How do daylight saving and time zones work?

Hang on, what just happened? If you live in Victoria, NSW, South Australia or Tasmania, you’ve just experienced that twice-yearly shock to the system that is the clocks moving back or forward an hour; in this case, waking up to discover it’s an hour later than you’d expected and you’re already late for brunch.

(In the Australian states that have it, daylight saving time always begins at 2am on the first Sunday in October, when the clocks jump forward an hour, and ends at 3am daylight saving time on the first Sunday in April, when the clocks jump back an hour.)

Time can be complicated. We agree to call the period that it takes for the Earth to orbit the sun a “year” and also the time it takes the globe to spin once on its axis a “day”. The precise length of a second has been another matter (more on which later), as has been gaining worldwide agreement on precisely what time it should be where.

A workable, if imperfect, solution are the time zones that divide the globe into segments. Time shifts forward (or backwards) as you cross a boundary from one zone to the next, usually by an hour, though not always. The solution is complicated by another division around the globe: nations.

China, for example, has just one time zone stretching over 5000 kilometres east to west, meaning the sun rises at 6am in (east-coast) Shanghai but at 7.30am in (western) Chengdu. It once had several zones to accommodate its vast girth, but the communist government scrapped that notion in 1949, leader Mao Zedong declaring a single time zone would aid national unity. Australia, conversely, divides its 4000-kilometre-wide mainland into three standard time zones, so the sun roughly rises at the same hour of the day, looking at a clock, in Sydney as in Perth.

“Time zones are so interesting,” says Dr Emily Akkermans, from the Royal Observatory Greenwich, in London, where she is the official curator of time. “I love studying the maps and tracing the time zone boundaries. It’s great to look at these from different periods because this shows how they are not fixed and can be changed to reflect political, cultural or geographical priorities.”

Complicating matters further is daylight saving time, which turns Australia’s three standard time zones into five when it’s in play. Some people (mostly in Queensland and WA) firmly reject the very notion of daylight saving; by contrast, there’s a push in Britain to wind the clocks forward during daylight saving not just one hour but two – so-called Churchill Time, named for the former British PM’s initiative to make the most of productive daylight hours.

How did time zones come about? Why is daylight saving contested? Why is the International Date Line so squiggly?

Who invented time zones?

In the 1952 western High Noon, in the frontier town of Hadleyville the telegram arrives at 10.40 in the morning. A villainous outlaw fresh out of jail is due in town at noon. Will the hero, a town marshall played by Gary Cooper, stand his ground? As the countdown begins, we see clocks tick, pendulums swing and Kane anxiously consult his fob watch. Time is of the essence in this drama. Yet, in the era the film was set, the 1870s, time across the United States was, well, a mess. There were, for example, 80 or so standard times used by rival railway companies, usually based on the time at their headquarters.

The pre-industrial era of local time determined by the sun’s position – midday with the sun directly overhead – was colliding with a faster, increasingly connected world, with no agreed “standard” time as there is today. In the midwest US city of St Louis, where railways converged from north, south, east and west, “station clocks once showed no fewer than 14 different times,” writes Professor Graeme Davison in his 1993 history The Unforgiving Minute: How Australia Learned to Tell the Time.

In Britain, the Great Western Railway had introduced a standard time along its route from London to Bristol in the 1840s, known as “railway time”, although, even then, some villages adopted clocks with two minute hands: one central, one local.

Seeking uniformity for the US, a man called Charles Dowd succeeded in lobbying railway officials to mark out four time zones – Eastern, Central, Mountain and Pacific – in 1883.

Meanwhile, Canadian railway engineer Sandford Fleming had grander ambitions: to impose an overarching order on the Earth’s underlying time differences. Fleming, who knew the Earth spun west to east at 1 degree every four minutes, proposed breaking up the globe into 24 one-hour zones, divided by lines called meridians, which are the basis for differences in world time zones today.

To be on the same page about time, nations would have to agree on a single prime meridian, the point at which time would, essentially, “start”. But this was no easy feat. Over the centuries, many city-states, empires and nations had settled on their own prime meridians for mapping and navigation. There was Ujjain, for example, used by astronomers in India, and the Ferro meridian in today’s Canary Islands, which Europeans once regarded as the westernmost point of the world.

The solution came after Fleming joined forces with the US’s first chief meteorologist, Cleveland Abbe (who had studied with the influential Russian astronomer Otto Struve) to lobby for an International Meridian Conference in Washington DC, attended by 26 nations, in 1884. The favourite was clear. By this time, Emily Akkermans tells us from London, “nearly two-thirds of the world’s shipping used maps and charts based on the Greenwich Meridian. It was therefore a practical choice that the delegates voted for, although not all agreed on Greenwich. France and Brazil abstained, and the Dominican Republic (then San Domingo) voted against.”

