The End of Night

80% of Europeans and Northern Americans now can't see the Milky Way. But does this matter?...
25 October 2016
Presented by Chris Smith, Kat Arney
Production by Graihagh Jackson.


Earth as seen at night from Space


Kat and Chris are turning the lights down low in search of darkness. 80% of Europeans and Northern Americans now can't see the Milky Way. But does this extra light pollution matter? It doesn't harm anyone, or does it? Plus in the news, with the US presidential elections fast approaching, we see what we can learn from animals when it comes to picking a leader. And, do you really lose most of your heat through your head?

In this episode

An egg

01:00 - Mice grown from stem cells

Scientists are hailing this annoucement as the 'tour de force' of embryology because it could pave the way for making artificial human eggs

Mice grown from stem cells
with Dusko Ilic, King's College London

In what embryologists everywhere are hailing as a scientific "tour de force", Artificial mouse eggs created from embryonic stem cellsJapanese researchers announced this week that they have successfully turned skin cells into eggs cells that are capable of being fertilised and giving rise to healthy young mice. Previously this had been achieved only by implanting cells into the ovaries of living animals. This new breakthrough, on the other hand, was achieved completely external to the body using a culture system. Dusko Ilic is a stem cell biologist at Kings College London. He wasn't involved in this piece of research but he took Chris Smith through what Katsuhiko Hayashi, the author of the new study, had done...

Dusko - This is a Japanese group that's worked a long time on this problem and the problem is how you can make eggs in a laboratory using stem cells.

Chris - Now why is that an intractable or long standing problem - why can't we do that?

Dusko - We don't know enough about it. To make eggs or sperm is probably one of the most complicated puzzles.

Chris - And what have this group actually done that means that we are a further step down the road?

Dusko - Several years ago they published their first report in which they used cells from a mouse tail. They fiddled with them in some way to revert them to embryonic state. 

And then they took those cells and put in mouse ovaries or mouse testes and those they put in the mouse ovaries after a month they become eggs. In this report they didn't use live animals; they just took the ovary, put it in a dish, put it together with the stem cells and they got eggs.

Chris - So just by taking a stem cell, by putting that in the right sort of melia - the right environment - an ovary or ovarian tissue, this is what then triggers those stem cells to then turn into egg-like cells again?

Dusko - Exactly, that is correct. So before they have to put in the ovary but now they figure out how to keep the tissue in dish and so in the right environment the cells know what to do.

Chris - What is the nature of the signal then or why do you think that putting these stem cells into the environment of cells that you would find in an ovary - why is that sufficient to make these stem cells then turn into some kind of egg-like cell?

Dusko - Because the ovary is not only made from eggs. There are different cell types and so they secrete different factors. They give signals and tell their neighbours what to do this is like a small tightknit environment. So like a village and they know what to do and influence each other.

Chris - And this influence is in the correct direction to make these stem cells turn into eggs. But are the eggs that are produced this way viable - in other words are they not just looking like eggs, can they behave like eggs and be fertilised by a sperm cell?

Dusko - In this report, they show that it is possible. They got from a certain percentage of eggs, they got live pups.

Chris - Right, and were those pups themselves potentially fertile or have they not done that experiment yet to show that it's not just one generation you can make, you are actually making fertile offspring?

Dusko - They didn't do this experiment yet. But the pups looked fine, they look healthy, and they showed that they can make from those eggs stem cell lines. Everything seems to be okay and in place.

Chris - And why is this important - why should we hail this as a breakthrough, if indeed we should?

Dusko - I think this should. There is two different, very important issues around this. So first this will help us to study and understand and find how to treat infertility cases in humans. Secondly, it may help to revive endangered animal species.

Chris - Because we could potentially take an adult cell from the animal we want to conserve and, even if it's male, you could, presumably, with the right culturing you could turn that into eggs cells from a male?

Dusko - Absolutely. So it has to be male because males have X and Y chromosomes (female and male chromosomes), so they can produce eggs and sperm. From a female you can get only eggs so that would be problem.

Chris - Well given this success story then what are the outstanding questions that you, as a specialist in this area, would like to see answered before you're comfortable that a) this is working the way they say it's working, and b) that we could consider extrapolating this onto say a human?

Dusko - I don't think that we should rush towards extrapolating to humans, so there is a lot of things to answer yet. First, if you're working with humans, how you can get human ovarian tissue. So we first have to go to the next step, which means culturing and understanding how to direct stem cells to make eggs or sperm without any other tissue present in the culture, and that would take probably years. Only after that can we see how it works - not only in mice maybe in other animals. So it will take years before we can even consider humans. 

06:27 - Tracking leukaemia-resistant cells

Leukaemia can become resistant to chemo but scientists have been watching cells in real time to work out how they become resistant...

Tracking leukaemia-resistant cells
with Cristina Lo Celso, Imperial College London

Leukaemia is a cancer of the blood and it's also the most common form of cancerEnvironments in bone marrow (blue, purple and green) as they are invaded by leukaemia cells (yellow). Image: Edwin Hawkins/Delfim Duarte in children. But like all cancers, leukaemic cells can become resistant to the chemotherapy used to control them. And scientists had thought that one of the ways that cells become resistant is by hiding themselves away in the recesses the the bone marrow and going into a state of suspended animation, placing them beyond the reach of a drug attack. Now Cristina Lo Celso has discovered that these cells are actually high active and mobile, as she explained to Kerstin Goepfrich, beginning with why chemotherapy doesn't always work...

