As winter creeps over the Northern hemisphere, many of us will be turning time backwards by an hour in aid of daylight saving time. But why do we do this? In this episode, we weigh up whether there's really a robust rationale for changing the clocks depending on the time of year, hearing from scientists and historians...
In this episode
00:42 - Earth's day and night cycle
Earth's day and night cycle
Matt Bothwell, University of Cambridge
It’s that time of year when many of us in the northern hemisphere prepare to scurry around our homes setting our non-digital clocks back one hour to reflect the end of daylight saving time…and the arrival of winter. Changing the clocks in this way, as we’ll find out a bit later, is a relatively new phenomenon and one that is dictated by national governments. Night and day, however, is a consequence of the Earth’s tilt on its axis. But how exactly does it work? Chris Smith popped along to visit Dr Matt Bothwell, public astronomer at the University of Cambridge’s Institute of Astronomy...
Matt - Our planet is spinning. We spin once every 24 hours, the sun shines on one side of the planet and that gets daytime, the night side of the planet on the other side from the sun is night time. And then, every 24 hours, the earth rotates and we swap places.
Chris - So if you are in a big country and you are over on the East side of that country, the sun is rising for you earlier than people on the other side of that country?
Matt - Exactly, yeah. If you imagine being in New York or something on the East coast of America, you are going to spin around onto the daylight side of the planet and the people in New York will see sunrise even when people in California are still firmly in the nighttime side of the planet.
Chris - What about going up and down the planet? If you are on the equator, how does the time the sun rises and sets differ compared with, say, if you're up in London?
Matt - So that gets a bit more complicated, and it depends on the time of year. It's all down to this fact that the earth is a bit wonky. If the Earth was a perfectly sensible planet, straight up in our solar system, there would be no variation. Days and nights would have equal lengths at all times of year on all parts of the planet. But the earth is wonky: it's knocked on its side by this angle of about 23 degrees, which gives us all kinds of interesting effects, one of which is the different day and night times as you go up and down the planet. So, in summertime, the days are longer and in winter the days are shorter.
Chris - What does that do to the timing of sunrise and why does the tilt of the planet affect that timing?
Matt - So, in summertime, which is when we are tilted towards the sun, the sun rises earlier and earlier. I think the easiest way to think about it is, if you just imagine a sphere on its side, a bit wonky, being illuminated by light from the side that's tilting towards the light, well there is more of the light on that side of the planet. And so you spin round and you'll hit that light side just a little bit earlier than you would otherwise.
Chris - And the same's going to go for the setting of the sun, so it's going to set earlier as well. And that means you're going to get a shorter day in winter and a longer day during the summer?
Matt - Yes, exactly. In the summer, that light patch is bigger, and so sunrise is earlier and sunset is later. And then, in the winter, you have the complete opposite effect, there's much less of the illumination. So the sunrise is later and sunset is earlier. And then we have those horrible short days in the winter where the sun never rises and then when you leave work at 5:00 PM it's nice and dark.
Chris - What about the extreme, which is when you go into the far North or the far South and there is this phenomenon of the land of the midnight sun.
Matt - So, at the very extreme, so either the North Pole or the South Pole, let's imagine the North Pole, for example. In summertime, the North Pole is tilted towards the sun and because of the Earth's tilt, during one entire rotation, you stay entirely within the illuminated bit. So the sun never goes below the horizon. So yes, in the summertime in the North it is the land of the midnight sun where you will just look up and see the sun doing a little circle around the sky and never actually dipping below the horizon. And the opposite is true in the winter. I'm part of the South Pole telescope collaboration. I've never actually been down to the South Pole, but my collaborators go down for the winter and you see the last sunset in the winter and then you are in for about four months of darkness until you see the sunrise again.
Chris - I'd never thought about it from the perspective of an astronomer. And so this is the time to go or at least the time to observe because you've got uninterrupted 24/7 viewing.
Matt - Absolutely, yeah. The South Pole in the winter is one of the best places on earth to observe the sky. There are lots of cosmological and astronomical experiments down at the South Pole because it's astonishingly dark and dry for months at a time.
