Sun, if it's shining down on you now then imagine you were right there and you could shrink it down to the size of a beach ball or small Hoola hoop.

For the teachers this should be 1m diameter, you could even chalk it on the ground, or get your pupils to squeeze together and make a human Sun.

So lets get the Sun up to play, pop out the Hoola hoop and hang it from a tree so you can see it when you are a little way away.

This is the start of our Solar Explorer Expedition.

So we have shrunk the Sun down to the size of this Hoola hoop and we are going to venture across half of the solar system and discover the planets as close to an accurate scale as we can.

The Sun is not just set as a Hoola hoop as this is the easiest prop to hand, it is the right scale when the earth is shrunk down to the size of a pea.

But how far from here is the first planet, and which will that be?

Everyone should now stand how far away from the Sun the first planet should be.

Suggestion - Why don't you ask people to put themselves in a line so there is a definite person who is more right than the others.

Can you also choose from your planets which you think will be the first?

So our first planet is? (say out loud)

Here is a clue.

I am often the shiny metal in your thermometer?

Now walk the distance to the first planet, I am sure a few eyebrows will rise as you get a long way from the sun!

Mercury is 45m from the Sun

Mercury in ancient Greece was the God of eloquence, Poetry which is why it's craters are named after artists and authors. Craters are the dents in the skin of the planet where rocks have crashed over millions of years. If you were to throw a rock really hard into sand you would make a crater, the faster you throw then the bigger the crater, by looking at these you can work out lots especially about it's age.

It's smaller than the Earth in fact it's only a little bigger than our Moon. So pop a rice grain or bead in your hand. If the Earth was now the size of a pea then the grain of rice is about the right size for Mercury, check it against your chart. It should be 3.8mm in diameter.

Fact - Mercury is very close to the Sun and is seen as a shadow when it passes in front of it. This is called a transit and the next one is due 9th May 2016 though to see it you should pop a hole in a piece of card and look at the image it casts, if you see a tiny spec on the 9th of May then you are seeing Mercury.

Did you know that only two probes have visited Mercury as it is so close to the Sun. The first was in the 1970's, which flew by and mapped over half its surface. The other was launched in 2004 and took seven years to get there. After four years of capturing data it finally ran out of fuel and in April 2015 it smashed into the planets surface making it's own little crater amidst the millions of others.

Image captured by Hinode optical telescope which is a satellite orbiting the Earth in a way it can view the sun constantly. This means it goes over both poles, around and around but at no point is it in a position where the Earth is in the way.

Put your tiny planet Mercury on the ground as it's time to move on to our next planet, which, even though it's further from the Sun than Mercury, it is in fact hotter!

Suggestion - Ask your pupils to stand at what they think is the right distance, I bet they go a little further than before, but do they go far enough?

How far from the Sun do you think the second planet is?

So what's the next planet called?

Here's a clue, she is the God of love and also the name of a plant which catches and eats flies!

Count the steps and the distance gauge on your tablet, as it should be about 43m to our second planet.

Try and guess which of your spheres is the right one for this planet.
Venus is the second brightest object you see in the sky after the moon so it's likely that you have seen it, though you probably thought you were looking at a bright star. It is just about the same size as the earth, so get out a big fat pea or marble, this should measure 9.4mm in diameter to be precise.

Venus doesn't have any moons and is incredibly hot, so hot in fact it would melt the metal wings of an aeroplane! More than forty spacecraft have explored Venus and each one discovers something new about the planet though no one has been there in person, I wonder if anyone every will.

It's also the only planet that spins the other way, which means the sun rises in the west and sets in the east. The days don't go backwards though as that would be ridiculous!

A transit is the term used to describe one body passing in front of another, here the planet Venus passes in front of the Sun.

The next transit of Venus will not be for 100 years in 2117.

Now look back at the Sun and hold Venus in your hand and think about that just for a moment.

Now leave your little Venus on the ground and we shall go home next, for planet Earth is our next stop.