Cristina - It actually works pretty well and it really gets rid of the bulk of leukaemia. We could see mice completely riddled with disease and in a few days of chemotherapy we could see just very, very few cells left. Now these very, very few cells left are really the problem be cause these are the cells that are able to regenerate the disease. And because these cells are chemo-resistant, it means that when a patient comes back to the clinic with a relapse it is much, much harder to treat.

Kerstin - Scientists had always thought that some leukaemia cells were resistant to chemo because they went into hiding, possibly seeking refuge from their destroyer in the bone marrow, but when Cristina started watching these cells she found quite the opposite...

Cristina - And that was that these cells don't hide and rather they run through the bone marrow, fairly constantly, so it really was very surprising and, especially, it is making us think about leukaemia in a very different way. And it is making us think about completely different approaches to tackle leukaemia survival.

Kerstin - So how did you find out that there are these runner cells that run really fast after you treated leukaemia with chemotherapy?

Cristina - What we did was to work with a specific type of microscopy that we have developed over the years that allows us to see live cells inside the marrow of live, anesthetised mice, and we have single cell resolution which is for live imaging through bone, it's really quite an achievement. And, because we can see single cells, we can really see those very, very few cells that are able to survive chemotherapy and not only can we see them but we can follow them over time. So sometimes we followed them for up 14 hours - that was a long, long night in the lab. But that really gave us an idea of how these cells behave over time.

Kerstin - But how about leukaemia in patients - how is that related to what happens in a human being?

Cristina - So this was a very important question for us and we wondered whether also the human cells would migrate - that they would move. So what we did was to work with some specific mutant mice, which are very heavily immunocompromised and we can inject human cells into these mice.  Because the mice don't have a good immune system they will not reject the human cells and the human cells can develop into the leukaemia in the same way as they develop in the patient. And so, in order to identify the human cells, we injected antibodies that recognised human cells as opposed to mice. And these antibodies were fluorescent so they would glow in the dark and they would tell us exactly where the human cells were, and we followed them over time and we saw that they were moving in the same way.

Kerstin - Sounds like it is time to run after the running cells. Do you have any idea how to do this?

Cristina - Absolutely! It's definitely time to run after the runners. So we know that there are a number of genes that are important in regulating the movement of cells and over the years cell biologists have developed a number of inhibitors, which means the number of drugs that can be used to interfere with these motors. And so what we are planning on doing now is to start off from already existing drugs and see if we can apply them to improve the treatment of leukaemia, at least in the murine models that we have available within the laboratory.

Kerstin - Sort of like sleeping pills for cancer cells?

Cristina - Yes, or making them lazy.

Kerstin - Wow that exciting! So what's next in the future?

Cristina - We have been able to collaborate with a number of clinicians and these are fantastic links that we hope we'll be able to do a lot more work together in the future. So we are definitely going to be busy in the next few years.


10:46 - Myth: We lose most heat from our heads

As winter approaches, Kat sees how we can keep warm by scrutinizing the science behind heat loss...

Myth: We lose most heat from our heads
with Kat Arney, Naked Scientist

This week Kat Arney's been getting hot over, rather than under, the collar...Teddy

Kat -   If you're listening to the Naked Scientists here in the UK, you've probably noticed that it's getting chillier. The nights are drawing in, the heating is going on, and you're busy raiding the wardrobe for gloves, scarves and  - of course - a nice warm hat. That's because we've all been told that we lose anywhere between half and 90 per cent of our body heat through our heads - depending who you listen to. Well, it turns out you shouldn't listen to anyone telling you that, because it simply isn't true.

It's hard to pin down exactly where this myth arose, but apparently the US Army Field Manual claims that 40 to 45 per cent of body heat is lost through the head. This is probably the result of early military experiments exposing people to very cold temperatures, while wearing various warm and cosy garments. As you might expect if you're all bundled up with your head exposed, you're going to lose most heat up top. But it does make sense. You'll only be warmer with a hat on, if the rest of you is also wrapped up. If you're wandering about in the buff with nothing but a bobble hat on, you can expect some funny looks - and also that the hat won't keep you warm.

So just how much heat is actually lost through the head, compared to the rest of the body? Well, for a start we need to think about the shape - and more specifically, surface area to volume ratio. We know from physics that smaller and thinner things with a high surface area to volume ratio will lose heat more quickly than bigger rounder things. The head is more or less spherical, which is a kind of shape that retains heat well (unlike thinner, flappier bits like hands and feet), and it only makes up around 7 per cent of the surface area of the body. And just to complicate the issue, people have different amounts of hair on their heads, which also acts as an insulator. To try and figure out how this all fits together, a Canadian researcher called Thea Pretorius started dunking unlucky volunteers in chilly pools, with or without their heads sticking out into warmer air. She discovered that dunking the head in the water only increased heat loss by about 10 per cent, suggesting that heat loss from the head is roughly proportional to the rate at which it's lost from other parts of the body.

