How Stars Shine

Let’s imagine what was going on back on Earth as we are leaving Deneb. For the first few thousand years of our journey the human race had little inkling that stars and the sun were even related. As to how the sun managed to shine so brightly they were equally misguided. As is often the case, this didn't seem to stop some people having strong views about what it wasn't. In 500 B.C. a Greek gentleman called Anaxagoras of Clazomenae almost got sentenced to death for the heresy of saying that he thought the sun was a very large, very hot lump of rock. He escaped punishment with the help of a powerful friend Pericles, but was forced to leave Athens in disgrace. Anaxagoras also calculated that the sun was 35 miles across and about the same distance from Greece as New York would be when someone finally got around to stealing it from the American Indians. His maths was fine but he thought the Earth was flat, which was why his calculations were a bit off.

"A bit tough almost being stoned to death just for getting the answer wrong, isn’t it?"

It wasn't being wrong that was the problem. It would have been just as bad for him if he'd got the right answer.

"How come?"

By suggesting his own ideas he was saying that everyone else was wrong. The real problem was that back in 400 BC the Sun was thought of as a God. So it's no wonder the rulers of ancient Athens didn't like the hot rock idea.

"So when did they work out what stars really were?"

Well they didn't really make any more progress in next two thousand years either. In the middle of 1800's a German gentleman called Julius Robert von Mayer tried to work out how long the Sun had been shining for. He worked out that without some source of energy it could only shine for around 5,000 years. This was based on getting a rock as hot as a rock can get and seeing how long it would take to cool to its temperature today. This time scale would at least have pleased an Irishman, a Mr James Ussher who ended up becoming Archbishop of Armagh, Primate of All Ireland, and Vice-Chancellor of Trinity College in Dublin. Despite all these jobs he spent a lot of time working out how long all the events and stories in the Bible would have taken and worked out the family tree of all the people in the Bible, back to Adam and Eve. He calculated from this that the world began on October 23rd 4004 B.C. He also worked out that Adam and Eve were driven from Paradise on Monday 10 November 4004 BC so it was a short two week holiday in the Garden of Eden.

For scientists back in the 1800's, a 5,000 year old sun was a rather alarming concept because it didn't give them enough time for their theories on geology and evolution to work. The new sciences of geology and evolution assumed that the shaping of the Earth and the creatures that walked on it was a very slow process. Charles Darwin, the man who invented the theory of evolution, was saying that life must have been for around for much longer for humans to have evolved from fish and tadpoles. In Darwin's first edition of On the Origin of the Species by Natural Selection, published in 1859, he made a calculation that the Earth and therefore the sun must be at least 300 million years old. It was either abandon the hot stone theory, or invent a whole new theory to explain where dinosaur fossils came from. In 1857, just before Darwin published his famous Origin of Species, Philip Gosse had another suggestion for dinosaurs. In his book Omphalos, Gosse claimed that God had planted fossils and other evidence of a non-existent past during the six days of Creation to test our faith. After all if the world was created yesterday complete with your memories, photo albums and tree rings how could you tell?

“You couldn’t I suppose.”

Exactly, but believing something that is unprovable isn’t science it’s faith. As scientists were becoming quite attached to Darwin's theory, they kept looking for ways to explain how the sun could have been burning for millions rather than thousands of years.

"So why aren't stars just like big burning fires?"

Well stars are hot and yellow like fire so thinking that the sun is a large burning lump would make sense. But...if the sun were burning like a coal fire it would last barely a thousand years before ending up as cooling embers. Never mind the fact that fires need air to burn and there is no air in space. A thousand years isn't long enough for history books let alone evolution. There was another theory at this time that was a bit more promising. This new idea was that the gravitational contraction of the sun would generate a lot of heat. This new idea came from Hermann von Helmholtz in 1854 and developed by Sir William Thomson. He became Lord Kelvin after this and I’ve a few entertaining stories about him I’ll tell you one day. Anyway Sir William Thomson as he then was calculated this was enough to give the Earth about 30 million years of free lighting.

"But how does gravity make things hot?"