Chris - I know what I think about the answer to the next question, but I'm going to ask you: it's that time of year again, clock change time. Some people are manoeuvring to stay in one time zone all the time. Are you a fan of changing the clocks or would you prefer to be on one time all the time? And what time would you choose?
Matt - So I think I can answer this with two different hats on: my personal and professional. And they're both the same answer. So, personally, I quite like the clock change. I think there's something quite cosy about wintertime and it getting a bit dark earlier.
Chris - You like that extra hour in bed, don't you, in winter?
Matt - That might be part of it. But also, professionally, from an astronomical star gazing point of view, having the early nights in winter means more hours of darkness to see the beautiful night sky.
05:57 - China's single time zone
China's single time zone
Rana Mitter, Harvard University
For millions of years, life on Earth has evolved to align itself with the day/night cycle. But with the advent of timekeeping devices independent from the passage of the Sun and artificial sources of light at night, humans have been fighting the instincts of their body clocks. China is of particular interest here where, despite its land mass being spread across 5 different geographical time zones, the authorities have decided to establish a uniform timezone across the country: which is called Beijing time. Chris Smith spoke to Rana Mitter, professor of US-Asia relations at the Harvard Kennedy School...
Rana - China itself is, at the moment, either the most or possibly the second most populous country in the world. It's got something like 1.3 billion people. It's being closely lapped by India, which may even have exceeded it in population, but it's still a huge number of people. It goes all the way from the Western side which borders India, the Northern side which borders Russia, and the Eastern side which gives onto the Pacific Ocean. So China's a tremendously large land mass, but it is not a place that has lots of variant time zones. Officially speaking, the entire country, which ought to have really five time zones, just has one.
Chris - What's the impact in practical terms of life under that time regime? If one takes an example of, I'm getting up in the morning in Beijing and it's daybreak, what will it be like for the people at the extremes of the geography?
Rana - What it means is that if you are in the capital city, Beijing, or one of the other major cities of China that's basically on the same longitude, in other words, somewhere like Shanghai or Guangzhou, previously known as Canton, which is on the South coast, you won't actually notice too much that is different from a normal day anywhere else, the reason being that essentially the time zone is set around you. But if you go all the way to the far Western side of China, the territory known as Xinjiang, there you will find that, in practice, although everything runs on Beijing time, in fact, you might find that actually people there refer to their own time as being two hours behind Beijing time. In other words, they've invented their own unofficial time zone. Essentially, people begin to adapt a little bit, but it's worth noting that China is a culture where, broadly speaking, people tend to get up quite early for work when the light makes it possible, work through the day, and then come home relatively early as well. It's not necessarily, in most cases, a very late night culture. I should say that this is something that, in historical terms, is relatively new. Beijing time, the one time zone that China has, only existed in that form since 1949, the year of the Communist revolution when Mao Zedong, the revolutionary leader of the Chinese Communist Party, conquered all of China. He had a revolutionary army that defeated the existing government and brought his communist party to power. He founded the People's Republic of China. that of course is still the government of China today. Now, up to that time, and certainly in the first half of the 20th century, China had five different time zones. So it's much more like America. But Mao decided as the leader of China's revolution that he wanted all China to feel unified, to feel like one country, and one way that he made that happen was to insist that the entire country must share one time zone.
Chris - And how did that go down?
Rana - The early period of the People's Republic of China was a term of immense change in general. So we have to think about the change to a unified time zone as part of a wider set of changes around time and space - makes it sound a bit like science fiction - what I mean is that people started to think in new ways about the time, but also in new ways about the size of their own country. Don't forget that, when the time zone was imposed in 1949, the vast majority of China's population, maybe 90%, lived in the countryside. They were agrarian rather than urban. And that meant that, in practice, it didn't really matter often quite what exactly the time was because you'd get up with the sun and go to bed with the dark. Even running water and electricity were not always widely found. So we need to think of this as a system that was imposed on a country where many people would not regard looking at a clock or a watch as necessarily the most important way for them to tell what the time was. Of course, as time went on and China became more industrialised, more urbanised, more people became caught up in what you might call the regime of modern time. And by regime I mean the way of thinking about how you look at your watch, you look at your clock. But by that stage, the regulation had already been introduced and that meant that people got used to it as people tend to with things which are part of the furniture, so to speak. They don't necessarily rethink what they have been told to do in terms of their everyday lives.
