By Lucy Rodgers BBC News

Without it international travel would be in turmoil and calling friends in faraway places at the right time impossible. Exactly 125 years after the Greenwich Meridian line was drawn, how and why did Britain become the centre of time?

At longitude 0° 0' 00", the arbitrary stroke on our maps that passes from pole to pole and bisects the UK, France, Spain, Algeria, Mali, Burkina Faso and Ghana divides the Earth into east and west, just as the Equator splits it into north and south.

This imaginary line now known as the Greenwich Prime Meridian not only allows us to navigate the globe but also keeps the world ticking to the same symbolic 24-hour clock.

But it has not always been so.

Until the 19th Century, many countries and even individual towns kept their own local time based on the sun's passage across the sky and there were no international rules governing when the day would start or finish.

Maps with multiple meridians were confusing Enlarge Image

However, with the rapid expansion of the railways and communications networks during the 1850s and 1860s, setting a standard global time soon became essential.

"The world was in a very big mix-up," explains Dr Avraham Ariel, author of Plotting the Globe. "People had lots of prime meridians. Earlier in Europe there were 20 prime meridians. The Russians had two or three, the Spanish had their own and so on."

And so, 125 years ago this week, 41 delegates from 25 nations gathered in Washington in the US for the 1884 International Meridian Conference to decide from where time and space should be measured.

By the end of the difficult summit, which, according to Dr Ariel, dragged on until "smoke came out", Greenwich had won the prize of longitude 0º by a vote of 22 to one, with only San Domingo against and France and Brazil abstaining.

The meeting also agreed Greenwich Mean Time (GMT) would be used as the standard for the world, with the day beginning at midnight at Greenwich and counted on a 24-hour clock.

Political opponents

One of the main reasons for British victory over key rivals Washington, Berlin and Paris, was that 72% of the world's shipping already depended on sea charts that used Greenwich as the Prime Meridian, says Dr Rebekah Higgitt, curator of the history of science and technology at the Royal Observatory in Greenwich.

Greenwich's reputation among seafaring nations and the wide range of maps and charts using Greenwich as the Prime Meridian meant those at the conference "could see that was the way it was going", she says.

Another factor in Britain's favour was that the US had already plumped for Greenwich as the basis for its own national rail time system.

But, as the San Domingo, French and Brazilian votes showed, the choice was not without its opponents.

There remained some desire, particularly among Britain's European competitors, for "something more neutral" - a location that did not have such national ties, Dr Higgitt says.

"France suggested using an older idea of a meridian running through the Canaries - and even after the 1884 conference, Jerusalem was suggested as a site, particularly by Italy."

Opting out

Yet while the conference's Greenwich decision has stood until this day, the ultimate aim of some of those at the conference - a simple centralised system of 24 uniform time zones for 24 hours - never came into being.

LONGITUDE All points on the Prime Meridian are at 0° longitude All other points on the earth have longitudes ranging from 0° to 180°E or from 0° to 180°W The international date line lies along the 180° meridian Meridians of longitude and parallels of latitude together form a grid by which any position on the earth's surface can be specified Unlike the parallels of latitude, which are defined by the rotational axis of the Earth, the Prime Meridian is arbitrary

Over the years, many countries have opted out of the system to demonstrate national independence, keep in time with neighbours or maintain standard days within their borders.

As recently as 2007, Venezuela's president Hugo Chavez shifted the entire country back half-an-hour, while other countries operate similar fractional zones - half-hour or quarter-hour deviations. Yet more, such as China and India, use single time zones even though their territory extends across many hours.

"These things come up. Sometimes it's popular will or sometimes it is government choice," says Dr Higgitt.

"France and Spain should be on the same time as the UK, but it is more convenient to be in sync with those they are attached to by land."

And while such political and practical considerations have caused time zones to change in relation to Greenwich over the years, scientific and technological advances have also challenged Greenwich's role as the centre of time and space.

Leap seconds

Since the 1960s, atomic clocks rather than astronomy have been keeping the world's time and have forced GMT to adapt.

The combination of atomic clocks' super-accurate measurement and the fact that the rotation of the Earth is irregular and slowing mean atomic time and Earth time - and therefore GMT - slowly drift apart.

The Greenwich Meridian has attracted visitors for decades

To keep them in sync "leap seconds" are added and produce a compromised version of GMT called Coordinated Universal Time, which keeps atomic time tied to the Earth's rotation.

On top of such changes to GMT, the advent of GPS technology and its ability to precisely track location has also had its impact on Greenwich as the zero point of longitude.

GPS's World Geodetic System 1984 system now places the Prime Meridian 100m to the east of Greenwich Observatory - away from the line defined by its large "Transit Circle" telescope and its corresponding brass strips straddled by tourists eager to have one foot in the East and one foot in the West.

Dr Ariel argues this renders the historical Prime Meridian no longer meaningful. But Dr Higgitt believes it simply highlights the fact it is not a scientifically-determined line and simply the result of global agreement.

"People stand on it because people think it is a predestined place," she says. "But it has never been official. It just exists in terms of habits and international usage. It is just something that has happened over a period of time."

The 125th anniversary of the Prime Meridian will be celebrated with a talk by Graham Dolan at the Royal Observatory in Greenwich at 1900 BST on Tuesday 20 October.

Below is a selection of your comments.

