Changes to the world's time scale debated

 

What is a leap second? The BBC's Rebecca Morelle went to Greenwich's Royal Observatory to find out

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Time, as we know it, could soon be in for a radical change.

This week, scientists at the Royal Society are discussing whether we need to come up with a new definition of the world's time scale: Coordinated Universal Time (UTC).

And the main issue up for debate is the leap second - and whether we should abolish it.

The leap second came into existence in 1972. It is added to keep the time-scale based on atomic clocks in phase with the time-scale that is based on the Earth's rotation.

Atomic clock (NPL) Atomic clocks are much better at keeping time than the Earth

The reason for this is that while atomic clocks, which use the vibrations in atoms to count the seconds, are incredibly accurate, the Earth is not such a reliable time-keeper thanks to a slight wobble as it spins on its axis.

Rory McEvoy, curator of horology at the UK's Royal Observatory in Greenwich, explained: "Since the 1920s, it has been known, and previously suspected, that the motion of the Earth is not quite as constant as we'd first thought."

This means that time based on atomic clocks and time based on Earth drift ever further out of phase over time.

So every few years, before the difference has grown to more than 0.9 seconds, an extra second - called the leap second - is added to snap the two back into synch.

"The International Earth Rotation Service monitors the Earth's activity, and they decide when it is appropriate to add a leap second into our time-scale," said Mr McEvoy.

Split second

Start Quote

Leap seconds are a nuisance”

End Quote Felicitas Arias BIPM

But the call to get rid of the leap second is causing a rift within the international time community, and it will come to a head at a vote at the World Radio Conference of the International Telecommunication Union (ITU) in January 2012 in Geneva.

An informal survey by the ITU earlier this year revealed that three countries - the UK, China and Canada, are strongly against changing the current system.

However 13 countries, including the Unites States, France, Italy and Germany, want a new time-scale that does not have leap seconds. But with nearly 200 member states, this still leaves many others that have yet to reveal their position.

The International Bureau of Weights and Measures (BIPM) in Paris is the international standards organisation that is responsible for maintaining the world's time. It thinks that the leap second should go because these one second adjustments are becoming increasingly problematic for systems that need a stable and continuous reference time-scale.

Clockface The leap second is troublesome for applications that require constant time

Dr Felicitas Arias, director of the BIPM's time department and co-organiser of the meeting at the Royal Society, explained: "It is affecting telecommunications, it is problematic for time transfer by the internet (such as the network time protocol, NTP) as well as for financial services.

"Another application that is really very, very affected by the leap second is time synchronisation in Global Navigation Satellite Systems (GNSS).

"GNSS rely on perfect time synchronisation - and leap seconds are a nuisance."

One problem is that because the changes in the Earth's rotation are not regular, leap seconds are also erratic, and only six months' notice is given for each one.

Diverging time

But the countries that are against losing the leap second, including the UK, say the problems are being exaggerated.

Peter Whibberley, senior research scientist in time and frequency at the National Physical Laboratory, in Teddington, said: "When the UK government did a survey of government agencies, they couldn't find anyone who was concerned with leap seconds. So we don't see the evidence presented for the problems caused by leap seconds as being all that serious."

But decoupling civil time from the Earth's rotation could also have longer-term consequences.

Dr Whibberley explained: "[If you lost leap seconds] UTC would drift apart from time based on the Earth's rotation, it would gradually diverge by an increasing amount of time. Something would have to be done to correct the increasing divergence."

Earth Unlinking time from the Earth's rotation has long-term consequences

Over a few decades this would amount to a minute's difference, but over several hundred years this would mean the atomic clock time-scale and the time-scale based on the Earth's rotation would be out by an hour.

In 2004, the idea of swapping leap seconds for a leap hour in a few hundred years' time was proposed. But Dr Whibberley said most scientists agreed that this would be even more problematic.

He explained: "It was dropped quickly. The general feeling was that you could never implement a leap hour as they are much harder to do than the leap seconds, and if you can't cope with leap seconds, it would be much harder to cope with a leap hour."

One possible solution, if the leap second is abolished, could be to tie in any changes with daylight saving changes - even though this would take place in a few centuries' time.

"Countries could just accommodate the divergence by not putting their clocks forward in the spring, so you'd change your time zone by one hour to bring civil time back into line with the Earth's rotation," added Dr Whibberley.

Dr Arias said it was looking increasingly likely that leap seconds may be voted out in January, but that the meeting at the Royal Society could help to thrash out ideas that could offset any problems this loss could cause.

"The point is we can find a compromise, there are possibilities of leaving the time open for synchronisation in the future," she said.

 

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  • rate this
    0

    Comment number 266.

    @262. nonnamei

    "I'm not saying it's the same, I'm saying it's a similar concept to a leap year the only difference being the quantity of seconds added and predictability of when to add them."

    But there is no predictability about leap seconds. That's the point.

  • rate this
    0

    Comment number 265.