The Paris meridian, which France stuck with until 1911, is today marked by 153 bronze discs set in pavements in a north-south line across the city. In London, meanwhile, visitors to the Royal Observatory in Greenwich can straddle the line in the ground that traditionally marked zero degrees longitude and see the telescope used in the 1850s to define that line, which used spiderwebs as the crosshairs through which astronomers observed the transit of the stars. “It was important to time the exact moment a star disappeared behind a cross-hair,” says Akkermans. “They tested silk, metal threads and human hair but the spiderwebs were stronger, thinner and more uniform.”

Today, defining the meridian is a high-tech pursuit – satellites not spiderwebs. In the mid-’80s, the world’s co-ordinate systems were updated such that the prime meridian now actually passes 102.5 metres to the east of the meridian at Greenwich.

Meanwhile, today’s timekeepers rely on atomic clocks, super-accurate devices that measure the oscillations of things called “cesium-133 atoms” to define the length of a second, which was previously calculated as 1/86,400 of a solar day. Global time is no longer referenced by a standard GMT but by Co-ordinated Universal Time (UTC), introduced from 1960 and determined by a select group of atomic clocks.

In Australia, the job of regulating time falls to Dr Michael Wouters and his team at the National Measurement Institute in Sydney, Australia’s peak measurement body responsible for biological, chemical and physical measurement. “The International Bureau of Weights and Measures, which is responsible for calculating Co-ordinated Universal Time, collects all of these measurements from labs like ours around the world, makes an average of them, and then tells you what your difference is with respect to that, and that average is UTC,” he tells us. UTC is then broadcast by these select atomic clocks through GPS, the internet and radio signals. Depending on daylight saving hours, eastern Australian time is UTC + 10 or + 11.

Even a tiny inaccuracy in how clocks are synchronised, a millionth of a second over three years, can make a difference to industries that rely on near-perfect time keeping, such as the power grid and mobile communications, says Wouters. “You need synchronisation at microsecond level for things to work correctly.”

Time zones, however, are far less scientific. Few neatly align with Fleming’s 24 meridians as he might have hoped. Determining where they fall is “really just a national decision about what time zone to have within their borders”, says Wouters. Hence, China deciding to use just a single time zone, as does India.

In the US, time zones are overseen by the Department of Transportation, to whom you can apply to have your zone changed. Sometimes the US creates a whole new zone, as it did in December 2000 with the Chamorro Time Zone, for the island of Guam and the Northern Mariana Islands. North Korea has switched back and forth from “Pyongyang Time” in 2015 to re-aligning with South Korea in 2018; Venezuela set its clocks back 30 minutes under then-president Hugo Chavez in 2007, but reversed the move in 2016.

Nor is the International Date Line set in stone. Established by international treaty in 1884, it mostly runs at 180 degrees longitude north to south, on the opposite side of the globe to Greenwich, skirting continents as it forms the boundary between one calendar day and the next. In the Bering Strait, between Alaska and Siberia, the date line bisects the two major Diomede Islands, which are now nicknamed Tomorrow Island (on the Russian side of the line) and Yesterday Island (on the US side).

The date line is marked by detours and cut-outs here and there, mostly for reasons of convenience. In the 1990s, the Pacific nation of Kiribati moved the line east to include its easternmost islands, causing the date line to dogleg back and forth; in 2011, Samoa did the same, forcing the line to skirt it to the east so that it could be in the same calendar day as its major trading partners, New Zealand and Australia. “It was a deliberate decision to have a date line that did not cross any continents,” says Akkermans, “and it deviates around islands and territories, who can choose on which side of the date line they would like to be.”

When did time zones come to Australia?

In 1897, Charles Deland, a miner at Menzies, near Kalgoorlie, arrived at church to find the sermon nearly over, writes Graeme Davison in The Unforgiving Minute. Deland later explained to his fiancee: “The post office time is usually 40 minutes behind town time & mine time is just between the two. I went to church by town time and found they had started by the post office time. The irregularity is because of the mine being taken from the sun & post office time from the Perth time.”

The story was similar in towns across the continent, including Broken Hill, where the railways ran on Adelaide time; the post office on Sydney time; and the mines on “local”, or solar, time. Any public clocks in the early colonies’ cities were set by their makers and prone to breaking down. “There are but five public clocks in Sydney, three of which have not shown any symptoms of movement for the past five or six days,” grumbled The Sydney Morning Herald in 1844.

By the 1870s, the big cities were sending telegraph signals from government astronomical observatories to their public clocks and to an instrument called a time-ball, which had a huge ball that dropped down a pole at an appointed hour (usually 1pm) and which could be seen by ships at sea (in Williamstown in Melbourne, say, or on the Rocks in Sydney). No one was in a hurry to standardise time.