By squeezing things closer together. When you put your finger over the end of a bicycle pump and pump away. The pump gets hot because when air or anything else for that matter is squeezed together or compressed it gets hotter. So the gravity of the sun squeezing together the inner layers would heat up the sun from the inside. This was a nice idea but it still wasn't a long enough time. Evolution needed hundreds of millions of years not just 30 million years, after all the dinosaurs died out 60 million years ago. But this didn't worry Sir William Thomson at all as he didn't believe in Darwin's theory of evolution anyway.

Leaving Albert's Star

Shall we start on our way?

“Why not.”

Why not, indeed. One of the best reasons for doing anything. So here we are at one of my favourite stars, Deneb. Stars are grouped together into what are called constellations and named after animals or mythical beings. Our star is part of the constellation Cygnus or the Swan. For most constellations the pattern of the stars doesn't really look like anything, let alone an animal. On a clear summer night our constellation is almost overhead, a huge majestic cross with outstretched arms. So it really does look like a swan in full flight.

“Does it?”

Well sort of like a swan, in the same way a stick drawing of a man looks like a man. Our star Deneb is the tail of the Swan and a huge distance from the Earth, 18,970,843,745,070,000 miles to be precise. It’s hard to imagine what that kind of distance really means but in car journey terms it would take over thirty billion years at a steady 70 miles an hour.

"Wait a minute, how can we get there in 3000 years if it would take thirty billion years to drive there?"

But we’re not going to drive, we’re going to fly through space. We are going to cover such a huge a distance in such a short time because we're travelling at the speed of light. We are light particles or photons now. Not just any light, the very best type of light – starlight. So travelling at light speed comes naturally to us. Even though this sounds like a long journey, it’s really a fairly short stroll through this galaxy, the Milky Way, a journey of a mere 3,227 light years in a galaxy that is over 70,000 light years across.

“Is a light year the same as a normal year?”

Even though it sounds like it ought to measure time, a light year is a measure of distance rather than time and is how far light can travel in a year. At 186,000 miles a second and with over 31,000,000 seconds a year that makes a distance of almost 6,000,000,000,000 miles or six trillion miles. To give you some idea how far a light year really is, the Earth’s moon is only a light second away. Now think how much longer a year is than a second.

Deneb, is one of the largest, brightest stars in the whole galaxy, that’s why I like it. It's 160,000 times brighter than the sun and much bigger. So big that in the Earth's solar system it would stretch all the way from the Sun to the Earth. If the Earth were going around Deneb rather than the Sun it wouldn't be floating in space but skating along the star's surface and cooked to a temperature of over 8,000 ^oC. Deneb only looks like a very normal star because it is so far away. If Deneb was as close as Earth as the nearest star, Proxima Centauri which is only 4 light years away, it would be bright enough to cast shadows at night and be visible day and night.

“So what would the sun look like from Deneb?”

Not very impressive. If you looked in the direction of the sun from Deneb with just a pair of eyes you wouldn’t even be able to see it. You’d need a very powerful telescope to make it out as a faint very ordinary looking star. If today you had a powerful enough telescope to see what was happening on earth all the way from Deneb what would you see?

“Is that possible?”

No, but try and imagine it.

“OK, well you’d see all the people doing what people do these days I suppose.”

Not at all, you’d see what people were doing three thousand years ago. If light takes that long to travel from Deneb to the Earth, it will take that long to go the other way. So the light from earth reaching your telescope would be three thousand years out of date. If little green men from the Deneb solar system pointed a huge telescope towards the Earth today they would see the Earth around the time of the Trojan horse.

“So is all starlight old?”

When you look up at a star filled night the light reaching your eyes has been traveling for tens, hundreds or even thousands of years. For each star the light you are seeing started its journey at some moment in history. Imagine there are stars whose light started towards Earth before the time of the ancient Greeks and Romans and light that has been traveling since before Columbus first set foot in America. As you look up there is starlight that left its star in the year you were born and light from galaxies that has been traveling for millions of years.

“I thought that people claim to tell the future from looking at the stars?”

Oh astrologers think that but when you look at the stars you are looking at the past not the future. Don’t confuse astrology with astronomy. Astrology is merely the art of telling people what they want to hear. Astronomy is the science of working out what stars are and what is happening out here in the universe.

"So why is our star called Deneb?"

