We discovered them about a hundred years ago, but I can’t imagine we won’t have discovered something better than radio waves in another four hundred years. So earth might be sending radio waves out for only 500 years in total. For a planet almost 5 billion years old means that there is only a one in a ten million chance of anyone listening in with a radio telescope of catching us at the right moment in our evolution. So that’s the last number we need - the number of years a civilisation sends radio signals into space.

“So what’s the answer? How many planets in the galaxy have intelligent life?”

At least one.

35 Planets of the solar system: little ones.


“So Albert, what's next on this tour of the solar system?”

Well, we're just passing through the asteroid fields between Jupiter and the next planet we'll come to which is Mars.

“So where are all the asteroids? On Star Wars when they went into an asteroid field they were dipping and diving to miss them.”

One day I'll have to see this Star Wars film you keep talking about, but I'm not sure it gives you a very accurate picture of the universe. There are certainly plenty of asteroids it's just that space is very big.

“So how many asteroids are out here?”

I just looked up the number, by last month they had found 378,546 asteroids but they are finding thousands more every month so there may be a million or more out there. The biggest Ceres is much smaller than the earth's moon, around 600 miles across, and that single one contains a third of all the rock and ice in the asteroid belt.

“Is Ceres another Greek or Roman God?”

Well guessed, Ceres is the Roman God of agriculture. Ceres was the first asteroid they found and initially astronomers thought it was a new planet, until they started finding more and more of them in the same area. For a while they kept giving them names of minor Gods and Goddesses, like Pallas, Juno and Vesta.

“Then what happened?”

They were finding so many that they were running out of names, so the the discoverers starting naming them after their country, family members and even pets.
Now there are so many that most have only numbers or a scientific code. Have a look at THIS PAGE to see if anyone you know has an asteroid named after them .

“OK Albert, back in a minute...”

“Back again. I don't believe it. There are asteroids called Smiley, Doctor Watson and Asterix! Isaac Newton has his own one, but I'm afraid there's no Einstein just an Albert.”

Well that will do fine, I've a big crater on the moon named after me so that's enough for any man.

“Guess what asteroid number 9007 is called?”

I'm not sure I know that, sorry.

“James Bond!”

Why?

“James Bond? Double 'O' 7, get it?”

Is this a Star Wars thing again?

“No he's a secret agent, but he is in films too. Once this trip is over Albert I need to sit you down and show you all the great films you missed since you died. Oh, was that an asteroid we just went past?”

That was a fairly typical small lumpy looking asteroid yes.

“Hmm, not very exciting are they? How about getting onto the next proper planet?”

Not so fast young man, patience. They may be small but asteroids can have much more effect on the Earth than any of the monster planets we were talking about earlier.

“Such as?”

Such as killing half the living creatures on Earth for a start.

“Now you're the one talking about the nonsense from films.”

No, it really happened. That's how the dinosaurs died off and it wasn't just them. In the seas even more species were lost than on land.

“This sounds like science fiction.”

No just science but like a lot of science it started with a crazy idea that people found hard to believe. Luis Alvarez and his son Walter Alvarez made the suggestion in 1980 that an asteroid about 6 miles across crashed into the Earth 65 million years ago and caused the dinosaurs to die out.

“How could they possibly prove that?”

All over the world in rocks that were 65 million years old they found a thin layer of clay that had lots of an element called Iridium.

“What does that prove?”

Well there is very little Iridium in most rocks but there is a lot of Iridium in asteroids and meteorites.

“OK, but where's the big hole?”

They found a crater in Mexico that is now buried under the sea that dates from just the right time. They've even found a few other possible craters from around the same time in India and in the North Sea near England, so something big could have broken up and landed in several pieces.

“Oh, so people think it really happened. It's not just a crazy idea?”

No, now it's a considered the most likely reason for how the dinosaurs died out.

“Could it happen again?”

Yes it could. There was an even bigger extinction 251 million years ago when 90% of sea and 70% of land species died out. That might have been an asteroid too. The Earth is always being hit by small things, a hundred tons arrives from space every day but most are tiny particles or dust that burn up as they arrive. But there are bigger asteroids that come near the Earth and could possibly hit it one day.

“Any time soon?”

There seems to be no immediate risk, but I read that a few years ago it was predicted an asteroid called 1997 XF11 might hit Earth October 26 2028. Don't panic, they made a slight error in their calculations so it will miss by a safe margin.