But there's a twist. She's also found that the rate at which the core temperature cools down is similar if the whole body (minus the head) is cooled down, or if only the head is cooled. Intriguingly, cooling the body triggers a shivering reaction, which helps to warm you up, while cooling just the head doesn't. So, while it's not true that we lose more heat through our heads, having a cold head does cool down the rest of your body - in fact, a cold head increases core cooling by nearly 40 per cent. So, it's not so much keeping the heat in by wearing a hat on your head that keeps you toasty, as stopping the cold air getting to your head that makes a difference. What's more, making sure you keep your feet and hands warm with socks and gloves will definitely make a difference, as these are thinner body parts that will lose heat more rapidly than something solid and spherical like the head. So, as the temperature drops this winter, use science - rather than hearsay - to keep you warm and co

Tomatoes on the vine

14:25 - Why tomatoes are less tasty

Do you reckon tomatoes are becoming less tasty? Science is on your side...

Why tomatoes are less tasty
with Denise Tieman, University of Florida

Are you of the opinion that supermarket fruits and vegetables just don't taste as good as the fare you can pick up in the local grocers? If so, science is on your side, because new research out this week in PNAS has shown that refrigerating tomatoes reduces their flavour. Graihagh Jackson caught up with the study's author, Denise Tieman...

Denise - Well, I've always loved tomatoes; as a child they were my favourite food. I started doing research in plant science and I soon fell into a lab that worked on tomato flavour.

Graihagh - Because your latest paper is all about keeping tomatoes tasty, but I wonder was there a moment when you were like - tomatoes just aren't as tasty as they used to be?

Denise - Yes, that was some of our previous research, actually, so we know that modern tomatoes don't taste as good as some of the older varieties - what we call Heirloom varieties. A lot of our previous research was trying to define what really makes a tomato taste good and we tested many, many varieties of tomatoes. We had people taste them and then we looked at the biochemistry of those tomatoes and tried to figure out what really would be the recipe for a perfect tomato.

Graihagh - Uhmm, and what did you find - what is the perfect recipe?

Denise - Well, it's a complicated mix of many things. The main components of a tomato flavour are sugar, acids, and aroma compounds and we find we that we need a base of sugars and acids but the aroma compounds are what really make a tomato a tomato.

Graihagh - And it's the chilling of tomatoes that dampens these aromas and you've been looking at how this is happening.

Denise - Yes, so they're often chilled by the supermarkets, by the producers, and well, it's been known that chilling tomatoes makes them taste bad. So what we did we looked at what was actually happening inside the tomato after the chilling.

Graihagh - And what was happening?

Denise - Basically, the sugar and acids I was talking about, they are not changed with chilling but you lose a lot of the aroma compounds, so the tomato tastes bland, it doesn't have that tomato flavour. And so what we did was we looked at looked at what was actually happening at a genetic level and we found that with extensive chilling (about a week of chilling), the genes that make these aroma compounds are shut off.

Graihagh - These genes are responsible for making enzymes which, in turn, synthesise something called "volatile chemicals" - to you and me that's just tasty aromas. And when they're chilled the mechanism used by cells to control genes are turned off - in this case it seems forever!

Denise - They don't recover; they won't be turned back on again if you bring it back to room temperature.

Graihagh - There's a trade off then and I suppose many might choose to eat bland tomatoes and reduce food waste, especially given that most of us never normally eat them on their own. Which begs the question, does this finding really matter or is there something else going on here? For instance, could taste indicate the levels of nutrients within a tomato?

Denise - Well, that's another thing you know, and there's been some theories as far as that's concerned. A lot of these aroma compounds are actually kind of cues for different nutritional compounds. For instance, they come from carotenoids like lycopene and beta carotene that everybody tells us is good for us now, and some of them come from amino acids which we also need, and some of them of them come from lipids which we need. So a lot of them do seem to come from compounds that are actually very nutritious for us.

Graihagh - So it could be the case, and I suppose this might apply to other fruits as well that supermarkets are chilling?

Denise - Yes. Tomatoes are especially susceptible to chilling injury but other fruits and vegetables also are. Maybe not to quite the extent the way the lose so much flavour as tomatoes, but they do see the same thing happening with other fruits and vegetables.

Graihagh - Now that you sort of know on a genetic level what's going on, does that mean we can somehow use this and have tasty tomatoes that also last a sufficient amount of time?

Denise - Well that's what we hope. Now that we actually know what's happened, maybe we can find tomatoes, older varieties of tomatoes, that might be less susceptible to this chilling. And so, if we can find those, then we can go back and breed those traits into the modern tomatoes and, hopefully, prevent some of this loss of flavour with chilling.

A pigeon

18:47 - How democracy works in nature

With the US presidential elections fast approaching, we see what we can learn from animals when it comes to picking a leader...

How democracy works in nature
with Isobel Watts, Oxford University and Marta Manser, The University of Zurich

With the US presidential elections fast approaching, Connie Orbach sees what we can learn from animals when it comes to picking a leader...

I want to welcome you to the first Presidential debate. The participants tonight are Donald Trump and Hillary Clinton.

Connie - Choosing a leader can be a long and complicated affair with lots of stages, rules, and traditions...

The ninety minute debate is divided into six segments, each fifteen minutes long. We'll explore three topic areas tonight: achieving prosperity, America's direction, and securing America.

Connie - And it will often involve millions of people voting on mass based on information gleamed from months of campaigns. It's far from simple but humans are not the only animals to elect leaders. So when it comes to choosing positions of power, how do we match up? I asked Marta Manser from the University of Zurich to talk me through what the animals do.

