* Astronomy

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RE: leap second 2005

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Leap second 2008

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Time Switch

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2005 leap second

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RE: leap second 2005

Blobrana · L

Greenwich Mean Time would become an "irrelevance" if proposals to redefine how time is measured are accepted, an historian at the Royal Observatory Greenwich, UK, has warned.

US scientists want to change the current system, which keeps clocks in synch with solar time by adding a leap second every 18 months or so.

The proposals will be discussed at a meeting in Geneva on Wednesday.

UK scientists believe the meridian's role in timekeeping is under threat.

The Prime Meridian, which runs through Greenwich in south-east London, became the basis for the world's time keeping in 1884 after the first Astronomer Royal, John Flamstead, calculated that the Earth rotated on its axis once every 24 hours.

That discovery meant that time could be defined by the Sun's position relative to a point on the Earth - in this case the meridian running through Greenwich.
It turned out that the Earth's rotation is ever so slightly slowing down. Since 1972 that anomaly was corrected by adding a so-called leap second when necessary.
But according to the Observatory's Curator of Horology - Jonathan Betts - the meridian's role in providing the basis of time keeping across the world is now under threat.
US members of the International Telecommunications Union want to change the current system.

"They want for the first time in history to separate us from the natural rotation of the Earth, which means as the years go by we will increasingly get out of synch with astronomy and the real world. It means in a sense, as far as time keeping is concerned, the meridian line becomes sort of an irrelevance"- Jonathan Betts.

This New Year's Day we'll have an extra second in bed - an extra leap second will be added to the pips at midnight on the first of January.
Although it doesn't make for a luxurious lie-in for most of us - it is important for astronomers such as Dr Robert Massy - who's also at the Royal Observatory.

"Astronomers are people who depend very much on accurate timescales. For example in the field of radio astronomy we need amazingly accurate clocks to ensure that the signals from telescopes on the other side of the world come together and can be aligned correctly, so for us it matters a lot" - Dr Robert Massy.

Without the leap second astronomers would lose track of distant stars and spacecraft. And it would even affect navigation on the Earth. But it's that leap second that some American scientists want to scrap.
Among those upset by the idea is Daniel Gambis who works for the intriguingly named Earth Rotation Service. His job is to decide when to add a leap second. He points out that over time the Earth would gradually get out of synch with the Sun.

"Why can't we just leave things the way they are? 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. And in fact it appears that 90% of our users who need precise timescales are very satisfied by the present procedures" - Jonathan Betts, Royal Observatory Greenwich.

So why do the Americans want to change the system? It's hard to say because despite repeated requests those calling for the changes have been unable to find the time to speak to us.
We've been told that the issue is so controversial in industry circles that the American delegation is lying low. Even the UK's time keeper - the National Physical Laboratory - is keeping quiet. But those who want to keep the leap second say that the American delegation wants to scrap the leap second because it is inconvenient to keep resetting their high precision clocks.
Some think it would be better to add a leap hour every few hundred years. But the Royal Observatory's Jonathan Betts says the US proposal seems "plainly unnatural".

"It really doesn't appeal does it - the idea that we're gradually slipping out of synchronisation with the Earth? And the idea that maybe one day a leap hour could be added is surely a joke. It's going to be thousands of years before such a thing would apply anyway and to allow yourself to get to the stage where you're a whole hour out of synchronisation with the Sun seems to be mad. Why can't we just leave things the way they are?" - Jonathan Betts.

Source BBC.

Blobrana · L

In November 2005, the International Telecommunications Union (ITU) will be discussing a proposal to abolish leap seconds.
The Royal Astronomical Society (RAS) strongly recommends that this proposal should be shelved, and that, before any changes are implemented, there should be a broader, public debate on the future use of these small adjustments to our annual time-keeping.

Our scientific understanding of time has developed over several centuries. Today, scientists recognise that there are two distinct requirements for time-keeping:
• absolute time-keeping, now based on high precision atomic clocks;
• everyday time-keeping, based on the rotation of the Earth (solar time). This is called Coordinated Universal Time (UTC).

Torino meeting

Leap seconds are small adjustments to UTC, which keep ordinary clock time synchronised with the rotation of Earth and thus with the location of the Sun in the sky. They were introduced in 1972 as a reasonable compromise to serve both needs.

There have been 21 leap seconds since 1972 and the next is planned at the end of 2005. Their use is determined by the International Earth Rotation Service, which is sponsored by scientific bodies including the International Astronomical Union.

However, there is now a proposal to abolish leap seconds from December 2007. This proposal will be discussed by the International Telecommunications Union (ITU) at a meeting in Geneva in November 2005.
The proposed change would cause UTC to drift with respect to solar time. If agreed, this would change UTC so that it would serve only precise timing requirements.

The proponents of the change consider leap seconds to be a problem for precision timing applications and thus are seeking solutions. But the present proposal seeks to solve their problem by exporting problems to those who use clock time as a measure of mean solar time (as guaranteed by current international standards). These include astronomers, satellite operators and potentially all who study environmental phenomena related to the rising and setting of Sun.

The idea that clock time follows solar time is deeply embedded in contemporary technical culture through a wealth of literature (text books, web pages etc) and in the skills of working scientists and engineers around the world.

The Society is concerned that this issue has been subject only to a specialist and rather closed debate. There is a clear need for broader debate that involves a wider range of those who will be affected by the proposed change. This should extend outside science and technology – for example, to consider whether civil/legal time should be based on precision time or mean solar time.