“Phew. So the Earth is safe for now.”

Well...an asteroid called Apophis, the Egyptian god of evil and destruction who lives in the darkness might just cause a problem. On April 13, 2036 this asteroid has 0.0022% chance of hitting the Earth or a 1 in 45,000 chance, but on the bright side there is a 99.9978% chance the asteroid it will just miss us.

“Apophis destroying the Earth. That's straight out of Stargate, now I know you are joking.”

No, straight out of Nasa. Take a look for yourself. http://neo.jpl.nasa.gov/risk/a99942.html

“So we may have to work out how to blow up asteroids after all to save the world.”

We might.

“Is that 13th of April in 20..whatever a Friday by any chance?”

No I think it's a Sunday.

“Phew.”

Now it's time to get some practice blowing up a few asteroids. Have a go at this great game I found.

Wait for sounds to load and then Click on Asteroid field then press S to start

Instructions
S	Start Game	P	Pause Game
Cursor Left	Rotate Left	Cursor Down	Reverse Thrust
Cursor Right	Rotate Right	Cursor Up	Forward Thrust
Spacebar	Fire Cannon	H	Hyperspace Jump
M	Toggle Sound	D	Toggle Graphics Detail

Our journey will almost be over before the human race arrives at a reasonably accurate answer to the question of how old the sun is and where it gets its energy from. As stars are pretty much the most important things out here in space, it makes sense to explain how stars really work now rather than wait for humanity to work it out over the next few thousand years. The source of energy that makes the sun shine and the stars shine is a continuous nuclear bomb, an H-bomb or Hydrogen bomb. The surface of a star like the sun is around 6,000 ^oC but the core is nearer 15 million ^oC which for those of you more familiar with gas ovens is about gas mark 79,000.

"So long can this H-bomb burn for?"

Stars, in fact the whole universe, are made up of mostly of this material called hydrogen, and stars are huge so they can shine for billions of years. The sun has been shining for 4.5 billion years and can keep going for another 4 billion years. This energy comes from the process of nuclear fusion, where atoms are combined to create completely different atoms and in the process release colossal amounts of energy.

"I’m not sure I really understand what an atom is"

An atom? Atoms are what everything is made from. They are the building blocks of the universe, sort of like LEGO. Atoms, like LEGO, come in different shapes but atoms are really minute, so small you can't see them even with a microscope. This atom idea dates back almost to the start of our journey. Democritus of Abdera was an ancient Greek philosopher from around 400 BC and developed the first well thought out concept of the universe being made up of atoms. As a young man he travelled to Athens to meet Anaxagoras, the hot rock man, but was very upset when Anaxagoras refused to meet him. Democritus has the consolation that his own ideas have lasted far longer than the famous older philosopher who snubbed him. At one time everyone thought that atoms were unchangeable. You could break things down into the individual atoms but they thought that you couldn't turn one atom into another or break up an atom. There aren’t even that many types of atoms, only 92 different types exist naturally.

"You're trying to tell me that everything is made up from just 92 types of atoms?"

I am indeed and each of these different types of atom is called an element. They vary from the very smallest which is hydrogen to the biggest which is uranium. Even more surprising is that despite all these different types of atoms or elements, nearly three quarters of the whole universe is made up of hydrogen atoms. So most of the universe is made out of a single type of atomic LEGO brick.

There's a diagram called the Periodic Table, first developed by the Russian Dmitri Ivanovich Mendeleev in 1869 that lists out all the atoms/elements in terms of size. Hydrogen is the smallest, followed by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon…

“OK, I believe you. I don’t think I’ll be able to remember all 92 anyway.”

Well like I always say, imagination is more important than knowledge. As long as you can imagine a universe made from 92 different elements that is more important than remembering all their names. That’s what reference books are for, to hold all the boring facts you can’t remember or don’t really need to remember.

You don’t even need lots of different types of atoms to make complicated things. Human bodies are amongst the most complicated things in the universe, but incredibly humans and most living things are basically made up of just six elements; carbon, nitrogen, oxygen, hydrogen, calcium and phosphorus. These six types make up 99% of your atoms with the last 1% a range of other rarer atoms.

"That's not many types of building blocks; LEGO would be dull with only six types of blocks"Well when you start combining atoms or LEGO blocks there’s an almost infinite range of things that can be built. Take just six LEGO blocks of the same size with 2 by 4 little studs, all the same shape and colour, and you could make 102,981,500 different shapes. How fast could you click together 6 LEGO blocks?“Oh, two or three seconds I suppose.”

