Astronomy for 8-10 year olds – and adults too!
On Tuesday, History Future Now gave a talk to the local Cub Scout troop, where my two eldest children are members, about astronomy. The talk explained the origin of the universe, stars, our sun, planets and our bodies, plus the days of the week and astronomical distances of our solar system. Before I did the talk I wrote down some speaking notes to help me organise my thoughts. These are my notes. If you are a teacher this might be helpful.
One of them was something called spacetime. Space time is exactly what it sounds. It is space – the three dimensions of up down, sideways and forwards and backwards. Time is the movement in space. The other basics were gravity and the electromagnetic force. There were also some basic, fundamental, particles, some of which are called quarks. The quarks came together under the electromagnetic force and formed protons and electrons. The protons and electrons then formed together to form the first atom.
Does anybody here know what the first atom was? It is a special atom as it has only one proton and one electron. It is the lightest atom in the universe. It is called hydrogen. The universe continued to expand so fast that some scientists think that it expanded in the beginning at a speed that was faster than light. This expansion is called inflation and everything inflated at the same time. As the universe expanded something odd started to happen. Gravity started to kick in.
Who here knows what gravity is? Gravity is caused by mass. We think of weight as mass and for much of the time they are the same thing, though they are different. But the key thing about mass is that it pulls other things towards it. This pulling motion is gravity. Gravity is actually very very weak – you can lift your hand up and walk around – if gravity was very strong you would be squashed against the floor. But if you have lots of mass gravity can be very powerful. Gravity is what keeps you stuck to the surface of the Earth. If there was no gravity you would float off into space.
So what happened with the hydrogen atoms is that some of them started to clump together in huge clouds of gas- initially under electromagnetic forces which are quite strong – they are what keep your atoms in your bodies together – if you had no electromagnetic force your atoms would fall apart and you would end up spread all over the floor not as atoms, not as protons and electrons, but as gluons. As more of them clumped together they started to form mass. As the mass increased it attracted more hydrogen atoms until there was masses and masses of hydrogen all clumped together in a big ball.
And then something amazing happened. Do you know what that was?
The force of gravity became so strong that it started to bang the hydrogen atoms together. Some of those hydrogen got squeezed together until they fused together and in doing so the proton and the electron in the hydrogen fused with another proton and electron from another hydrogen atom to form a new atom, which had two protons and two electrons. As it did so it released a huge amount of energy and light as the electromagnetic force that had kept them apart was released. This additional heat energy excited other hydrogen atoms and with the gravity more and more hydrogen fused together until this giant ball of hydrogen gas turned into something that the universe had never seen before: a star, pumping out heat and light into the cold dark universe for the very first time.
So, we now have our first star. So if someone asks you what a star is you can say that it is a ball of gas, mainly hydrogen and helium that are fusing together under gravity to produce heat and light. But this is still near to the beginning of the story. These first stars were huge, 40 times bigger than our sun is today. They were so massive and so full of energy that they gave of a blue white light. Because they were so massive they had huge levels of gravity which forced huge quantities of hydrogen to fuse together creating helium.
But the force of gravity was so huge that some of the helium atoms started to crash into each other as well, creating a whole range of other atoms like oxygen – which is what we need to breathe – carbon – which is what forms the main building blocks of our bodies – neon – which is what many of our lights are made of – silicon – which is what glass is made out of and what computer chips are made out of – and eventually iron. At some point there is so much energy from all of these new atoms being created through nuclear fusion – the fusing of the nucleus of the atoms – that some of these stars collapse and in doing so blow up. This is called a supernova.
Now the explosions that occur are so bright and powerful that if you look up at the sky when one is taking place it can be brighter than all of the stars of an entire galaxy put together. And as they explode there is a massive and rapid fusion of all of the other atoms in the star so that even the really heavy atoms like lead and gold and uranium can be created. This ring is my wedding ring. It is made out of white gold. The only place that can produce this gold is a massive star that is in the process of blowing up. As it blew up the gold was created and billions of years later it ended up here, in my hand.
So we have been through the big bang, the creation of hydrogen and we have seen how the first stars were formed and how they blew up and in doing so spewed out all of the atoms that we know today all over their part of the galaxy. But we still have not seen any planets. So how did the first planets come about?
So imagine that you have had a star 40 times bigger than our sun blow up in our neighbourhood. All of the gases of hydrogen, helium, oxygen, carbon, silicon, iron, lead, gold, uranium etc are floating around. Some of them are close enough together that they attract each other using electromagnetic forces. Some of the atoms will hook up with other atoms of the same type. Others will hook up with atoms that are different, forming molecules. If you take two hydrogen atoms and an oxygen atom they form together to form a new thing called a molecule. Who knows what that molecule is called? Water.
A lot of the hydrogen atoms hook up together and because they are still the largest number of atoms in the area they gather together in a big ball of gas, but not as big a ball of gas as the original ball of hydrogen gas. Eventually, over 4.6 billion years ago there was enough hydrogen gas for their to be enough gravity for the hydrogen atoms to start to fuse together, to produce helium. This released heat and light, which fused more hydrogen atoms together, producing more helium light and energy. This continued and as with the first mega star, a new star was born: what we call our Sun. But there was still a lot of atoms that were floating around.
Those atoms started to clump and cluster together. They were not mainly made up of hydrogen and helium and so they could never become a star. The clumps got bigger and started to crash into each other. One of the mazing things about all of this rocky dust is that it started to spin around each other and as it span the ball started to get flatter and flatter until instead of being a big blob of gas it was all squished down into a flat disk with everything crashing into each other.
