Royal Astronomical Society statement on the proposed abolition ofleap seconds (Forwarded)

Royal Astronomical Society Press Notice
London, U.K.

CONTACT DETAILS

Dr. Mike Hapgood
Rutherford Appleton Laboratory-CCLRC
Tel.: +44 (0)789-9908 780
E-mail: M.Hapgood @ rl.ac.uk

Tuesday, 20 September 2005

RAS PN05/41

RAS STATEMENT ON THE PROPOSED ABOLITION OF LEAP SECONDS
Contributed by Peter Bond

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).

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," said Mike Hapgood, Secretary of the RAS, who has led the
preparation of the Society's statement. "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."

NOTES FOR EDITORS

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 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.

FURTHER INFORMATION

* 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/...leapsecond.pdf

For reactions to this press release see

http://www.telegraph.co.uk/news/main...22/ixhome.html

http://news.scotsman.com/scitech.cfm?id=1975362005

http://news.moneycentral.msn.com/pro...1&ID=51307 87

http://www.innovations-report.de/htm...cht-49533.html