Marta - Either it is being the strongest, being the most clever, having the best knowledge but usually it's not just the easy way to become the leader. But once you are the leader it might not take much to really suppress the others and to accept you as leader. Only if you show weaknesses the other co-members might try to overhaul you and take that position.

Connie - Any why is it that within these groups they're so happy to follow one leader - why would you make that decision?

Marta - It's probably the least energetic way. If I always have to make decisions and I have to convince the other individuals to follow that decision I'll to invest quite a lot of energy. And I think also in humans, that's probably very similar as long as that's a much easier way than to invest a lot of input time and energy, we are quite happy to follow other individuals.

Connie - Animals will often choose the easiest option. If they can use less energy following someone else than making their own decisions - well... all the better. It's definitely quicker, but not particularly rigorous. Us humans would surely know that the loudest in the group isn't necessarily the best.

Marta - If you have a group of humans, of individuals, and you tell them they should just try and be in the group but you tell one of those people specific information. For example, they should go to the location in the north, that individual should then, obviously, try to lead the rest of the group and try to make their way up north. And because that individual has a specific aim, it probably behaves quite dominant; it's very determined; it's going in that direction. The rest of the other people, they don't have a goal so they just follow the most obvious determined individual. And we find that in humans, we find that in meerkats, we find that in fish so that's a very common occurrence in the animal kingdom.

Connie - So when thinking about something like a Presidential election it might be the person that shouts loudest and longest might tempt us?

Marta - Yes, well exactly.I think in elections like that it's the emotions that count and then really, if you are the most convincing by being the loudest, by behaving very obvious, a lot of people might just follow that. They might not look at what the content of that person or they might just follow the obvious signs.

Connie - Oh dear. Maybe we're not as diligent as we thought. But no worries, if recent UK politics has taught us anything - when we're unhappy with our leader we can always attempt a coup.

Jeremy Corbin has lost the confidence of eight out of ten of Labour MPs and has been hit by as many as sixty resignations from his front bench team. He looks set to face a leadership challenge but Mr Corbin says he won't betray his supporters by resigning.

Connie - And we're not alone in that either as Oxford University's Isobel Watts found out -  pigeons will form a coup of their own...

Isobel - When a leader of a pigeon flock had incorrect information, instead of the information being passed straight down the hierarchy and, therefore, the whole flock taking and incorrect route which could be very detrimental, the hierarchy was actually able to reorganise itself and, therefore, the leader bird was no longer at the front. And, therefore, it's information was no longer as key to the flock's decision making and, therefore, actually the flock were able to fly the same route as they'd flown in training without taking this incorrect information. This was quite a key result and it showed that the hierarchy, although being very stable, it's actually a flexible system and they can use this flexibility in situations where the performance of the whole flock will suffer if it was inflexible.

Connie - Desperate times call for desperate measures when they know that their leader is possibly going to cause problems for everyone they can, let's say, relegate that leader and put them further down the pecking order. And how do you send a pigeon in the wrong direction in the first place?

Isobel - We use a process called "clock shifting." And clock shifting essentially jetlags birds, so it causes them to have a faulty compass. And what you can do is basically place birds in a light type room for a few days where you can turn the lights on and off at times shifted compared to real sunrise and sunset. Therefore, you can reset their internal body clocks to become shifted and this means once they're released they'll misinterpret the Sun's position by a predictable magnitude. So this means by just clock shifting the leaders we can create birds that have incorrect navigational information compared to the rest of the flock.

Connie - What if they don't want to lose their authority - what if your pigeon wants to remain a leader can they keep control of the pack?

Isobel - It's probably unlikely because I think all the other birds want to, for example, fly right and the leader wants to fly left, the leader doesn't have much choice. Because either it flies alone or it thinks it's more important to fly as a flock, which is often the case with pigeons, and therefore I'll just follow. But, we don't exactly know the mechanism behind when the leader loses its leadership because either the leader could choose not to lead, or the followers could choose not to follow.

Connie - Well there you have it, even in politics, we're not that special. But when choosing our next leaders, let's make a pact to contain our animal instincts and try to look a little deeper.


25:38 - Why we fear the dark

We face our fears and head into the dark to find out when it all began...

Why we fear the dark
with Professor Roger Ekirch, Virginia Tech

If you went outside right now, would you be able to see the Milky Way? The fact Darknessis that as more of us move to cities, light pollution is creeping into all of our lives. But how did we end up in a light-drenched world in the first place? Because of our fear of the dark, as Graihagh Jackson found out...

Graihagh - Are you afraid of the dark? I used to think that witches would come and bite my toes off it I lay on my belly and hung my feet over the edge of the bed. The real kicker was that this was the most comfortable way to sleep. But where does this fear of the dark come from?

Roger - It's impossible to say with any precision when our fear of the dark began, but certainly night was man's first necessary evil.

Graihagh - That's Roger Ekirch, historian from Virginia Tech. And you can see why it might be our first necessary evil...

Picture this... you're a caveman, it's nighttime and you're all tucked up with your furry skins ready for sleep, ahh. And then... what was that? You don't want to seem like a big jessie so you don't do anything - you just listen.

Jez is that a... that's it you're on high alert. Except it's pitch black, you can't see a thing so you listen all night long, praying for the Sun to come up, and that you won't get eaten alive.

Your fear, initially at least, was what was in the dark and then, eventually, your fear became of the dark itself. And this is an idea that Edmund Burke had...

Roger - The famous philosopher and political theorist in the eighteenth century was of the opinion that our fear was inherent.

