to the museum of the history of science and technology is now. saying that kool-aid has been studying no papers work including his explanation for why the camera obscura makes an image that's upside down. he's well regarded as as the first science is to correctly explain the camera obscura talk me through how this works if you press the button there. this is a primary light source and this is the object lighted by it to slight the light has to go into the box it through despair hope you see here and if you look at from here. you will see that the this. is it is upside down. yes because the light from the top passes in the hole. and they cross over cross over because light takes the shortest way and it travels in straight lines

and this was something that he was able to show improve the fact that light travels in straight lines was known before him but he heard the first time proved it mathematically. it will hate them skitz album a novel is often cited alongside newton's principia mathematica as one of the greatest textbooks in physics ever written let in translations of it influence such men as division chief galileo descartes among others such as his fame today he is commemorated on the back of an iraqi ten thousand d.n.r. banknote he's probably most famous for being the man who explained how the vision works. until then the excepted view had been that of the ancient greeks men like plato in

euclid who argued that the way we see objects is by shining light out of our eyes on to them. it will hate him we knew of this view from arabic translations of greek texts but he challenged it arguing instead correctly that the way we see is by light entering our eyes from outside are the reflecting off objects or directly from numinous bodies like candles or the sun. what was most impressive about them is that he combined theory and experiments so not only would he devise careful experiments to demonstrate particular ideas like light travelling . straight line he also put mathematical flesh to these ideas he math i'm a times whole fields of science. professor stephen sweeney is a colleague of mine at the university of sorry he works at the cutting edge of

laser physics today in the medieval world there's one star in particular that i'm passionate about it no hate them and he wrote a book of optics a thousand years ago in which he was doing all those sorts of things that you sociate with with experiments with like today so reflection and refraction of light even down to designing experiments with camera obscura is to prove that like travels in straight lines but those aspects of understanding the properties of the key to modern science technology actually but perhaps the idea that light travels in a straight line is one of the most important ones and it's one that we really now make use of in technology and science and actually we've got a nice example of that here that i can show you today just based on research we're doing right now we're going to be using a laser and we need to wear these just to protect our eyes for the experiment. ok so what we've got now is there's a beam of light and a visible beam of light shining a nice straight line from this laser down to this detector the other end now if i

put this card in the way you can see that there's a nice spot nice red spot when i take that away the lights travelling through and it's hitting this piece of material here that's got a photovoltaic cell so you've heard about solar cells for flecked and sunlight this is a particular type of photovoltaic cell for collecting laser light and it's actually then driving this little motor so it's just little fancy five like that again it stops if i pull that away you can see the fan starts again ok so it's another way of transmitting energy essentially so not using electricity but using light itself is the medium and what sort of applications might this device this set up one of the key projects that we're interested in at the moment is transmitting energy from space because in the infrared we can actually get straight through the atmosphere without losing energy we use a system like this in space we could transmit solar power twenty four hours a day anywhere on the planet that we needed this has huge implications the world

over in terms of producing power we wouldn't need pylons and power lines yet power could be delivered to remote areas or disaster zones and this technology also has implications for the internet we obviously use the internet for data transmission but use infrared light actually but if we also put in some so high powered components that we can also deliver the energies we can actually deliver the power signal for the internet as well and this this light you see infrared so if i put my hand there i don't see it i can sort of i imagining i can feel what you're probably imagining it because i don't although it's infrared light it's not quite far enough into the infrared to be measured as heat the reason we use infrared light is purely because it's a better way of transmitting that light through the atmosphere and actually more than ninety nine percent of the energy can transfer through the air now in the real application that we would. this fall we've actually been even further in for it laser and that would allow us to not have to wear these safety goggles so it's what

we call the nice safe way for a sort of wondering what your haitham would think of doing experiments with candles and pinhole cameras. but he wouldn't even be able to imagine a world a thousand years later i think it's come a long way but ultimately we using exactly the same principles but he was thinking about. today we understand the physics of how light behaves but back in hate can stay this wasn't a total obvious his book changed everything and he's regarded by many as being the father of modern optics in fact i'll go further than that and say he was the greatest physicist in the two thousand year span between archimedes and isaac newton.