Well at that speed it would take you almost ten years to try all possible ways of clicking together just six LEGO blocks. So it’s no wonder that you can build an entire universe out of 92 different types of atoms.

“It must take a while to make a universe then?”

Oh, it does. This one is almost fourteen billion years old after all. .

"So is light made of atoms?"

No, although all physical things in the universe from stars to humans are made from atoms we’re not. We photons are different; we're a form of energy and exist just as we are. Like heat, we can affect atoms but aren't made of atoms. Take a fire. The smoke coming out of a fire contains atoms but the light and heat you feel from a fire is energy and, in fact, is a type of photon like us. But let’s finish off atoms first. Atoms were initially thought to be the smallest division of matter but, in fact, atoms themselves are made of particles. An atom is made up of a nucleus which defines what sort of atom it is and a cloud of particles called electrons that spin around the nucleus. The electrons have a negative electrical charge and are the particles that help to carry an electrical current through a wire. The electrons are also the parts of atoms that can link atoms together to make different combinations of atoms that are called molecules. Your body is held together by these interactions of electrons which are called, reasonably enough, chemical bonds.

"Hold on Albert, let me get this staight. Atoms join together to make molecules."

That's right.

"Are humans just big molecules then?"

Well humans are made up of thousands of different types of molecules and each of those molecules is made up of atoms. By combining different atoms in different shapes the same six atoms (with a few extras thrown in here or there) can make up all the important molecules in a human like DNA and proteins. Have you heard of DNA?

"Like in Jurassic park?"

Fascinating thought recreating dinosaurs. I just read about it while I was waiting for you to join me. I'll explain all that a bit later but let's sort out the basics first. Now, where was I? Oh, yes, the glue between atoms is made up of electrons which make up chemical bonds. These bonds are where two atoms both think an electron belongs to them and hold onto them tightly.

"So if both atoms are holding onto the same electrons then the two atoms stick together, like a pair of kids 'sharing' the same toy."

Well sort of, but it does get a little more complicated from here. There are a few more names to remember about how atoms are put together, but it's worth the effort because you need these facts to know how stars shine. The nucleus is made up of two types of particles called protons and neutrons. The number of protons in a nucleus defines what element it is and neutrons somehow help to hold everything together. Remember the periodic table I just told you about?

"Hydrogen, helium, lithium and all that?"

Precisely. Well one proton means that atom is hydrogen, two protons means helium, three makes lithium and so on.

"And it doesn't matter how many electrons or neutrons, two protons in an atom is always helium?"

That's right. The protons determine the essence of what an atom is. The neutrons and electrons are important but not as critical. Take a dog. If it looses a leg and some of its fur it's still a dog inside and will still look like a dog even if it is three legged and a bit mangy looking. Legs and fur are like neutrons and electrons, important pieces of whole picture but the essential doginess is set by the protons.

As well as defining the type of atom, protons also carry a positive charge that helps to hold the fast moving electrons in their orbits. Remember the electrons have a negative charge and like the opposite ends of two magnets, positive and negative attract each other. So protons help the atom to hold onto its electrons. The simplest element hydrogen has a nucleus of one proton and one electron whizzing around it. Oxygen has eight protons, usually eight neutrons and usually eight electrons. A really heavy atom like Uranium-238 has 92 protons and 146 neutrons. Still with me?

"I think so."

There are a few more names worth hearing about, mainly because the names are so weird. You'll also impress people if you know this last piece of the atomic jigsaw puzzle. Even protons, neutrons and electrons are not the end of the story. They are made up of smaller particles called quarks. Scientists have made up some curious names for these quarks like ‘up’, ‘down, ‘strange’, ‘charmed’, ‘truth’ and ‘beauty’. In an attempt to be taken more seriously some scientists have renamed truth and beauty to top and bottom, but I rather like the original names. A proton contains two up quarks and a down quark whereas a neutron has one up and two down quarks. Naturally they are all held together with particles called gluons.

"You're making this up as you go along."

Honestly that's what they are called. But don't worry about quarks, unless you just like the names, we can still explain most of the universe without thinking about quarks. All the same it's nice to know that everyone of you has inner beauty, truth and charm no matter how well it's hidden at times.

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 at 9am on Sunday October 26th 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.

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’.

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 1954 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.