Graihagh - But not all believe this to be true.

Roger - John Locke's explanation was that there was no such inherent fear. That, in fact, children were told ghost stories in order to get them to go to bed, in order to control them and, hence, this fear was instilled. More recently, psychologists have tried to bridge the gap. They have speculated that there was no innate fear of darkness at first but naturally, deprived of vision at a time when predators roamed free. Men and women, if they did not fear dark at the outset, they nonetheless quickly came to associate it with perils of all sorts, both real and imagined. So that by the time of ancient civilisations, virtually all associated darkness with demons, danger, and death.

Graihagh - And this makes sense, since being safely tucked up in bed in a house with locks and access to a light switch, we still fear the dark. Yet, instead of wolves, bears, and toe biting witches, it's criminals and car accidents. But, is there any evidence to suggest that there are more crashes and crooks at nighttime?

Roger - I think it's incontestable, although there are some fierce opponents of light pollution. The prime association being the International Dark Sky Association whose work I greatly admire. But to contend, as some member do, that there is no association between darkness and crime is poppycock in my opinion. The same with automobile accidents.

Graihagh - However, we have covered scientific research on the show that suggests precisely the opposite. Here's Rebecca Steinbeck from the London School of Hygiene and Tropical Medicine talking about her research she published last year. I played it to Roger too...

Rebecca - We invited every local authority in England and Wales to give us information on any changes that they had made to street lighting and, if they had made any changes to street lighting, what were the dates of those changes, and what were their locations. And then we were able to use data from the police on the locations and timings of road traffic casualties and crimes, and then we were able to model whether any changes in street lighting provision are associated with changes in road traffic casualties or crimes.

In the end, we were able to get data from sixty-two local authorities, which included over twenty-five thousand kilometres of road where there had been some form of street lighting change, and we found no evidence that these were associated with increases in road collisions or crimes.

Graihagh - Where's your evidence is what I'm trying to say when clearly this study suggests that, actually, there isn't more crime associated, or road collisions even, with darkness?

Roger - To that I would say, for that one study there are at least a five or ten that contradict it. I would also say that it's a matter of common sense whether you're driving a car down a dark road that you do not know, or in my case, walking in Richmond, Virginia, a city with a very high rate of crime, it can be very, very dangerous. I was reassured by the fact that there was any number of street lamps.

Graihagh - So in your opinion then Roger, our fear of the dark is still justified?

Roger - Yes, oh yes. To limit or, in some cases, entirely do away with street lamps would be, to my knowledge, the first example in human history whereby a widely used technology of proven merit had been rejected or constrained.

33:25 - Our night sky

As the sun sets in Cambridge, Chris Smith steps outside the studio with Paul Fellows to examine the state of our night sky...

Our night sky
with Paul Fellows, Chairman of the Cambridge Astronomical Assocaition

As the sun sets in Cambridge, Chris Smith steps outside the studio with Paul city skyline at nightFellows to examine the state of our night sky...

Paul - Well, sadly, we can't really see very much and it's getting worse here in Cambridge and elsewhere in the country. The amount of light scattered up from all these artificial lights, the street lights, the office lights, cars, everything, is just hitting the sky and bouncing back to us.

Chris - Can we actually see any stars?

Paul - At this precise moment, I've only just come outside, but no I can't. Even if I look where I know they ought to be...

Chris - There's one look, straight above your head.

Paul - Oh yes, you've spotted one before I did. That's Deneb in the constellation of Cygnus - well done!

Chris - Have you ever seen the Milky Way?

Paul - Oh yes, definitely! And we do see it on a good night here in Cambridge. Just right above your head at this time of year - near that star actually, it goes through the constellation of Cygnus.

Chris - But how old were you when you first saw it?

Paul - Oh I should think I was probably in my early teens; thirteen something like that when I first saw it. And I lived down in Portsmouth, which is a fairly big city and you could see it then because the skies were so much darker.

Chris - But not today?

Paul - Not today, and very rarely here in Cambridge these day, unfortunately.

Chris - I must admit, I probably had the same sort of epiphany that you did when you first saw it in your teens, but it took me until my late twenties. It wasn't until I went to Australia and was knocking around in the outback and staring up at this amazing sky and I suddenly realised what I'd been missing for almost the first three decades of my life.

Paul - Yes, I had the same idea. I went up to the Isle of Arran in Scotland, off the coast, away from all the lights and I was lost. I mean I know my way around the stars but there were so many and the Milky Way went right from one horizon above my head over down to the other side, and I was speechless.  

Chris - Now explain this to me. We're surrounded by street lights here and we can look at the impact in terms of objective measurement of that in a minute, but why should a bit of light here on the ground make a difference for our ability to see stars up there in the black void?

Paul - Well there are several reasons. Firstly, the light leaks from where it's supposed to go. It either goes directly straight up into the sky or it hits the ground and then bounces back up and it's scattered all over the place, and then it hits the dirt, and the dust, and the particles in the air and is bounced back to us again. So we see the sky as bright, it's not actually black.

And the second reason is to do with our eyes. Our eyes accommodate to the darkness by the pupil opening up and by the chemistry in the eye adapting to be more sensitive, and it takes about twenty minutes in full darkness for that to happen. But, if you don't have full darkness it'll never happen, your eyes, the pupils will stay small and you won't see any faint objects at all.

