Andrew Yee
December 23rd 05, 03:37 PM
Royal Astronomical Society Press Notice
London, U.K.
CONTACTS:
Dr. Mike Hapgood
RAS Secretary
Tel.: +44 (0)789-9908 780
John McFarland
Armagh Observatory
College Hill
Armagh
BT61 9DG
Tel.: +44 (0)28-3751-2962
Prof. Mark Bailey
Armagh Observatory (see above)
Tel: +44 (0)28-3752-2928
Friday, 23 December 2005
New Year to Arrive One Second Late
Contributed by Peter Bond
The arrival of 2006 will be delayed by one second, the first time a leap
second has been added for seven years. Owing to the gradual slowing down
of the Earth's rotation, the International Earth Rotation and Reference
Systems Service, based at the Paris Observatory, has announced that 2005
will contain an extra second.
The required leap second will be added at the end of 31st December, thus
delaying the arrival of 2006 by one second. Although this will be the
23rd such leap second to be added since its introduction at the end of
June 1972, this year's leap second will be the first for seven years.
Our normal civil, or clock time, is based on Greenwich Mean Time (GMT),
the world standard since 1884, which is tied to when the Sun arrives due
south at the Greenwich Meridian, the zero line of longitude. The
resulting 'Universal Time' is based, as has always been the case, on the
rotation of the Earth on its axis.
However, the speed of the Earth's rotation is continually changing: partly
due to varying weather patterns and geological disturbances, but more
importantly due to the friction of tides raised by the Sun and Moon, which
cause a systematic lengthening of the day.
In fact, the day is now about 2 milliseconds longer than it was a couple
of hundred years ago. As a result, leap seconds will always be needed if
we are to keep 'clock time' and 'Sun time' in step.
However, the International Telecommunications Union has recently proposed
that the practice of inserting leap seconds should be abolished. This
would remove the difficulty of updating communication and navigation
systems following a change that ultimately depends on the unpredictable
slowing of the Earth's rotation.
But the proposal is subject to the law of unintended consequences. Quite
apart from professional scientists, such as astronomers, who might be
adversely affected by such a change, over hundreds of years the civil time
would no longer coincide, even approximately, with the 'Sun time'
traditionally shown on a sundial. Even over a few decades, when the error
might grow up to a half a minute or so, one can imagine the arguments that
lawyers and insurance companies might have about whether an event had
occurred just before or just after midnight; and in today's modern
electronic era differences of seconds between different people's
interpretation of the correct time might sometimes lead to dispute!
The Royal Astronomical Society has recommended that any decision on such a
fundamental change in the way we record time should not be left to a
single professional body, but should instead follow a much wider, more
informed public debate.
FURTHER INFORMATION
* Leap second talks are postponed (BBC Science/Nature web site)
http://news.bbc.co.uk/1/hi/sci/tech/4420084.stm
* Leap seconds discussion at US Naval Observatory
http://rom.usno.navy.mil/archives/leapsecs.html
* Steve Allen's bibliographic gathering of references on leap seconds
http://www.ucolick.org/~sla/leapsecs/onlinebib.html
* Marcus Kuhn's leap seconds site at Cambridge
http://www.cl.cam.ac.uk/~mgk25/time/leap/
* The UTC Problem and its Solutions, presentation by Pat Wallace
http://www.ien.it/luc/cesio/itu/wallace.pdf
* Time Bandits, article by Wendy Grossman
http://www.theinquirer.net/?article=25190
* Detailed article by proponents of change
http://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf
*****
Observatoire de Paris
Paris, France
Press Contact:
Brigitte BOURDON
Observatoire de Paris, Directrice de la communication
Tél: 33 1 40 51 21 55
Scientific Contact:
Daniel GAMBIS
IERS, Observatoire de Paris, SYRTE
Tél: 33 1 40 51 22 29
Fax: 33 1 40 51 22 91
David VALAT
LNE, Observatoire de Paris, SYRTE
Tél: 33 1 40 51 22 15
Fax: 33 1 43 25 55 42
Philip TUCKEY
Directeur, Observatoire de Paris, SYRTE
Tél: 33 1 40 51 22 46
Fax: 33 1 43 25 55 42
21 December 2005
An extra second in 2005
January 1, 2006, at 1 hour in the morning, it will be necessary to delay
watches by just a second. Very exceptionally, the minute between midnight
59 minutes and 1 hour will last one second more than normal, that is 61
seconds instead of 60. Any clock which will count as usual the 60 seconds
for this minute will thus post "1 hour" with one second in advance, and
will have to be corrected, at least for those who need the standard time
with a second accuracy.