How far is Earth from here, show us how far you think it will be?

So which sphere is the correct on for Earth?

It should be 10 mm, now place your pea on the ground and then pull out your ruler and measure about 30 cm and place a grain of rice there.

What have you just done?

Can you see it in the sky?

You have just held the Moon in your hand!

A long time ago they thought the world was flat, and if you sailed too far you would fall off the edge. Centuries later, it was proved by observations of Moons around Jupiter that actually the Earth was round. But funnily enough even this is wrong, for it's more pear shaped than round and it bulges towards the middle.

The Earth has a lot of water on it as well which tends to swell and slosh about as it spins. For this reason, when they set the clocks for the millennium they had to add another second quite late on to make its rotation fit exactly to the time our clocks were showing. Clocks on earth are far too accurate compared with the celestial clock of the Earth itself.

Did you know that there are two asteroids which circle the Earth too, almost like second Moons. The largest is 5 km across which is about the diameter of a small city, they are in fact co-orbital satellites which means they actually circle the Sun just like the Earth does.

Factoid - the Sun is equivalent to 1.3 million Earths all squashed together. Have you a bag of peas, well you would need not just bags, and not just sacks of peas to get up to the volume required, you would need a whole lorry load of peas to be similar in mass to the Sun at this scale. But then you would need to boil them up and mash them together, and that's going to need a very big pan indeed.

The next planet was apparently named after a chocolate bar, or was it the other way around!!

Count the steps and the distance gauge on your tablet, it should be about 61 meters to our next planet and don't forget to leave the Earth and the Moon here.

Now hold out your hand with your 5mm bead, this is the actual size of Mars relative to the distance have been walking, tiny isn't it. (Actually it is closer to 5.3mm)

Mars is known as the harbinger of war, it sometimes looks red in the sky and often shines towards the end of the summer when harvests are ripening. That would be a terrible time to burn crops and starve your enemies out, but that's just what used to happen.

No body has ever set foot on Mars but loads of people are really keen to do so, in fact there is a competition running at the moment to choose a group to be the first resident's to live on the Red planet. If you could go would you? It would likely to be a one-way trip as the chances of getting back alive would be slim.

There is an atmosphere on Mars but it's incredibly thin, hardly anything at all and you wouldn't be able to breathe it. The highest volcano of all the planets including our own is on Mars and there have been nearly seventy missions to discover more about it but more than half of these failed. Some blew up on the launch pad, others crashed on the surface, another missed completely but stop a second and look back down the track you have walked to where you left the Earth.

Now consider that both Earth and Mars are constantly moving, with the Earth circling the Sun twice for one of Mars' orbits. So only every two years, (yes once around the Sun is a year) they will be this close together, which is not very close at all, the rest of the time they are either moving away from each other or moving towards each other at great speed.

It is quite understandable how difficult it is to actually get to another planet when you think of it like this; it is amazing we've managed any at all!

This image was taken by the robot called Curiosity as a 'Selfie' in the Yellowknife Bay area of Gale Crater on the surface of the Mars. You can see where it drilled some sample holes to see what Mars is made of.

Now leave your little planet here for our next stop is Ceres, and I am sure you are thinking I've never head of that one. Well lets go take a look, she is in a zone of rocks called The Asteroid Belt which I am sure you have heard of.

You are now standing in what is termed the Asteroid Belt, here there are tiny fragments right down to gravel sized pieces and smaller but some are big. The largest of these is called Ceres and is termed a Dwarf planet, but in astrological terms it's actually quite small, in fact it's less than a third the size of Earths Moon and smaller than Pluto which is also now termed a Dwarf planet.

Ceres was discovered in 1801 so we've known about it for quite a while and a NASA spacecraft, called Dawn was launched in 2007 and is now in perpetual orbit around Ceres. You may wonder how busy the asteroid belt is, well if you were to sit on Ceres and look for the next bit of rock you'd be hard pushed to do so, this is why probes sent out don't hit anything when they pass through.