Chris - Is it, in the more modern era, having any kind of impact on business, on people's ability to conduct their affairs when time is so shifted in daylight terms across the country in that way? People in the far west, are they being impacted by this as we move into a more modern way of working?
Rana - Overall, I don't think that most Chinese think that potential time zone differences are a really major part of what gets in the way or helps them out with their particular issues or businesses or ways of life. You have to remember that many things operate in China these days on a 24 hour basis. It's got one of the world's most sophisticated electronic payment systems, people now trade day and night. So the question of morning and night is not irrelevant by any means, but it's rapidly becoming subsumed by aspects of modernisation through technology.
Chris - Do they do DST in China? Do they change their clocks like we do?
Rana - China does not do DST, Daylight Savings Time. It did try it as an experiment for about five years or so from the late 1980s to the early 1990s, but essentially found it was too disruptive from their point of view so they abandoned it. So now, no, China does not set the clocks back or forward in the way that happens in North America or Western Europe.
Chris - Do you see any of this changing in the near future? China embracing time zones like the other big continents or or doing DST?
Rana - Of the various reforms and changes which are likely to come to China, which could be in the fields of economics, international relations, a whole variety of changes of things that concern people on everything from the possibility of a conflict with the United States to attempts to try and shore up the economy, which has been doing quite badly recently, all of those, I think, crowd out attention on things that don't have some immediate pressing, urgent need. And my sense is that a discussion of time zones is really not something that China has had much of a conversation about in recent years.
13:22 - Railways and World Wars caused changes to time keeping
Railways and World Wars caused changes to time keeping
Sean Lang, Anglia Ruskin University
But where did the idea of daylight saving time - or DST - come from in the first place? Chris Smith caught up with the historian Sean Lang at Queens’ College, Cambridge…
Chris - We timed it perfectly, Sean. We've just heard about time as it relates to the planet and why we have day, night, and seasons and so on. But in terms of our human concept of time going way back in time, how does that begin?
Sean - In terms of day and night as the most basic element of time, that seems to go right the way back to neolithic times because obviously you see and you're working through the day. Things like the development of light and candles enable you to extend your living life as it were, into the hours of darkness, but the idea of day and night is something pretty constant until the industrial revolution. And that's when it's first seriously challenged when you can have a working day which doesn't end at dusk, which was the agricultural working day, but to have steam engines which keep going through the night so that you can have the night shift and a complete change in people's living patterns, which at first was very traumatic. This was totally new. Some people can still remember the knocker up, who would come along with a long pole in order to knock on your window to get you up for the very early shift or during the middle of the night. So the concept of day and night is fairly constant until industrialisation changes it and blurs the distinction.
Chris - So it's the industrial revolution that means we need time?
Sean - Absolutely. And this is why you get this huge expansion of clock building and putting clocks up in very prominent places. Now, the best known one around the world is Big Ben. Strictly speaking, that's the bell, but you know what I mean: the parliamentary clock tower. But why have a clock tower? Because the measurement of time was linked with power. So you have that move away from time zones within England because before the railways there were different times. Time was different in different parts of the country, and it's the railway which requires you to have exactly the same time in different parts of the country.
Chris - I actually read that the West country is half an hour different in terms of sunrise and sunset than the East of the country. And so that was the reason we would've had time zones in our country.
