[ntp:questions] Leap second talks are postponed

Marc Brett marc at fordson.demon.co.uk
Sun Nov 20 08:24:08 UTC 2005


Leap second talks are postponed 

Consideration of a proposal to redefine everyday timekeeping by scrapping leap
seconds - small changes made to clock time - has been postponed. 

A working party weighing the proposed change to Coordinated Universal Time (UTC)
has decided more time is needed to build a consensus on the issue. 

Leap seconds synchronise clock time with solar time used by astronomers. 

The US delegation to the International Telecommunications Union (ITU) wants to
abolish these adjustments to UTC. 

Tidal friction is causing the Earth's rotation to slow down. This means that
everyday timekeeping, based on the rotation of the Earth (solar time), tends to
drift out of sync with respect to the time kept by atomic clocks. 

More time 

For this reason, the standard for everyday timekeeping, known as Coordinated
Universal Time, or UTC, must be adjusted every so often. 

This takes the form of individual seconds being added or subtracted from the
length of a day, either a 30 June or a 31 December. The first leap second in
seven years will be added at the end of 2005. 

In this way, clock time is kept in step with solar time, which is used to
precisely point telescopes and to find satellites. 

The new proposal, originally tabled for discussion at the ITU meeting in Geneva
last Wednesday, proposes that the maximum difference between UTC and solar time
be increased to an hour. 

In a statement, the ITU working party said: "The working party has discussed the
proposed change and options, and decided that more time is required to build

"In addition, the forthcoming leap second just prior to 1 January 2006 provides
an opportunity to further document current problems." 

Welcome postponement 

Dr Mike Hapgood, secretary of the Royal Astronomical Society (RAS) in the UK,
welcomed the decision to defer the discussions until a later date. 

"It's what we were seeking, so that's good from our point of view," he told the
BBC News website. 

It is understood that software issues with the US global positioning system
(GPS) sat-nav network are partly driving the proposal. 

As well as satellite positioning, GPS provides a time signal, and some software
systems used in the sat-nav system find it hard to cope with leap seconds. 

Leap seconds also create difficulties for computer programmers making
calculations using time. 

However, without the leap second, astronomers would lose track of distant stars
and spacecraft. 

And the idea of clock time following solar time is also deeply embedded in
contemporary culture. Researchers estimate that the difference between UTC and
Earth time could increase to about an hour within several hundred years. 

Daniel Gambis, of the Earth Rotation Service in Paris, which decides when to add
or subtract leap seconds, told the BBC: "For me, it would be a problem if the
Sun were to rise at 4pm or at a different time like noon or midnight. 

"I don't support the idea of the American delegation because I think all our
human activities are linked to the rotation of the Earth first." 

The UK's Department of Trade and Industry (DTI) is co-ordinating its own
response to the American proposal. 

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