As some of the clumps got bigger their gravity got bigger, pulling in more clumps of rock and ice that crashed into the clumps which were now called planetoids – small planets. Further away from the Sun the left over lighter gases of hydrogen and helium formed around rocky core of planets just like the Earth. But because there was enough gas available these rocky planets used gravity to hoover up hydrogen, helium and other gases and became gas giants. If there had been more hydrogen available these gas giants would have had enough gravity to become stars. In many solar systems there are two stars, called binary stars. The biggest of these gas giants in our solar system we now call Jupiter, followed by Saturn with its rings, Uranus and Neptune.
By about 4.6 billion years ago, Mercury, which is the smallest planet closest to the Sun, Venus, which is almost exactly the same size as Earth, Earth and Mars existed. These are today the four rocky planets. But there was also another fifth planet, about the size of Mars, which we call Thea. Thea is really exciting because about 4.5 billion years ago Thea crashed into Earth. The whole planet turned into a squishy mush and billions of tonnes of rocks spewed out into space like some enormous volcano. Most of the rock fell back down to Earth but a big chunk went so far out into space that it started to lump together under its own gravity.
Who knows what we call that lump? It is called the Moon.
So we now have had an explanation as to how the universe was formed, how stars are formed, how our sun was formed, what planets are and how the Earth and the Moon were formed.
We also know that every single atom on our planet came from a dying star over 5 billion years ago. Atoms are almost impossible to destroy – unless you are in a star – and so the atoms that are on Earth are all at least 5 billion years old. Much of the hydrogen on Earth – which forms with oxygen to generate water (which is exactly why hydrogen is called hydrogen by the way – hydro means water and gen means to create) would have been released when the massive star exploded. Since the hydrogen would have been created at the beginning of the universe those hydrogen atoms in us are as old as the universe itself: 14.6 billion years old.
So when a plant’s roots take up water from the soil and its leaves take carbon dioxide from the air those atoms in the soil and the air become part of the plant. When you eat that plant the hydrated carbon -carbo hydrates- in the plant become part of you. Some of the carbon stays in your bodies and forms your skin, organs and muscles. Some of it is turned into energy when added to oxygen that you breathe in and when you breathe out the carbon and oxygen mixture, called carbon dioxide, goes back out into the atmosphere. Plants then take this carbon dioxide to form new carbo hydrates, which we then eat and the cycle continues.
The key point about this is that the actual atoms themselves are never destroyed. They just temporarily move from one thing to another – the soil, plants, animals and then the air.
We are going to go outside now, to look at the stars and also to look at Mars. The key thing to remember when you look at the stars is that they are a very long way away. The light from those stars travels at the speed of light, which is 300 ,000 kilometres every second. It takes 8 minutes and 19 seconds for the light of the Sun to reach Earth. That means that if the sun were to miraculously disappear, we would not see that it had gone for 8 minutes and 19 seconds. What we see is actually happening in the past. For the stars around us, such as Polaris the North Star, they are much further away – 435 light years in the case of Polaris. This means that the light we are seeing now left the star 435 light years ago. So when we look at the stars we are actually time travelling, looking back in history.The only planet that we will be able to see tonight is Mars. Does anybody know who Mars was? He was the Roman god of war. When you look at Mars you will see that it is slightly pink or red. Ancient people looked at this and saw this as a sign of blood and war. That is the reason he is linked to Mars.Ancient Greek astronomers were very sophisticated and their night skies were much better than we get here – there was no light pollution so they could see far more stars than we can. They noticed that some of the stars in the sky seemed to move around, whilst most of the stars stayed in the same place, but moved together, depending on the time of year. They called these stars the wandering stars. The Greek word for wandering is Planeetees. This is where our word “planets” comes from.The Greeks and the Romans could see Mars, Mercury, Jupiter, Venus and Saturn with their naked eyes. The other two bodies that moved around were the sun and the moon. How many moving things is that? Seven. Correct.
The ancient Germanic tribes living a few hundred years after Jesus also had Gods that were similar to the Roman gods. The German god of war was called Tiu, the equivalent of Mars. The German supreme God was called Woden. The god of thunder was called Thor, the equivalent of Jupiter. The wife of Odin, the chief god was called Frigga, the goddess of love, the equivalent of Venus.
And this is how we got our names of the week. Monday comes from Moons day. Tuesday from Tiu’s day. Wednesday comes from Woden’s Day. Thursday comes from Thor’s day. Friday comes from Friggas day. Saturday comes from the ancient greek god Saturn. Sunday comes from Sun’s day. So our days of the week are all named after the visible planets plus the sun and the moon.
Sum up. I hope that you found this interesting. You should now about the very origin of the universe, how the first atoms were formed, how the first stars were formed, how our sun and planets were formed and how you are really about 5 billion years old. You also know about where to find the North Star if you are lost, how the planets rotate, how they got their names and have seen Mars live in the sky.
As a result of this you now know more about Astronomy than practically every single adult that you will encounter!
Note to readers, while I was doing the talk I realised that I needed to keep things slightly more simple. Whilst I find quarks, gluons and plank’s constant fascinating, as they push the boundaries of what is known in physics (and dont get me started on dark energy and string theory!) there was perhaps a little more here than I could convey in a short period to adults, let alone children under 10. So I simplified. Nevertheless, they did get most of it, which shows that you don’t need to dumb things down too much for children.
I also ad libbed a bit – when we went outside I put the kids in a line acting as the planets and the two asteroid belts. This showed how close the rocky planets are to the Sun and how far away the gas giants were. I tried to simulate the Late Heavy Bombardment – the asteroids flying in under the gravity of Jupiter and Saturn into the inner solar system, but that ended up with a bunch of kids screaming across the field!
We were very lucky in seeing the International Space Station flying overhead. It was the brightest object in the sky. I strongly recommend the iPhone app Star Walk which allowed me to prepare for the talk by understanding what I would be able to see that night – and spotting the ISS when it came overhead.