Sean - Absolutely, yes. Not time zones marked on the map in the way they are nowadays, but that concept that it was different. But with railways you had to have it and of course with greater speed it was all the more important which was the big Victorian obsession. This is why stations have big prominent clock towers. Towns would build up clock towers just on their own, sometimes on top of buildings, but sometimes just standalone clock towers. And even out in the empire again, clocks, efficiency, trains which ran absolutely to the minute and could be depended upon, these all gave an impression of British power, British prestige. So there was a political side to the control of time and the very public display of your control of time with a big prominent clock tower.
Chris - I always thought that clocks were valuable. They cost a lot of money. They were hard to make, people couldn't afford them. So you just put one big prominent public clock. That does align with what you're saying, but it also served a purpose.
Sean - Absolutely it did. And this would be provided by the local town council usually as a municipal thing, and the town councils also provided you with public health through provision of parks and clean air and what have you. It's all about the power, if you like, of the state. And as for clocks and watches, personal ones, as you say, they were very valuable. The first watches are pocket ones, often made of gold or silver or something like that and very valuable, often being stolen. Not until the first World War do you get the wristwatch because, in the trenches, soldiers needed to know the time, you had to coordinate attacks and things like that, so they needed a reliable watch. But it was no good having it in a waistcoat pocket in your uniform, so you have it on your wrist. So it's a very practical thing which is developed and pretty much kills off the pocket watch.
Chris - Did Britain/England effectively then export time around the world? Because it dominated the world so much at the time when all this was going on?
Sean - There is a sense in which that's true because of the sheer extent of the empire. Now obviously other Europeans were also developing, America's developing clocks and watches and what have you. But for much of the empire, the concept of Western time, and it is Western time based on the Greenwich Meridian, it is part of the image, if you like, of British prestige. India, for example, there's a very different concept of time. And essentially Indians had to fit in with the Western, the British concept of time, dates, years, how old you are and all the rest of it for the purposes of classification.
Chris - When did we start fiddling around with daylight saving then, and why was that introduced?
Sean - Daylight saving is an idea which was put forward before the first World War. And, in fact, it was originally muted as a sort of satirical thing by Benjamin Franklin in the 18th century. Daylight saving, as we know it, is a product of the First World War. There'd been some playing about with it in Canada and proposals in New Zealand, but it wasn't adopted. It's brought in as part of a way of saving energy and in particular extending the working hours in the factories, that sort of idea. And in that sense, it's part of the idea that all of society is in the war. This is total war and of course will be again in the Second World War. The Germans actually started it, and their allies, the Austrians and the Hungarians, and then the British and French fighting them again followed it as well. And it's a way of regulating people's lives. Another thing which was brought in in Britain at the same time was about opening hours for pubs, which before then could open as long as they liked, and did. So it's part of this way in which the state is, thanks to the First World War, really controlling every aspect of your life, even time itself. It's quite a powerful statement.
Chris - So DST comes in with World War I. Was it then maintained after World War I or did we retrench it after World War I and then bring it back at some point? How did that work?
Sean - It was retained and then actually in the second World War it was extended because, again, the second World War really is sort of mobilising the whole of life. And so it's sort of kept as an economic measure. There was an experiment in my childhood in 1973/4, around about then, when they did try getting rid of it and just keeping the the same hour through the year and I can well remember getting up and going to school in the dark and it wasn't much fun and there were accidents and things, so that's why the experiment wasn't repeated, though I know it's something which people always keep talking about. But yeah, so it's basically a wartime measure, which we were then left with like many things like opening hours for pubs!
20:17 - Is daylight saving a detriment to our health?
Is daylight saving a detriment to our health?
Beth Malow, Vanderbilt University Medical Center
So, what impact might meddling with the clocks - and our own body clocks - have on our health? Beth Malow is the director of the Sleep Disorders Division at Vanderbilt University Medical Center. Beth argues that it is time to abolish the changing of clocks and adopt permanent standard time in the United States. Chris Smith began by asking her about the impact that changing clocks can have on our health...