The Society strongly recommends that the proposal to abolish leap seconds should be shelved and that the ITU works to promote a broader and public debate.

"This debate should seek a fair solution that serves both needs for time-keeping. There are a lot of skilled people already involved in the debate; we need them to work together to improve current time-keeping for everyone’s benefit and not just for one group" - Mike Hapgood, Secretary of the RAS, who has led the preparation of the Society’s statement.

The International Earth Rotation and Reference Systems Service, located at the Paris Observatory, France, has decided that this year will be one second longer than last year.
A leap second will be added at the end of 31 December 2005 – the first for seven years. The leap second is inserted as the 61st second (23:59:60 UTC) of the last “minute” of the month June or December.

The extra second is needed to keep Coordinated Universal Time (UTC) – currently equivalent to Greenwich Mean Time (GMT) - synchronised with Earth’s rotation. Radio interferometry measurements show that the planet’s spin rate is slowing by about 2 milliseconds per day per century. This gradual slowdown is caused by tides and other effects.

International Atomic Time (TAI) is the continuous, uniform time scale derived from atomic clocks, which are accurate to within one second per three million years. It is the ideal time scale for scientific use, but it is not practical for everyday use since it is not linked to the rotation of the Earth and the actual length of the day. Since it has not been changed since 1958, there is now a 32 second time difference between UTC and TAI.

source

Blobrana · L

Heres a nice graph showing the slowing down of the Earths rotation...

　     2005 . 　　 　　         ―
　　　　2004 . 　　 　　         ―
　　　　2003 . 　　 　　         ―
　　　　2002 . 　　 　　         ―
　　　　2001 . 　　 　　         ―
　　　　2000 . 　　 　　         ―
　22　　1999 . 		   + 1　sec　　　　-32 sec
　　　　1998 . 　　 　　         ―
　21　　1997 . 		   + 1　sec　　　　-31 sec
　20　　1996 . 		   + 1　sec   　 　-30 sec
　　　　1995 . 　　 　　         ―
　19　　1994 . ７. １.      　+ 1　sec   　 　-29 sec
　18　　1993 . ７. １.      　+ 1　sec   　 　-28 sec
　17　　1992 . ７. １.      　+ 1　sec   　 　-27 sec
　16　　1991 . １. １.      　+ 1　sec　　　　-26 sec
　15　　1990 . １. １.      　+ 1　sec　　  　-25 sec
　　　　1989 . 　　 　　         ―
　14　　1988 . １. １.      　+ 1　sec 　　 　-24 sec
　　　　1987 . 　　　 　         ―
　　　　1986 . 　　 　　         ―
　13　　1985 . ７. １.      　+ 1　sec　　　　-23 sec
　  　　1984 . 　　 　　     　  ―
　12　　1983 . ７. １.      　+ 1　sec　　　　-22 sec
　11　　1982 . ７. １.      　+ 1　sec　　　　-21 sec
　10　　1981 . ７. １.      　+ 1　sec　　　　-20 sec
　 9　　1980 . １. １.      　+ 1　sec　　　　-19 sec
　 8　　1979 . １. １.      　+ 1　sec　　　　-18 sec
　 7　　1978 . １. １.      　+ 1　sec　　　　-17 sec
　 6　　1977 . １. １.      　+ 1　sec　　　　-16 sec
　 5　　1976 . １. １.      　+ 1　sec　　　　-15 sec
　 4　　1975 . １. １.      　+ 1　sec　　　　-14 sec
　 3　　1974 . １. １.      　+ 1　sec　　　　-13 sec
　 2　　1973 . １. １.      　+ 1　sec　　　　-12 sec
　 1　　1972 . ７. １.      　+ 1　sec　　　　-11 sec
　 0　　1972 . １. １.       　―  　　　　   　-10 sec

Blobrana · L

To make up for the slowing down of the Earth's rotation, an extra second will be added to 2005.
The “leap second" is the first in seven years and reflects the variation in the Earth's rotation. For the first time since 1998, the International Earth Rotation and Reference Systems Service (IERS) in Paris will add an extra second to get time back in synch.

On Dec. 31, the time will change like this into Jan. 1, 2006:
23h 59m 59s ... 23h 59m 60s ... 00h 00m 00s...

(Normally, the seconds would roll from 59 directly to 00.)

The time will be adjusted to match an atomic clock.
The current standard uses a caesium atom, which vibrates 9,192,631,770 times per second.

The Earth on the other hand changes speed due to tidal forces exerted by the Moon, which is responsible for the gradual long term slowing of the planet's rotation by about 1.5/1000th of a second per century; and other forces such as changes in the season, movement of rock in the molten core etc.
But there are probably other factors that scientists have yet to uncover.
The first leap second was added in 1972, as technology allowed for more accurate timekeeping. One second was added every year between 1972 and 1983 before a slight speedup in the mid-eighties and nineties.

"In 1999 for reasons still unknown, the rotation of the Earth speeded up a bit, so we haven't had to add a second since then" - Tom O'Brian, Chief of the Time and Frequency Division at the U.S. National Institution of Standards and Technology.

Previous
Leap Seconds
12/31/1998
06/30/1997
12/31/1995
06/30/1994
06/30/1993
06/30/1992
12/31/1990
12/31/1989
12/31/1987
06/30/1985
06/30/1983
06/30/1982
06/30/1981
12/31/1979
12/31/1978
12/31/1977
12/31/1976
12/31/1975
12/31/1974
12/31/1973
12/31/1972
06/30/1972