Well not all stars have names but where there is one it usually comes from the ancient Arabic astronomers. The Romans named most of the planets after their own Gods but didn't seem to bother so much with the stars. After the Greeks and Roman empires died out and before Europe emerged from the dark ages, the Arabic universities in places like Basra in modern day Iraq became home to the world’s best mathematicians and astronomers.

“Iraq?”

Oh, Iraq was part of a great civilisation back then with the most important universities before any had even started in Europe. Have you ever wondered why all of Europe speaks different languages but write numbers down in the same way?

“No, but now you mention it that’s an amazing thought.”

Well, that because the way we all write numbers comes from one place, Arabic mathematicians in places like Iraq. Every country seems to have one golden era, sadly they never last for ever. Iraq, Egypt, Greece, Italy have had their day in the sun. I don’t suppose today’s great countries will be so great in another thousand years. That thought should make the leaders of today’s superpowers a little more humble, but I suppose you don’t get to lead a superpower by being humble. Anyway our star Deneb got its name from the great Arabic astronomers, though over the centuries it changed slightly - its name comes from the Arabic Al Dhanab al Dajajah that means 'the tail of the hen'.

"I thought our constellation was a swan."

Well things have gotten a bit mixed up over time, but all things considered we've been quite lucky with our names. Take Betelgeuse, the big red star in the constellation Orion, the Hunter. This star started with the Arabic name Yad al-Jauza, or Hand of Orion. It somehow ended up as Bait al-Jauzah which over time became Betelgeuse which apparently means the ‘Armpit of the Mighty One’.

The Beginning, 1223 BC

Earth Time............................1223 BC

Time to Go............................3229 years

Distance Still to Travel.....18,982,601,317,890,000 miles

Have you ever looked into a mirror and seen beyond your reflection? You have to stop worrying if your hair is right or your nose is too wide. Seeing beyond your face can be hard but not impossible if you try. You know what? The more beautiful or handsome you are the more you worry about how you look. The cleverer you are, the more you think about other things and like my grandmother always said, clever people age well. Over a hundred years ago I was bored and looking into a mirror. Did I look handsome? Sadly not, but I was more interested in the light leaving my face, hitting the mirror and coming back to my eye. What would it be like to be that beam of light? What would the world, the universe look like if I could travel that fast? Strange questions for a sixteen year old perhaps, but often all you have to do is ask yourself the right question. That one question changed my life, because I stuck with it until I had an answer. It took me half my life, but it was worth it. I spent all that time answering the question mathematically, but now I want to take this trip on a beam of light just for fun.

“Excuse me, who exactly are you?”

Albert, Albert Einstein of course. Well, I certainly remember being Albert Einstein and then back in April 1955 it all went blank. According to the history books I’ve seen since that’s when I died. Then suddenly I’m back here imagining things all over again. It seems someone has recreated a version of me inside this computer, which is fantastic as so many wonderful things have been discovered while I’ve been gone. How many people get a second chance like that? I get to do all things I never did first time around , like this trip.

“So who am I then?”

Well you have just joined me in a thought experiment, so I could have imagined you or I suppose you could be imagining me. This is my favourite type of experiment because you can go faster and further by thinking than by doing. Whoever we really are, for now we are light particles that have just left a star around three thousand years ago. As we set off over a thousand years before the birth of Christ, the Trojan War is raging and the classical Greek and Roman empires haven't even started yet. During our journey these great civilisations will have come and gone. By the end of our travels when we reach the planet Earth the human race will have progressed, if that is the right word, to a society that has put dogs into orbit, men on the moon and where everyone is looking for fifteen minutes of fame on television. But not all humans are that bad, a lot of good and clever people will have lived and died by the time this journey is over. During the next three thousand years while I’m enjoying the view I’ll tell you all about the important things that have been discovered about science and space. Most of it was discovered by other people but I can explain about my ideas on Relativity and a few other things that I discovered as well if you like. Did you know I invented a new type of refrigerator back in 1926 with my friend Leo Szilard?

“No, sorry.”

Not many people do, but we heard of a family who had died when the chemicals in their refrigerator leaked, all because of a faulty pump. So we developed a fridge that didn’t need a pump and had no moving parts. We got a bit carried away though and over seven years developed three new types of fridge and got forty five patents. Mind you I wish I’d invented the microwave oven, far more impressive.