Beth - I like to think of it as two different effects: there's an acute effect, meaning the abrupt change, and then there's more of a long-term chronic effect. Even though it only seems like an hour shouldn't be that disruptive, we can see an uptick in the numbers of strokes and heart attacks and people who just feel off balance/off kilter. We also see car accidents go up and medical mistakes that people make in the hospital, and it's worse when we spring ahead in March maybe because we're also losing an hour of sleep. There is a more long-term effect that lasts basically eight months of the year when we're on daylight saving time. And again, people would think, 'Well it's one hour. I get used to it, I get over it and I'm done.' But we need morning light to wake up and feel good. It boosts our mood, it helps us actually get to sleep easier the following night, and all of that is disrupted when we shift the clocks.
Chris - What effect is that going to have on my physiology?
Beth - Come March, we're going to have that light taken away from the morning and moved to the evening. First of all, it affects our mood. We give light boxes for seasonal affective disorder, a form of seasonal depression in the morning. That's when we need our light to help us wake up, get going, and feel better. And then we also see that there are increases in different medical conditions. So, for example, we see more obesity, more problems maintaining your weight, we see more diabetes, we see more problems with heart disease. And this is all felt to be related to either not getting as much sleep as we need because we're not getting that morning light and not getting to bed at a good hour, or what a lot of scientists call being misaligned, being out of sync with the outside world because now we're artificially moving our clocks an hour later.
Chris - Why do we do this, then? Why do we subject ourselves to these clock changes? Arguably, if you've got the sorts of effects that you are seeing, would we not be better off sticking to one time?
Beth - You make a great point. A lot of it is inertia: doing the same thing we've been doing for a long time. We have to choose between being on daylight saving time all year round and being on the standard time all year round. And even though, as a sleep health expert, I can make an argument for staying on the standard time all year round, there are arguments that have been made for being on daylight saving time, particularly having that light later in the day for golf games and shopping and various other things. If we keep doing what we're doing, we don't have to have to choose between one or the other, which can be very challenging politically.
Chris - But it sounds like there might be a case medically to keep on one time and choose the right time all year round based on what you've been saying?
Beth - Yes. And I also think there have been some studies that have pointed to increased productivity when you're on standard time or when you're getting more light in the mornings.
Chris - Some people have argued that also, human behaviour being what it is, that the original thoughts about having more time with light at certain times of the day than others just don't stack up in terms of how our behaviour is changed. The morning rush is quite a compressed activity early on in the day and is therefore safer than the afternoon journey home. And that includes schools coming out, people coming home from work and so on. And so actually, people are arguing, having more time at the end of the day might be a better option than more time at the beginning of the day with daylight because perhaps people would be more active, also there would be more light to light that journey home and keep the younger people safer?
Beth - I think it goes both ways. With the abrupt change, there's going to be some change in the safety issue and you can't really get away from it. It's going to affect one side or the other. In terms of what you do when you move your light for eight months of the year to the afternoon, I think you could argue it again both ways. You could look at the kids who are really sleepy and sleep deprived and have very early school start times so it's dark when they're trying to go to school as opposed to the afternoon where at least when they're getting out of school it's lighter. It's hard to know. And I think it also depends on where people live. I know that the traffic accident data has been one of the hardest to interpret. The health effects are a lot stronger for standard time.
Chris - So that's presumably what you would wish for if you could wave your magic wand and we stuck to one time zone, no time changes indefinitely thereafter. That's what you'd vote for?
Beth - Yeah, I would vote for standard time. I feel like it's the healthier choice overall and improves mental health, physical health and at least some aspects of safety and productivity.
Chris - Wouldn't you miss, though, that extra hour in bed that you get in the autumn when you know that you don't have to get up quite so early? It's a fallacy, but it it's still good, isn't it?
Beth - I know what you're talking about. It makes you want to hit the snooze alarm several times. I think the other thing I try to impress on people is that it's going to be darker in the winter. We can't make the days longer and even if we were to stay on year daylight saving time, that is not going to make us have endless summer or longer days. We're kind of stuck. And to me, I would rather have that light in the morning to help me get up and get to bed at a decent hour. I hope other people would like to have their light then as well.
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