Chris - Well I've brought a newspaper out to see if I could read the newspaper. I thought I'd bring the Sun because that sounds suitably astronomical. So I can clearly here, apparently on this dark night, read every word on that page, certainly the headlines and even the smaller stuff. But I mean being able to read a newspaper under plain sight, that says quite a lot of light pollution doesn't it?

Paul - It does really and, of course, we're standing here and I can see you in colour and that means the colour cells in my eyes are perfectly happy and the rods that do the really sensitive work are shut down. So we've got no chance of seeing anything faint like the Milky Way in the amount of light we've got here.

Chris - How do we actually quantify the degree of the light pollution?

Paul - Okay well, there's a very useful scale called the John Bortle scale invented in 2001 and it runs from nine to one.  One is the best perfect conditions which we just don't ever get in England and nine is the centre of London or some big city like that where you can really only see the brightest objects like the planets, the moon and maybe one or two of the brightest stars.  Here in Cambridge we get about six which means we can occasionally see the Milky Way directly above our head and many hundreds of stars on a good night. If you go somewhere like the outback of Australia you might get down to a three or two and start to see other phenomenon, such as the zodiacal light which is actually dirt and dust in the plane solar system being illuminated by the Sun, and you see that just at the horizons coming up in the plane of where all the planets are.

Chris - Do you think in the grand scheme of things Paul this really matters?  As in we're not going not do astronomy we can just go somewhere like you're saying where it is dark and do the astronomy.  Does it really matter that we're polluting the night sky?

Paul - I think are a whole series of reasons, both astronomical and financial really. We're wasting energy by ruining the night sky with all this stray light if somebody's paying the electrical bill to do that.  But from an astronomical point of a view, it's a great way that kids get into science.  I run the cambridge young astronomers programme and we have kids from seven to eleven every Saturday once a month.  Some of them have gone onto get their PhDs now. It's a great of way of getting kids into science.

Chris - Is that what happened to you?

Paul - Absolutely, my first experience of looking at the night sky was with a small telescope my dad bought home and we pointed it up at the sky and said "what's that object there?" and "wow"  it was saturn with its rings.  So the next thing I did was build my only telescope.  Slightly bigger, actually bigger than I was at the time and that lead to a school prize and a trip to see Patrick Moore.  Tea and telescopes at his house with the great man himself.  

Chris - Patrick Moore invited you over?

Paul - Yes, I went round and he came bounding down the driveway in an old t-shirt and welcomed me and I spent hours there looking around all his telescopes and observatories that he had in his garden in Selsey down on the south coast and listening to him talk.  It was fantastic, I was completely hooked.

Chris - And I suppose in those days there wasn't too much light pollution was there?

Paul -   No, even there, he had a pretty good view.

Dead bird

39:44 - The dark side of light pollution

Having evolved to live in the dark, many animals are now exposed to light 24/7. What effect does this have on them?

The dark side of light pollution
with Bob Mizon, British Astronomical Association

There is an increasing body of evidence to suggest how light effects humans but what about animals? Kat Arney and Chris Smith explore the evidence...

Kat - Recently, an increasing body of research suggests that light is one of the key mechanisms involved in how our body clocks regulate. So having a light on signals to your body, WAKEY WAKEY and delays sleep hormones. Essentially, we're living in a permanent state of 'mini jet lag'

But it's not just any light, the colour of light is important. Norway's Mari Hysing, from Uni Health Research in Bergen studies the effect of blue light emitted from your computer screens, televisions and smartphones...

Mari - Many of these screens have quite bright light and some of the blue light might impact your hormone production or the sleep hormone, so it actually sets your clock off a little bit. So in the same sense that being outside in the morning helps your sleep, having very bright light in the evening will probably delay your sleep pattern making it harder for you to fall asleep at night.

Kat - With halogen street lamps increasingly being replaced by LED lights which emit a lot of blue light , this is a  cause for concern, especially if you happen to have one of these lights shining through your bedroom window this is because the blue light can disrupt your circadian rhythm, or body clock, as Dr John O'Neill, MRC Laboratory for Molecular Biology has argued on the show previously...

John - We know that circadian disruption as occurs during shift work for example, is really bad for you in the long terms so there's a very strong association with chronic diseases such as diabetes, neurodegenerative disorders...

Chris - Breast cancer...

John - Exactly, yes - a load of different cancer.

Chris - But this is in people, - people who can shut out the light with curtains blinds or by putting away their phone but what those who can't? I'm referring to nocturnal animals, who have spent millions of years evolving to live in the dark and are now confronted with light 24/7. What's the cost to them?

Kat - Bob Mizon is the coordinator of the British Astronomical Association's Commission for Dark Skies and he joins us from Bournemouth. Bob, we've heard about how light at night can be harmful for humans - is it the same for animals?

Bob - Verlin Klinkenberg in the National Geographic a few years ago said "that we have invaded the night as if it were an occupied country" when, in fact, nothing can be further from the truth. Every creature almost in the world has evolved for millions of years to have a day and a night and if we give them a day and a day they're certainly not going to thrive.

Kat - What sort of animals and how are they affected by this light at night?

Bob - Well most species in the world are nocturnal. It's a very good predator avoidance strategy, of course, being in the dark and the bats, moths and owls are the ones that come to mind because they're the ones we tend to see, Fish, for example, are pretty thrown by light on their water when it's supposed to be nighttime. There's a famous case about ten years ago in Stonehaven in Scotland when anglers were very put out that the fish were not rising to feed at night because the local tennis club was floodlighting their water, and the fish's feeding and foraging habits were completely disrupted. Perhaps they starved - I don't know.