so many cities around the world today spectacularly by light it seems the applications of optics are reverie where you have a look at this beautiful fountain behind me it looks as though the colored beams of light are bending round following the path of the water however that's an optical illusion lights in fact a shining up from the base of the fountain and then reflecting off the water droplets into our eyes like always travels in straight lines however there is a way that light can be made to bend. if i shine this laser pen through this glass of water if you look carefully you can see the beam of light. as it enters the glass in the water this is something that every physicist knows as snell's law refraction but it was known many centuries earlier. let me show you this rather remarkable diagram it's

from a text that was discovered only twenty years ago partly in tehran and partly in damascus it's by a little known scholar by the name of it been sad and it describes snell's law of refraction beautifully let me explain this line represents the boundary between air and water if a beam of light enters the water at an angle it will refract bends towards the vertical this angle is larger than this one or draw a circle around it the ancient greeks understood that this angle of incidence the angle that the beam enters through the air is no larger than the angle of refraction in the water but they knew that the ratio of the two angles remains constant if you doubled this angle that angle doubles the way they described it was

in terms of the ratio of these two parts of the circles perimeter that was wrong what i've been so help understood was that it was in fact the ratio of two straight lines he said that this chord divided by this chord is always a constant number this is the correct way we understand it today now europeans argue about whether it was snell or descartes who should be given credit for them over a fraction in fact it was discovered by even six hundred fifteen years earlier so really it should be known as it been so hands nor a fraction. and another little known scholar from the golden age fascinates me is a man called it been who in the eleventh century came up with one of the earliest

estimates of the heights of the atmosphere there he'd worked out that after the sun sets the last remaining daylight's comes from light reflected off the upper edges of the atmosphere he figured out that this would take place when the sun was nineteen degrees below the horizon. imagine that i'm standing on the surface of the earth at this point a. the sun has gone nineteen degrees below the horizon above me is the atmosphere and i can see the last light of the day reflected from the top of the atmosphere at be. we can draw this triangle to the center of the earth that. knowing the size of the earth calculated by the astronomers of baghdad in the ninth century they've been marked was able to use geometry to work out that the atmosphere was about eighty kilometers high that's not bad for almost

a thousand years ago. throughout the golden age. and many other scholars wrote detail texts on optics but none were so comprehensive and influential as if no haitham ski tarpon menarche . at the same money a library in istanbul professor. shows me an ancient copy of it no haitham scrape work. other. than the book of optics. of course this isn't in the original copy this was written in the mid fifties century. mohammad who founded the ultimate empire is written for his library.

filmy what's amazing is that we all around the world we talk about newton as being the father of optics and yet here we are a thousand years ago seven hundred years before newton and his away diagram this is there's a there's a convex lens and there's a focal point and there's all the brain lines and power lines in the angles of refraction here it is a thousand years ago. optics are all around us from the glasses all contact lenses you wear to the screen you're watching me on right now to the particles of light produced in the synchrotron everything we know about thought six today is built upon the work of scholars like insect had been logged and the father of modern optics if no hate who first opened

our eyes to the science of life. next time i'll be taking a look at modern day astronomy in that occasion and exploring the contribution made to these fields by the scientists of the golden age that's where his genius comes in because this diagram it's also a couple simplified a lot of that complicated math we see the role they played in the evolution of astronomy we still have had to develop an area of mathematics called spherical geometry which was exceptionally advanced four thousand years ago and we reveal how scholars from the summit world consolidated and refined the astronomy of the civilizations and came up with ideas that have influenced the story of the right through to the present day copernicus this day to these medieval astronomers from the golden age.