    12, 24 and 60 splitt the best ways to make time most usefull to our needs. 7 day week should be the real issue here and I think the best thing would be 5 day work week and 5 day weekend. The religious 7 day week has no place in secular society.

  • rate this
    0

    Comment number 264.

    A good article -- stuff like this justifies the licence fee.

    Thank you, BBC.

    And some hilarious comments as well!

  • rate this
    +1

    Comment number 263.

    Time flies like an arrow; fruit flies like a banana.

  • rate this
    0

    Comment number 262.

    256.OldFool48

    I'm not saying it's the same, I'm saying it's a similar concept to a leap year the only difference being the quantity of seconds added and predictability of when to add them.

  • rate this
    -1

    Comment number 261.

    @259. likeaflash

    "first they want to tax us more, then cut our pensions, now they are even taking time off our lives"

    Give us back our eleven days!
    http://en.wikipedia.org/wiki/Gregorian_calendar

  • rate this
    +2

    Comment number 260.

    Struth...I wish the people with NO understanding of this article would not bother to post.
    Nobody will notice anything in our ordinary lives, our clocks and watches will still work, time will be the same. It is just the techno world of computers eletronics etc. that is affected.
    Like scientist using a laser to measure distance while the rest of us use a tape measure.

  • rate this
    0

    Comment number 259.

    first they want to tax us more, then cut our pensions, now they are even taking time off our lives

    enough is enough, i say

  • rate this
    -1

    Comment number 258.

    Just a second - can somebody explain this one more time please? I don't understand. I require a leap explanation.

  • rate this
    +1

    Comment number 257.

    As a programmer, I think there could be a whole can of worms to this issue. A bit like the Millennium bug but worse.

  • rate this
    0

    Comment number 256.

    @255. nonnamei
    "253.OldFool48

    Your question is a 'strawman' that's why I ignored it. I know that 'clock time' doesn't change during a leap year, however the *length* of the year changes in a similar way to adding 1 second to a year (we add 86,400 seconds [1 day] during a leap year)."

    But it's not the same. It is irrelevant to the question of Leap Seconds. Not enough space here to explain.

  • rate this
    0

    Comment number 255.

    253.OldFool48

    Your question is a 'strawman' that's why I ignored it. I know that 'clock time' doesn't change during a leap year, however the *length* of the year changes in a similar way to adding 1 second to a year (we add 86,400 seconds [1 day] during a leap year). This is what I'm pointing out.

  • rate this
    0

    Comment number 254.

    How about reps of countries sitting down and working out if changing the clocks by even a couple of hours, might be of benefit and bring more countries in line with each other when it come to light/dark mornings and lighter/darker evenings. You can't win them all but you might be able to get the majority of countries on the same time line.

  • rate this
    0

    Comment number 253.

    @247. nonnamei

    "243.OldFool48

    Re read my post. I didn't say in post 240 that extra seconds are added to clocks. I stated that an extra 86,400 secs is added to the standard years total of 31,556,926 secs."

    Re read my post. I asked - do you change your CLOCK (ie CLOCK TIME) on February 29th. I don't change mine. The TIME doesn't change on 29th February.

  • rate this
    0

    Comment number 252.

    all i have to say to the sientists is for once think of the humen cost and leave things as they are for God's sake

  • rate this
    0

    Comment number 251.

    @248. Eddy from Waring
    "IMO it's all about language and meaning. By what authority does anyone redefine the meaning of a word used by millions?"

    We no longer live in a world in which the average boot size of the first 20 men out of church on Sunday is an adequate standard of measurement for all. There's more to life than ordering a pint or buying wood for shelves.

  • rate this
    -1

    Comment number 250.

    The very idea of abolishing leap seconds - to accommodate the shortcomings of our computers and sat-nav systems - is a huge embarrassment to those of us still committed to physical reality. A growing part of mankind seems perfectly happy to abandon the idea that we live on a planet, preferring instead to take up permanent residence in some fictional, perfectly timed cyberspace. Shame on you!

  • rate this
    +2

    Comment number 249.

    I don't see why this is even an issue. We have a variety of time references at the moment - UTC, which governs Civil Time, the International Atomic Time (TAI) which has been drifting away from UTC since its adoption over 50 years ago, and GPS time which, like TAI has no leap seconds but is offset from TAI. Astronomers use a variety of other time references.

  • rate this
    -1

    Comment number 248.

    "It's not about language, it's about measurement."

    ==========

    IMO it's all about language and meaning. The word "second" as a simple matter of fact of usage, means one sixtieth of one sixtieth of one twenty-fourth of a day. By what authority does anyone redefine the meaning of a word used by millions? "Presumed consent" is the only coherent basis, but I see no evidence of that consent.

  • rate this
    0

    Comment number 247.

    243.OldFool48

    Re read my post. I didn't say in post 240 that extra seconds are added to clocks. I stated that an extra 86,400 secs is added to the standard years total of 31,556,926 secs. The only use of the word 'clocks' in post 240 is regarding 'internal clocks' used to determine the passing of time by technology.

 

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