Kat - I could see that would be a problem. One of the animals we do think about a lot of coming out at night is bats but here are impacts on birds as well as other flying species at night - what are some of the impacts on them?

Bob - Yes. I mean most birds - we know of a few nocturnal species but most birds are diurnal. When they migrate, they very often fly very long distances and this goes into the night. Some American and Canadian cities are now turning off lights in tall buildings because birds, for reasons still not clear, will fly straight into lit windows. It's the Fatal Light Awareness Programme, otherwise known as FLAP in Canada and America, which highlights this problem and they show on the internet where you can find pictures of literally thousands of birds that have died overnight hitting tall buildings. This is a problem indeed. Birds migrate partly by using the light cues of the stars and the moon and we really shouldn't try to overpower those cues by shining most unnecessary light. Canary Wharf at three o'clock in a morning - do all those lights really need to be on?

Kat - I think that is an issue. What sort of cost is it to the economy, and also to the environment, from keeping all these lights on all the time when maybe they don't need to be?

Bob - I've searched,  trawled through many a website trying to find the cost of light pollution and there are almost as many estimates as there are websites. But, let me give you one example: there is a website, I think it's from the Slovenian Dark Sky Association and they claim that Europe as a whole spends seven billion Euros - that's not million that's billion Euros - every year lighting up the night sky.

Kat - Wow! And presumably that's a huge amount of wasted carbon dioxide as well just going out?

Bob - It is. You know people say oh, astronomers moaning about light pollution. But it's everybody's problem because it's your council tax being thrown away. It's money and energy that we really can't afford.

Kat - So with the Commission for Dark Skies - what are you actually asking for? Should we just switch everything off and night and go back to completely living in the dark?

Bob - No, no no. Absolutely not, no. We're not crazy, we don't want people to live in medieval darkness. We want star quality lighting. We just want lights to shine where they're needed. I took a photo today of the latest new light on the wall of my community centre here in Dorset. It's a typical modern wall mounted LED floodlight; it cannot be pointed downward; it shines sideways into neighbouring houses; it shines into the night sky; it dazzles oncoming drivers and people walking to the centre. It's an anti-light, instead of revealing it conceals. This is absolutely poor lighting at it's very worst.

Kat - If you're campaigning for better lights and more sensible lighting, have you had any successes so far, are you actually getting this message through?

Bob - Yes, the Commission for Dark Skies has been in existence now for twenty-five years and we've had quite a lot of success talking to the highways agency for example. Eversince the mid-nineties, they will not put a road light in on a main road that shines up which is good. Nearly all are LED's and the only problem is they are too bright for the job and they're very blue and, as we've heard, blue is not good if live near a light.

Night Sky

46:51 - Living in the dark

There are many reasons to be reducing excess lighting. But is it feasible to roll out over large areas?

Living in the dark
with Graham Festenstein, Lewes Light Festival and Dan Oakley, South Downs National Park

There are many reasons to be reducing excess lighting. But is it feasible to Night Skyroll out over large areas? One community that reclaimed their night sky earlier this year is in South Downs and Graihagh Jackson went to investigate...

Graihagh - I've just arrived at the Lewes light festival and, of course, greeted by absolute pitch black. So much so that all my wires are tangled and I can't see what I'm doing. Good news though... it is a starry night and not a cloud in the sky, which hopefully means we should be able to do some good stargazing...

I was told there was a man in the moon - maybe he's hiding.

Graihagh - But, before I did any of that, I ran into Graham Festenstein

Graham - I'm a lighting designer and I'm also the festival director for Lewes Light. From my perspective our main thing is the glow worm so we've been working with a scientist from Sussex University who is researching into the impact of artificial light glow worms and that's inspired us to do this installation.

Graihagh - This is when we walked through there were a series of sort of hawthorne bushes and they've got lots of little green lights hanging from them.

Graham - That's right yes. And we've been working with Alan to look at developing these so they actually approximate glow worms. But what we've done is we've put the light installation at the bottom of the hill and the idea here is to get people who maybe don't come out and do this kind of thing to come along, look at the lights and then they can keep coming up and then they can come and look at the other activities - the astronomy, and the bats, and the moths, and just enjoy being out in the darkness.

Graihagh - It's funny because you never really think about going out to enjoy the darkness do you? But I decided to face my fear of witches biting my toes off and head into the night to see what I could see...

Everyone hear that... so that's us finding our dinner if we were a bat.

Graihagh - There were not bats sadly. What you can hear is actually is a demo. Further along though I finally found what I was after...

We're looking at the craters in the moon. Got a telescope looking up at the moon at the moment, we just had it on Andromeda galaxy.

Dan - The light festival's doing dark sky friendly installations and all the things here are fairly low powered and I think the Moon's putting out more light than the light festival at the moment. So right now it's fantastic - we've got lots of people looking through the telescope and enjoying the sights of the telescope at work.

Graihagh - Dan Oakley from the South Downs National Park and he calls it "the telescope of wow" because everyone who looks down it makes that noise of adoration. I joined the so-called "Moon queue" determined not to go "wow." But... the first thing out of my mouth... oh wow - classic - it's like the Moon's got acne. You definitely get a better idea of what Buzz Aldrin and everyone might have felt when they landed on the moon.