It is amazing that in this day and age of global devices, from GPS and television, to cell phones and sporting events, we still put up with clocks set to local time and, horror of horrors, daylight saving. One only has to look at an airline itinerary that takes in New York, London, Dubai and Johannesburg to see how ridiculous it is. It is absolutely essential that all the world's countries go over to GMT or its modern equivalent as soon as possible. It would take a couple of months for us in North America to get used to having lunch at 16:00 and going to bed at 02:00, but think of the convenience. I could schedule a phone call to an associate in Zimbabwe for 08:00 GMT knowing that I would catch him before supper. The only unresolved issue would be the 360 degree circle, but that has to be the subject of some future rant.
Frank, Vancouver, Canada

The article overlooks one big advantage of Greenwich for the 0 degrees meridian: it defines an International Date Line (180 degrees) which passes over the fewest and least populated land masses. Having one's feet straddling East/West is bizarre enough, but how about straddling Today/Tomorrow?
Ian Clark, Whitby, England

The location of the prime meridian does have some geographical relevance because of what happens 180 degrees away, the international date line. Having two different dates on one piece of land would be rather inconvenient. This needs to avoid land and although the Pacific is a huge place, there are still many islands that it has to detour around. A Washington meridian would mean a dateline passing through Asia.
Hugh Kennedy, Essen, Germany

Imagine if the meridian were in Palestine - parts of the US (or Brazil and Canada) would be one day and parts the next day off by 23 hours. That would have been nasty. On this count I have to go with our imperial overlords.
Sri, Chennai

Surely the country at 0,0 (lat, long) is the "centre of the world". England has as much claim as anywhere on that line. But being on both the equator and the prime meridian is doubly special.
Ette Nuahs, UK

Surely John Harrison with his brilliant chronometers had something to do with the world accepting Greenwich as the prime meridian?
Barry Bernstein, London

The person who developed the 24 time zones was a Canadian, Sir Stanford Fleming, whose simple idea was adapted at the 1884 Congress. His development was born of necessity, with the development of the train system across the current 5 time zones of Canada. He was accused of being an "internationalist, and a communist for daring to interfere with God's natural work".
Dan McWilliams, Vancouver, Canada

Sir Sanford Fleming was born in Scotland but emigrated to Canada at the age of 18. He proposed time zones at the International Conference. And he proposed Britain due to his heritage.
Neena, Toronto, Canada

The Washington conference may be interesting, but the issue was already a foregone conclusion by then. The real reason the meridian is at Greenwich is that the Astronomer Royal at Greenwich was the first - indeed, really the only - person to have done the research required to calculate navigational tables. He naturally took his own telescope as the baseline, and once the nautical almanacs which resulted were published no-one could be bothered to do the research all over again merely to establish a different base. It's important to note that the meridian is at Greenwich, not Charing Cross: so it honours a great scientist rather than Britain. And who was that scientist? None other than Nevil Maskelyne, the villain of Dava Sobel's popular book Longitude, but arguably the real solver of the longitude problem.
Peter Hankins, Wallington

I believe that another reason that Greenwich was chosen for the prime meridian is that it would be appropriate to locate the center of world time in the great British Empire on whose flag the sun never set.
Allan Holmgren, Burnsville MN USA

GMT became the standard due to Britain's economic, political and especially maritime dominance of the time. I do not think at present that the GMT will be abandoned, as news over the internet still use GMT, CET, EET and so on. As for shifting time due to less power consumption, this is no longer the case. At the time when this practice was implemented lights were the main source of power consumption, these days so many appliances run that shifting time has no effect on saving electricity.
Christos Koumides, Nicosia, Cyprus

Hey, at that time, the British scientists were ahead of all others - AND Britannia ruled the waves. I think the Brits have a right to own this one.
Vikram Modak, Saratoga, California

Shame the UK won't move its zone to match France. More light in the evenings in winter, less power consumption, less depression, fewer suicides, fewer road deaths - lots of benefits, albeit angry Goths. And since this is all arbitrary anyway, if the Scots think this could cause problems in deepest winter with kids going to school in the dark (as opposed to coming home in the dark, which happens to those staying for after-school clubs...), we could always draw a time-zone line across the UK.
Craig, United Kingdom

I invariably fail to comprehend why time zones can affect when schools stop and start. After all, schools set their own actual stopping and starting times. We do not have a regulation of all schools must start at 08.30 and finish at 15.30, so why the fuss about the local time changes must allied to schools. Long time ago, working in Botswana where we did not have winter time, there was a cheer from the students when the head teacher announced that for the next term school would start at 07.30 instead of 07.00.
Jane, Essex

You mention that the 1984 World Geodetic System system now places the Prime Meridian 100m to the east of Greenwich Observatory. As a resident of Lewes, through which the line passes, I was for some time puzzled by the fact that my GPS device disagreed with the local markings and monuments until I discovered this 1984 change. However, you omit to say why our meridian had to move. The answer is, of course, that the Americans set the new standard, and decided that the meridian line to be preserved was - obviously - 90 degrees West.
Ric Bithell, Lewes

I have just had a tattoo done saying 36º35'50"N 4º38'24"W, only to discover by this article that it's actually 100m out... Bugger!
Nial, Sydney

Isn't it ironic that Britain agreed to this international effort to measure world time but can't quite bring itself to use the other internationally recognised system of measurement, the metric system. There is, of course, the fact that Greenwich is in Britain and I guess this wasn't forced on us by the EU... but then the original idea for the metric system was also British and, despite what's said, isn't being forced on us by the EU either. It does show that the Britain has in the past managed to be sensible about adopting worldwide standards.
Alex Bailey, Corby, England

I much prefer the idea of 24 uniform time zones. The counter argument is that the working day in New York would start at 15:00 (i.e. at the start of the day in NY) rather than at 9:00. But the 9:00 start is purely arbitrary anyway. And we'd no longer have to change our watches every time we travel. After all, we don't have "month" zones so that when it's June in Europe it's December in Australasia (so that the snow that falls comes at the "right" time of the year).
Malcolm Hyde, Fillinges, France

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