in the next episode of science in a golden age i'll be exploring the contributions made by scholars during the medieval islamic period in the field of astronomy. copernicus is this day to these medieval astronomers from the golden age. that's trillions in many ways with the computers of the day you can use it to find the time you could navigate science in a golden age with german. a controversial politician elected to the highest office in latin america's biggest

country. brazil is about to inaugurate its new president jaya polson are. join us live from the capital brasilia on inauguration day. they wanted forty three billion pounds worth of weaponry that was six billion pounds in commission. there is no hope of ending off because there's always a small cobble of people for war really really good business. in essence we in the united states have privatized the ultimate public function war shadow on al-jazeera. short films of hope and inspiration. a series of short personal

stories that highlight the human triumph against the odds. al-jazeera selects. syria's military says it's entered the city of man beach after a call for help from kurdish fighters but u.s. forces are disputing the claim.

and have sake of this is al jazeera live from doha also coming up. i'll talk about a chorus girl louder for sudan's president to step down on the tenth day of protests. new shoes a boat builder two could be biased. to me is just a nonsense a president on the defensive but there's mounting anger at a decision to cancel voting in three cities in the democratic republic of congo. and fuel for thought we look at how germany's pushing for green cards. allow the syrian army says it has entered the northern city of mann bridge after a request from syrian kurds for protection but u.s. forces on the ground say they've seen no indication that claim is true the kurdish armed group the white b.g. says it feared an attack from turkey following the u.s.

decision to withdraw all its troops russia has welcomed the move but syrian opposition sources have also told i understand there's no sign of government forces in the city the syrian army made the announcement on state television but it hasn't broadcast any images of its forces in man beach. based on the full commitment of the army and the armed forces to assume national responsibility for the imposition of the state sovereignty over every inch of the territories of the syrian arab republic and in response to the appeal of the people in. the general command of the army and the armed forces announces the entry of units of the syrian arab army to be and raising the flag of the syrian arab republic the armed forces guarantee the full security of all syrians and others who are present in the region or turkey's president says the situation in men remains unclear. we know that syria is making psychological effects

a psychological ect we know there is a situation with their own flag has been hoisted but there is nothing confirmed serious yet i spoke with my friends with intelligent sitra about an hour ago and there is nothing certain and the spying meant are just updating in our what's happened in syria recently on december nineteenth donald trump ignored pentagon advice and announced the withdrawal of you all u.s. troops in syria about two thousand have been trained fighters against arsenal some arab nations have normalized relations with syria both the u.a.e. and behind reopened empress embassies in damascus sudan's president became the first arab leader to visit since the war began eight years ago and turkey's military forces have massed on the border with syria president richard type one promising to wipe out the remains of i saw in syria and russia hosted

a delegation of the syrian democratic forces which help the u.s. in the fight against eyesore. oh how would i know is life for a sin to pay in turkey on the border with syria so mohammed conflicting reports then as to where exactly the syrian syrian army is in man because what more can you tell us well hossam it seems everyone is in agreement that the city and forces are actually involved in the mumbai residents of the city who we spoke to the u.s. forces who are patrolling the outskirts of the city and potholes down the global on the ice in court as well as the turkish forces on the turkish government the syrian rebels all of them on they're all syrian government troops in mumbled to despite the claim. on the military formed on the turkish side thinks of

more very quickly we've seen reports of government troops crossing the border from get up loose as well as the free syrian army fighters who are allied to the talkie also inching closer away from the front lines near mint bridge towards the city saying they're preparing for the offensive but again nothing is for sure yet we do not know whether these offensive is going to take place after all because of the thing depends on. a sincere a delegation that is led by the foreign minister of turkey is going to have with russian officials in will school on saturday and headed as far as that that requests to the requests from the. syrian kurdish y p

g for to the syrian army to take over manage fearing an attack from turkey that all seemed to happen quite quickly didn't it. yes indeed and the term that the kurds are feeling abundant they're feeling pushed to the wall the announcement by the president to withdraw syrian for the u.s. forces in syria completely only got them all but also has created a lot of concern about their future in early on this year when the turkish forces have launched an attack on the region of free and they had decided to fight for about a couple of months before they decided to leave and go to places that one of the control of u.s. full says of now they feel they don't have