Dan - Yeah.

Graihagh - And I wasn't the only one enamoured...

It looked fascinating. It looked like a load of soap bubbles that have popped on a bar of soap. It was amazing.

Graihagh - I guess you've never seen the Moon in that way before?

No. No, absolutely not. It's not made of cheese, that's all I can say.

Graihagh - did you look as well?

I did and I thought it looked like cheese! Kind of Italian creamy gorgonzola cheese.

Graihagh - No wonder Wallace and Gromit wanted to go to the Moon.

A glass of red wine and I'll be quite happy now. Cheese and wine party.

Graihagh - Although the Moon illuminated the landscape around us, it was clear to me that this would have normally been pretty darn dark, and that's even though we're right on the cusp of the park where dark sky's reach towns and cities.

Behind me it was pitch black; not a fleck of light on the horizon. In front of me... well rays everywhere. But it was more than that - the cities glowed. They bathed the night sky with an aurora and this is what Dan Oakley kind of set out to change.

Dan - When we became a national park, part of that process was to consult with all the residents and talk about the qualities of the park, and one of those special qualities was tranquility and dark skies. And so when we looked at our management plan we noticed that our skies were getting brighter so we decided to do something about it and start this dark skies project.

Graihagh - So what classifies as a dark sky?

Dan - To be classified as a dark sky you need to really be able to see the Milky Way with the naked eye, and the other good thing to see as well is the Andromeda galaxy. If you can see those two things then they call that an intrinsic dark sky.

Graihagh - You took something like was it three thousand measurements over a few years, every night?

Dan - Almost, it was more like thirty thousand and the park is sixteen hundred square kilometres, plus the outside bits - that's quite a few nights. So we had a special sky quality monitor made up for us that could record at time intervals, so we just set it at five seconds and we just drove round the towns and recorded it over all those nights and all those cold mornings.

Graihagh - Are you naturally a night owl or was this a bit of a strain?

Dan - I thought I always was but I really do think I am now, so getting up in a morning is really difficult.

Graihagh - It wasn't just about taking measurements though and saying - Bob's your uncle, we qualify, wooh. Actually, Dan had to get the council on board to change their street lighting too.

Dan - Well they were coming to the end of all their streetlights. We all remember those horrible orange sodium lights and the were really optically inefficient because they threw a lot of their light upwards and it's that upward light that creates all the sky glow. So if you look at Lewes, you can see all that sky glow coming out now. When they came to do the streetlights it's then they put up more optically efficient streetlights which point the light downwards, and because that lights not going upwards and sideways it means the sky gets better. So a lot of the thanks goes to them really.

Graihagh - It's a shame because the reason why I came here tonight was to hopefully see the Milky Way with the naked eye for the first time but, alas, it's not my night to be I think. Because that's the idea of the dark sky's project is to be able to see the Milky Way with the naked eye, isn't it?

Dan - Yeah, absolutely. I mean tonight, unfortunately, the whim of the weather and the Moon but, when you can see the Milky Way, you know you're in a dark sky site and you'll just smile when you see it. And if you go to some really dark places you can start to make out some of the structure, some of the dust and that just elevates it even further. Then you get a real sense you're in a galaxy and again, that feels like you're looking at your house, your home in the Milky Way.

54:01 - Can light exert a force to move an object?

Why don't you get thrown backwards when you switch on your torch? Kerstin Göpfrich found out from Dr Anna Lombardi.

Can light exert a force to move an object?

Kerstin Geopfrich put this question to Dr Anna Lombardi from the University of Cambridge...

Kerstin - To shed light on this question I dug out my torch and made my way to the Nanophotonics Centre in Cambridge where I met with Dr Anna Lombardi.

Anna - can light exert a force to move a physical object? Anna - Yes, definitely. According the Newton's second law of motion, a force is the mass of an object times its acceleration. But light is weird, it travels at a constant speed, the speed of light and it never accelerates. In addition, light is made of photons which don't have any mass. The crucial point is that while light doesn't accelerate, and doesn't have mass, it does carry momentum and momentum, as a form of energy, can be transferred. By transferring their momentum, photons are able to exert a force on an object. Physicists refer to it as an optical force. The higher the frequency of the light, the larger its momentum and, therefore, a stronger force it can exert. This means that blue light will push you stronger than red light.

Kerstin - The theory tell us that light does have a little bit of a push but I certainly cannot feel it when I switch on my torch. What's the point of all the theory then?

Anna - While the push of light is so tiny that you don't feel it in everyday life, we can observe it at the nanoscale in the world of the infinitely small. Arthur Ashkin, a scientist working at the Bell Labs in the seventies demonstrated that nanometer and micron sized particles can be accelerated, trapped and manipulated by radiation pressure of a highly focused laser beam.

Nowadays, scientists use light quite literally like optical tweezers to manipulate objects from cells to single atoms

Kirsten - Does that mean that we just need a superpower torch to move the big stuff?

Anna - If as a light source we don't limit ourselves to a simple torch, but we consider the Sun, then the radiation pressure exerted is strong enough to push spacecrafts and even asteroids from their path.

Kirsten - So you'd better know the math when you plan your next mission to space. But Matt, I think we're safe to turn the torch back on. Thanks for your question and thank you Anna for the answer.


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