“Even as late as the 1880s, Australia is still more like an archipelago of islands than it is like a completely united country,” says Davison, an emeritus professor of history at Monash University. “It’s only in 1878 that you finally get direct railway communication between Melbourne and Sydney and, shortly after, Adelaide. Even within, say, Victoria or NSW, different communities will keep their own time.” (It was a “chaos”, noted The Telegraph in Brisbane, that “caused much friction”.)

An Australian who had been in touch with Sandford Fleming was Charles Todd, South Australia’s postmaster-general and superintendent of telegraphs. An astronomer and engineer, he had overseen the Overland Telegraph Line that linked Adelaide to Darwin then Indonesia, via one of the first subsea cables, and on to London. At a conference in 1891, he proposed that Australia be united under one time zone based on the 135th meridian, which, conveniently, ran through his home state.

“Todd had an interest in trying to make South Australian time the time for the whole continent,” Davison says. “Now, that was going to be very difficult because the difference [in solar and standard times] between, say, Brisbane and Adelaide, let alone [Brisbane and] Western Australia, was really a bit too much. The Queenslanders were the first to object to Todd’s proposal. And the division of opinion on that led towards the final decision to have three one-hourly time zones rather than just one or two.”

The following year, a group of surveyors took up a version of time that seems not unlike that in the US: Western time would be at 120 degrees longitude, Central at 135 and Eastern at 150 and these would be eight, nine and 10 hours, respectively, east of Greenwich. Eventually, the colonies made these standard times into laws, aligning on one discombobulating evening. At midnight on February 1, 1895, NSW clocks stopped for five minutes and Adelaide clocks for 14 minutes and 20 seconds while at 20 minutes to 12, Melbourne clocks whizzed forward to midnight. It was “a busy night for Australian clockmakers and a bewildering one for many citizens,” writes Davison in his essay Punctuality and Progress: The foundations of standard time in Australia.

Not everyone was happy. Some South Australians felt they had been cast into a time warp: having to wait an hour longer than their eastern counterparts for a telegram from Britain, for instance, as their post office was still closed and, even worse, finishing footy matches in the dark. As The Advertiser noted in 1899, “An agitation has been raised by commercial men and fomented, it is said, by cricket and football circles that we should move up half an hour nearer to Melbourne time, and to also obtain half an hour’s extra daylight.” So in 1899, a new half-hour time zone came into effect in South Australia (and the Northern Territory, which was then part of South Australia): Australian Central Standard Time, 9½ hours ahead of Greenwich. Broken Hill, although in NSW, also opted in because of its rail links with Adelaide.

“What’s surprising is that Adelaide didn’t come aboard and observe Eastern Standard Time,” notes Davison, “because a half an hour difference hardly matters. I’m not sure how you would explain the fact that they’ve continued it – but its origin is partly explained by the fact that it was with Charles Todd that the argument began, and the South Australians were not going to be content to observe Sydney time.”

Drive along the Eyre Highway on the Nullarbor Plain and you’ll reach another pocket of the nation that has not signed up entirely to our mainstream time zones. Central Western Standard Time is an unofficial, albeit clearly signed, zone that applies at roadhouses for some 340 kilometres of WA up to Border Village roadhouse near the SA border. Clocks are set to UTC+ 08.45, 45 minutes ahead of Perth and 45 behind Adelaide, a difference thought to be a relic of an old telegraph station caught between time zones at Eucla. “It was funny at the beginning because I have never been in another place with three clocks,” says the duty manager at Eucla Motel, Gianfranco Nicolini, originally from Chile. “Sometimes when guests arrive at the cafe, they ask, ‘Well, I don’t know if I have to have lunch, breakfast or …’ It’s something iconic from this place.”

Down the highway at Cocklebiddy Roadhouse, site manager Christine Warren warns travellers who phone ahead to plan for “Cocklebiddy time”. “If they don’t listen to you, they’ll turn up and we’re just about ready to close.” Some customers can get annoyed, she adds. “If they carry on like a pork chop, I just say, ‘Look, if you’ve got a problem with it, take it to your member of parliament and let them sort it out.’”

When did daylight saving come into the mix?

In March 1784, American statesman and inventor Benjamin Franklin was woken by noise at 6am at the Hotel de Valentinois in Paris. Not typically an early riser, he was surprised that at this hour his room was filled with light. This gave him an idea. The previous night, he had been at a soiree where a new type of bright-burning oil lamp had been on show. How economical was it? And how economical, he wondered, were the candles that the typically night-owl Parisians routinely used for light? He calculated that between any given March and September, they burned a total 64 million pounds of wax and tallow for 128,100,000 hours: “An immense sum! that the city of Paris might save every year, by the economy of using sunshine instead of candles,” he wrote in a satirical letter to The Journal of Paris, suggesting instead that people rise with the sun and a tax be put on window shutters.