In the scale of international time "UTC", this additional second, will
take place on December 31, 2005, just before midnight. The scientists thus
tend to consider that it belongs to 2005. But in France, because of the
time shift compared to UTC, of one hour in winter (+1 H), it will arrive
actually at 1 a.m. on January 1... 2006.
It is at Paris Observatory that is played this second. Indeed, the
department "Reference Frames for Time and Space" -- SYRTE, by its
activities in the measurement of the Earth rotation and the metrology of
time, plays a key role in this event.
The rotation of the Earth on itself which determines the passage of days
and nights, slows down on the long term, because mainly of the effects of
luni-solar attraction. Moreover, our planet is disturbed by its internal
components (core, mantle) and external (atmosphere, oceans).
However, time is measured today by means insensitive to Earth moods,
thanks to 250 atomic clocks belonging to several countries of the globe,
including 25 in France. Together, they allow to calculate the Coordinated
Universal Time -- UTC [See Note 1].
And the UTC is so regular that it appears quickly a shift between it and
the time of days and nights determined by the rotation of the Earth on
itself.
This shift which can be awkward for certain applications, an international
agreement signed in 1972 stipulates that the difference between the two
should never exceed a second [2]. This is the reason why additional
seconds were created: when the shift between UTC and Earth rotation time
approaches one second, the insertion of a "leap" second in UTC allows to
readjust the two scales.
Paris Observatory ensures scientific services entrusted by national and
international organizations. It is for this reason that a component of the
"International Earth Rotation Service" -- IERS, located at SYRTE, is
responsible for the prediction and the advertisement of these leap
seconds. This decision is then implemented by the international and
national authorities responsible for the diffusion of time.
For France, the LNE-SYRTE [3] is in charge of this mission. This other
component of the SYRTE makes the Coordinated Universal Time of the
Observatory of Paris -- UTC(OP). This reference of high degree of accuracy
is used by the speaking clock of France Telecom, lodged at the Observatory
of Paris, to diffuse French legal time; one can listen to it by composing
the 36 99. The legal time based on UTC(OP) is also diffused in a
transparent way by encoding on the radio carrier wave of France Inter, so
as to be used continuously by laboratories, industrials, communities, etc,
everywhere in Metropolitan France [4].
International discussions in progress since several years could lead to a
modification of this system. UTC would become dissociated from the Earth
rotation and we would not have to add leap seconds any more.
NOTES:
[1] The International Office of Weights and Measures -- BIPM,
international organization located in Sevres, is in charge of the
calculation of UTC. It is a scale of time said on "paper", known with a
delay of up to 6 weeks. Any country needing a powerful metrology of time
must carry out its own approximate version of UTC in real time. For
France, this reference is the Coordinated Universal Time of the
Observatory of Paris -- UTC(OP).
[2] Until 1960, the unit of second was defined as the 864002th fraction of
one solar day, averaged over the year 1900. Today it is defined as 9 192
631 770 periods of radiation corresponding to the transition between two
hyperfine levels from the fundamental state of cesium 133.
[3] A contract between the National Laboratory of Metrology and Tests --
LNE, the Observatory of Paris and CNRS created, within the SYRTE, the
LNE-SYRTE, laboratory charged to carry out and broadcast the national
references for metrology of time and frequencies.
[4] A partnership between the French Office of the Clock Industry and
Microtechniques -- CFHM and the LNE manages this means of diffusion of
legal time.
RELATED LINKS:
* Reference Frames for Time and Space -- SYRTE
http://www.obspm.fr/syrte
* International Earth Rotation Service -- IERS
http://hpiers.obspm.fr/
* International Office of Weights and Measures -- BIPM
http://www.bipm.fr/en/home/
IMAGE CAPTIONS:
[Figure 1:
http://www.obspm.fr/actual/nouvelle/dec05/second-f1.jpg (12KB)]
Long-term slow-down of the Earth rotation since 1830 (in red). The pink
curve represents the influence of the fluid core of the Earth.
© Daniel Gambis, SYRTE-Observatoire de Paris
[Figure 2:
http://www.obspm.fr/actual/nouvelle/dec05/second-f2.jpg (30KB)]
The control room of the LNE-SYRTE
The speaking clock which diffuses French legal time stands together with
diffusion systems ten million times more precise. The latter, exploiting
the performances of the atomic clocks, are used in the scientific
applications of the metrology of time.