a lot and according to kurdish leaders they feel that it's much easier for them to negotiate with the government of bashar al assad who as you've been saying their husband resurging and recent weeks. for example risk for all smoked by turkish forces on the city of mumbai which foreign mohammed thanks for that mohammed our live for scene gaziantep near turkey's border with syria that thousands of anti-government protesters in sudan have returned to the streets they gathered in the capital hard to know as well as in the north and what met danny in the south early and nine leaders were detained them a strange things began over rising living costs there since why didn't call for an end to president obama say to you who. he will morgan has the latest from car too. it's another day of anti-government protests and that indicates that people are not

willing to listen to the cover messages the government has been saying that they're going to try to interviews new comic reforms and they're going to try to improve the situation and they said that they want people to be a little bit more tolerant a little bit more patient but today's protests in several cities in khartoum and several other parts of the country is showing that people don't want to listen to the government and the people are keen to continue to protest and demand the president step down after twenty nine years of rule now the government have also been accused of using brutal force by the u.n. and other foreign governments they've been responding with live ammunition and tear gas to disperse protesters who've been marching every single day for the past nine days and it's only protesting that people have been. carrying out to try to voice their demands of the president step down some of them have also been on strike they've been doctors in that area who announced that they're going to go on strike until the government step down and we've also seen some journalists as well and solidarity of journalists who were harassed and arrested during while covering the protests they said that they're also going to go to national strike against the government until the government's at a time so this is becoming more and more of

a national movement now when the protest started it was more of a people and the people who are protesting described it as a revolution but over the past few days we've seen opposition figures voicing their support and lending their support to the movements of protests around the country they're saying that the people who are protesting have legitimate reasons to protest they have legitimate reasons to voice their concerns and demand that the government leave and try to bring in a new interim government to power until elections are held but then the government has been responding by basically arresting of opposition figures nine opposition figures were arrested last night to basically scare of protesters after they've demanded their support to protesters for today's protests so the government has arrested several opposite opposition figures but that has not stopped people from protesting today and there are concerns that these protests will continue and that the police and and the military who have been deployed around the country will also use live ammunition to try to disperse the protesters and that would put their lives at risk. morgan in khartoum when the democratic republic of congo

a general strike is being held in the opposition areas excluded from sunday's presidential election workers was walked out in the northeastern city of beni and police fired tear gas in goma one officer was injured there a shortage of voting machines in the capital kinshasa is concerning election organize our correspondent michael ware joins us now from kinshasa so mark on what's been the response to the call for a general strike. in the sense is the fairly what had started as a peaceful shutdown erupted into street protests and police there we've heard have been struggling to control those protesters the protesters surrounded the private residence of the police commander and. then proceeded to the residence of the mayor police were able to disperse the protesters from there with live bullets and tear

gas but then they proceeded back to hospital and since then i was pleased to still struggling to break up groups of protesters throughout the city in some other recent sounds and one of the town the office of the ruling party was burned and in the city of goma people have been trying to protest the police broke up those process with tear gas and live footage as well but all these people are angry because they see the electoral commission decision to not allow the presidential elections to go ahead on sunday in those three opposition strongholds bias the electoral commission said it's because of a bug or outbreak because of conflicts but opposition supporters believe them and there's a widespread mistrust generally for the electoral commission here in congo as it stands we interviewed president joseph kabila and one of the things i asked him about them was that perception that the electoral commission is biased let's hear what he had to say. this issue issues about the electoral commission be

biased. to me is just a nonsense the most important thing we should or understand and retain is that it is an independent electoral commission these are congress elections and that's what everybody has to understand and there are. issues that have risen once in a while and we've been able to do them as a nation we don't want anybody to judge us and that apart from the congress people so malcolm can this election really be seen as free and fair then with the possibility of more than a million votes being discounted. a lot of skepticism from opposition supporters anyway and now that been pushed to another level by the recent decision that the electric.