Many years later, across the globe in New Zealand, post-office shift worker and entomologist (insect expert) George Vernon Hudson had a more serious idea about capturing the benefits of daylight – by moving the clock. He proposed “seasonal time”: a two-hour clock change from October to March. Milkmen might suffer, he told the Wellington Philosophical Society in 1898 (because winding clocks forward would mean darker mornings) but they were a minority; anyone who regarded “an abundance of outdoor recreation” as key to “human health and happiness” would surely back the scheme.

While New Zealand had been one of the first nations to standardise its time by reference to Greenwich, in 1868 (well before the big meridian conference), on daylight saving it was slower to move. The first place to formally “save daylight” is generally agreed to have been the town of Port Arthur in Ontario, Canada, today called Thunder Bay, when an amateur athletics fan and former teacher, businessman John Hewiston, led the charge. Britain was moved to action by a builder who liked horseriding: William Willett, the great-great-grandfather of Coldplay singer Chris Martin whose hit songs include Clocks. Willett’s self-published pamphlet The Waste of Daylight put daylight saving on influential radars.

Willett had been on a morning ride when he’d noticed that the blinds of most houses were still drawn. “Now, if some of the hours of wasted sunlight could be withdrawn from the beginning and added to the end of the day, how many advantages would be gained by all,” he wrote in 1907. He lobbied for clocks to be moved forward 80 minutes in four weekly increments from April and then back in September, which he calculated would “save” 210 hours of daylight a year.

In the end, though, it was not health or leisure but war that kicked daylight saving into being. “It is one of the paradoxes of history,” Winston Churchill later opined in a tribute to Willett, “that we should owe the boon [of daylight saving] to a war which plunged Europe into darkness for four years.” In 1916, wartime Britain turned its clocks forward an hour at the start of summer, to conserve fuel. (In World War II, it went even further, with Churchill mandating the clocks stay two hours ahead during daylight saving hours, so-called Double Summertime.)

When Australia followed suit in 1917 it was barely a month before the complaints began, writes Graeme Davison: mostly from dairy farmers, who claimed their early-rising cows were less productive; and cinema and restaurant owners, who claimed patrons were lingering outdoors instead of spending their wages with them; and residents who said “skylarking” youths were keeping them awake in the evening; as well as mothers of sleepless children; and shift workers.

Daylight saving was dropped after the war but similar voices led protests when it returned in 1942, again as a wartime measure. It was revived in the modern era when Tasmania became the first state to reintroduce it, during drought in 1967, to reduce pressure on the state’s hydroelectric electricity supply by relying instead on later daylight hours in summer. For the rest of the country, “by the 1970s it comes back again”, Davison tells us. “There’s a lobby group, the Daylight Saving Association, pushing for it. In a broader sense, you get the introduction of flexi-time in offices, the extension of night shopping hours, new interest in techniques of time management – all of that tends to contribute to the idea that organising time in a rational way is a good idea.”

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Again, not everyone was on board. WA, which had dropped out of daylight saving in both world wars, trialled it again but has rejected introducing it long-term in four referendums, most recently in 2009. In Queensland’s 1992 referendum, the “yes” case argued that local businesses would benefit from being in chronological alignment with their neighbours in NSW; the “no” case complained that daylight saving would condemn children to finishing school during the hottest part of the day and that “for many elderly people” it would be an “inconvenience requiring changes to daily living routines”. The “no” campaign won with 54.5 per cent of the vote.

In Britain, meanwhile, Conservative MP Rebecca Harris brought a bill to parliament in 2012 calling for a cost-benefit analysis of potentially moving the clocks forward one hour year-round, a proposal that was widely supported but failed to proceed due to political shenanigans. In March this year, British Labour MP Alex Mayer revived the issue, calling for an even more extreme measure: moving the clocks forward two hours, meaning even when they went back one hour in winter they would still be an hour ahead of UTC, so-called “Churchill hours”.

Even Donald Trump has an interest in daylight saving, apparently supporting efforts to put the clocks forward one hour year-round. “Very popular and, most importantly, no more changing of the clocks, a big inconvenience and, for our government, A VERY COSTLY EVENT!!!,” he wrote on social media in April. Versions of what’s known as the Sunshine Protection Act have been debated by Congress several times but have yet to gain enough support to pass into law.

Meanwhile, even the moon is about to get its own time zone: Lunar Co-ordinated Time. In 2024, US Congress asked NASA to oversee the creation of a standard time on the moon given the many nations that will be involved in working on it in coming years. This will require a lot of cleverness, observes the United Nations Office for Outer Space Affairs. “Place two perfectly synchronised clocks – one on Earth and one on the Moon – and, after just one Earth day, the lunar clock would be ahead by about 56 microseconds. That might not sound like much, but for spacecraft navigation, this tiny discrepancy could be critical.”

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