Now next stop is the gas giant Jupiter, pick up your 112mm planet (might be the reel of Selotape!) and get hiking for our next stop is nearly the same distance again which you've just walked from the Sun!

But no running, as we can't travel faster than the speed of light!

Jupiter is one of the five planets visible with the naked eye and through binoculars you can see a few of it's moons quite easily, in fact it has 67 moons at the last count and it was once thought that these moons themselves had moons, but this is not the case.

The most notable moons of Jupiter are called Io, Europa, Ganymede, & Callisto, with Ganymede being the largest. In fact its bigger than Mercury which was the first planet we visited on our super solar tour. It's also the only Moon with a magnetosphere just like the Earth.

Pop out a tape measure and mark the four Galilean Moons of Jupiter.

Io 33cm from Jupiter with diameter 2.8mm (about the size of our Moon)
Europa 53cm from Jupiter with diameter 2.5mm (pictured)
Ganymede 84cm from Jupiter with diameter of 4.1mm (bigger than our Moon)
Callisto 148cm from Jupiter with a diameter of 3.7mm (same as Mercury our first stop)

So, on this walk we've journeyed 609m in real terms, which is 778 million km and if you were a single photon leaving the Sun and zooming at the speed of light it would take 45 minutes to get here. That's long enough to bake a lemon drizzle cake!

Now the next stop on our solar trek is almost double the distance again from the Sun, and is the gas giant with rings, do you know it's name?

You've got 491 metres to walk to work it out!

It will be our final stop as if we were to continue to the outer edges beyond the dwarf planets of Pluto, Eris, Makemake and Haumea we would need to walk about five and a half km from here, which is just over three miles. That's a long way to go to carry a grain of sand or a pinhead although it is thought there could be up to ten thousand dwarf planets hiding out there!

Saturn has only 62 moons at last count, it also has rings, which are very wide and in places incredibly narrow, so narrow in fact you could pass through from one side of the rings to the other in just five juicy steps. That's just 5m wide, why don't you measure it on the ground and see if you can do it in less.

Hint for adults – if you've forgotten your tape measure then take five big strides and that's about it!

The size of Saturn at this scale is 95mm, which is a third bigger than a tennis ball. Jupiter's is bigger by a small margin but it's rings extend out much further although Jupiter has a ring system too it's not as extensive as Saturn's. The diameter including the rings is 221mm at this scale, which is easiest to illustrate by cutting a hole in a paper plate for your planet to sit in.

This image is of Saturn's Moon Mimas and shows loads of craters plus one really big one. Some people say that it looks like the Death Star from Star Wars, but photographs of the crater didn't exist until three years after the film came out.

So this is a good place to end our trail at planet Saturn, and before you head back have a little look at the other spheres you have yet to distribute further along the trail. They are so small and the space's between are quite extraordinary.

Also have you noticed that each planet is roughly twice the distance from the Sun as the previous one? This makes our next planet Uranus another 1.1km from here; the Sun itself is 1.1km away. A photon travelling at the speed of light would take an hour and a twenty minutes or so to arrive here and then the same again to arrive at Uranus. That's nearly a whole school morning at the speed of light!

After Uranus is Neptune, the former is roughly the size of a Ping Pong or Squash ball and the latter slightly smaller, more like a big marble (40mm and 35mm). Neptune is four hours out from the Sun at light speed or a slow walk at this scale. It's really cold which you would be if you were that far from your heater, both these planets are often referred to as the ice giants.

After Uranus and Neptune we have dwarf planets Pluto, Haumea, Makemake and Eris being the furthest from the Sun. Makemake is the only one of these which doesn't have any Moons itself.

So that's our solar system shrunk down to pocket size (though I challenge anyone to try and put the Sun in your pocket at this scale!) But the rest of the planets you could do.

But the thing, which always strikes me, is that there is a lot of nothing between all the planets.

I suppose this is why it's called space, because that's generally what's there!

Enjoy your walk back to Earth.