© SYRTE-Observatoire de Paris
London, U.K.
CONTACTS:
Dr. Mike Hapgood
RAS Secretary
Tel.: +44 (0)789-9908 780
John McFarland
Armagh Observatory
College Hill
Armagh
BT61 9DG
Tel.: +44 (0)28-3751-2962
Prof. Mark Bailey
Armagh Observatory (see above)
Tel: +44 (0)28-3752-2928
Friday, 23 December 2005
New Year to Arrive One Second Late
Contributed by Peter Bond
The arrival of 2006 will be delayed by one second, the first time a leap
second has been added for seven years. Owing to the gradual slowing down
of the Earth's rotation, the International Earth Rotation and Reference
Systems Service, based at the Paris Observatory, has announced that 2005
will contain an extra second.
The required leap second will be added at the end of 31st December, thus
delaying the arrival of 2006 by one second. Although this will be the
23rd such leap second to be added since its introduction at the end of
June 1972, this year's leap second will be the first for seven years.
Our normal civil, or clock time, is based on Greenwich Mean Time (GMT),
the world standard since 1884, which is tied to when the Sun arrives due
south at the Greenwich Meridian, the zero line of longitude. The
resulting 'Universal Time' is based, as has always been the case, on the
rotation of the Earth on its axis.
However, the speed of the Earth's rotation is continually changing: partly
due to varying weather patterns and geological disturbances, but more
importantly due to the friction of tides raised by the Sun and Moon, which
cause a systematic lengthening of the day.
In fact, the day is now about 2 milliseconds longer than it was a couple
of hundred years ago. As a result, leap seconds will always be needed if
we are to keep 'clock time' and 'Sun time' in step.
However, the International Telecommunications Union has recently proposed
that the practice of inserting leap seconds should be abolished. This
would remove the difficulty of updating communication and navigation
systems following a change that ultimately depends on the unpredictable
slowing of the Earth's rotation.
But the proposal is subject to the law of unintended consequences. Quite
apart from professional scientists, such as astronomers, who might be
adversely affected by such a change, over hundreds of years the civil time
would no longer coincide, even approximately, with the 'Sun time'
traditionally shown on a sundial. Even over a few decades, when the error
might grow up to a half a minute or so, one can imagine the arguments that
lawyers and insurance companies might have about whether an event had
occurred just before or just after midnight; and in today's modern
electronic era differences of seconds between different people's
interpretation of the correct time might sometimes lead to dispute!
The Royal Astronomical Society has recommended that any decision on such a
fundamental change in the way we record time should not be left to a
single professional body, but should instead follow a much wider, more
informed public debate.
FURTHER INFORMATION
* Leap second talks are postponed (BBC Science/Nature web site)
http://news.bbc.co.uk/1/hi/sci/tech/4420084.stm
* Leap seconds discussion at US Naval Observatory
http://rom.usno.navy.mil/archives/leapsecs.html
* Steve Allen's bibliographic gathering of references on leap seconds
http://www.ucolick.org/~sla/leapsecs/onlinebib.html
* Marcus Kuhn's leap seconds site at Cambridge
http://www.cl.cam.ac.uk/~mgk25/time/leap/
* The UTC Problem and its Solutions, presentation by Pat Wallace
http://www.ien.it/luc/cesio/itu/wallace.pdf
* Time Bandits, article by Wendy Grossman
http://www.theinquirer.net/?article=25190
* Detailed article by proponents of change
http://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf
*****
Observatoire de Paris
Paris, France
Press Contact:
Brigitte BOURDON
Observatoire de Paris, Directrice de la communication
Tél: 33 1 40 51 21 55
Scientific Contact:
Daniel GAMBIS
IERS, Observatoire de Paris, SYRTE
Tél: 33 1 40 51 22 29
Fax: 33 1 40 51 22 91
David VALAT
LNE, Observatoire de Paris, SYRTE
Tél: 33 1 40 51 22 15
Fax: 33 1 43 25 55 42
Philip TUCKEY
Directeur, Observatoire de Paris, SYRTE
Tél: 33 1 40 51 22 46
Fax: 33 1 43 25 55 42
21 December 2005
An extra second in 2005
January 1, 2006, at 1 hour in the morning, it will be necessary to delay
watches by just a second. Very exceptionally, the minute between midnight
59 minutes and 1 hour will last one second more than normal, that is 61
seconds instead of 60. Any clock which will count as usual the 60 seconds
for this minute will thus post "1 hour" with one second in advance, and
will have to be corrected, at least for those who need the standard time
with a second accuracy.
In the scale of international time "UTC", this additional second, will
take place on December 31, 2005, just before midnight. The scientists thus
tend to consider that it belongs to 2005. But in France, because of the
time shift compared to UTC, of one hour in winter (+1 H), it will arrive
actually at 1 a.m. on January 1... 2006.
It is at Paris Observatory that is played this second. Indeed, the
department "Reference Frames for Time and Space" -- SYRTE, by its
activities in the measurement of the Earth rotation and the metrology of
time, plays a key role in this event.
The rotation of the Earth on itself which determines the passage of days
and nights, slows down on the long term, because mainly of the effects of
luni-solar attraction. Moreover, our planet is disturbed by its internal
components (core, mantle) and external (atmosphere, oceans).
However, time is measured today by means insensitive to Earth moods,
thanks to 250 atomic clocks belonging to several countries of the globe,
including 25 in France. Together, they allow to calculate the Coordinated
Universal Time -- UTC [See Note 1].
And the UTC is so regular that it appears quickly a shift between it and
the time of days and nights determined by the rotation of the Earth on
itself.
This shift which can be awkward for certain applications, an international
agreement signed in 1972 stipulates that the difference between the two
should never exceed a second [2]. This is the reason why additional
seconds were created: when the shift between UTC and Earth rotation time
approaches one second, the insertion of a "leap" second in UTC allows to
readjust the two scales.
Paris Observatory ensures scientific services entrusted by national and
international organizations. It is for this reason that a component of the
"International Earth Rotation Service" -- IERS, located at SYRTE, is
responsible for the prediction and the advertisement of these leap
seconds. This decision is then implemented by the international and
national authorities responsible for the diffusion of time.
For France, the LNE-SYRTE [3] is in charge of this mission. This other
component of the SYRTE makes the Coordinated Universal Time of the
Observatory of Paris -- UTC(OP). This reference of high degree of accuracy
is used by the speaking clock of France Telecom, lodged at the Observatory
of Paris, to diffuse French legal time; one can listen to it by composing
the 36 99. The legal time based on UTC(OP) is also diffused in a
transparent way by encoding on the radio carrier wave of France Inter, so
as to be used continuously by laboratories, industrials, communities, etc,
everywhere in Metropolitan France [4].
International discussions in progress since several years could lead to a
modification of this system. UTC would become dissociated from the Earth
rotation and we would not have to add leap seconds any more.
NOTES:
[1] The International Office of Weights and Measures -- BIPM,
international organization located in Sevres, is in charge of the
calculation of UTC. It is a scale of time said on "paper", known with a
delay of up to 6 weeks. Any country needing a powerful metrology of time
must carry out its own approximate version of UTC in real time. For
France, this reference is the Coordinated Universal Time of the
Observatory of Paris -- UTC(OP).
[2] Until 1960, the unit of second was defined as the 864002th fraction of
one solar day, averaged over the year 1900. Today it is defined as 9 192
631 770 periods of radiation corresponding to the transition between two
hyperfine levels from the fundamental state of cesium 133.
[3] A contract between the National Laboratory of Metrology and Tests --
LNE, the Observatory of Paris and CNRS created, within the SYRTE, the
LNE-SYRTE, laboratory charged to carry out and broadcast the national
references for metrology of time and frequencies.
[4] A partnership between the French Office of the Clock Industry and
Microtechniques -- CFHM and the LNE manages this means of diffusion of
legal time.
RELATED LINKS:
* Reference Frames for Time and Space -- SYRTE
http://www.obspm.fr/syrte
* International Earth Rotation Service -- IERS
http://hpiers.obspm.fr/
* International Office of Weights and Measures -- BIPM
http://www.bipm.fr/en/home/
IMAGE CAPTIONS:
[Figure 1:
http://www.obspm.fr/actual/nouvelle/dec05/second-f1.jpg (12KB)]
Long-term slow-down of the Earth rotation since 1830 (in red). The pink
curve represents the influence of the fluid core of the Earth.
© Daniel Gambis, SYRTE-Observatoire de Paris
[Figure 2:
http://www.obspm.fr/actual/nouvelle/dec05/second-f2.jpg (30KB)]
The control room of the LNE-SYRTE
The speaking clock which diffuses French legal time stands together with
diffusion systems ten million times more precise. The latter, exploiting
the performances of the atomic clocks, are used in the scientific
applications of the metrology of time.
© SYRTE-Observatoire de Paris