Does "another correction for sundials", as Jean Meeus writes, also means an
extra shift in the system wintertime/summertime?.
What is the concequence for our daily live?
Because of my interests I agree with Jean Meeus.
Keep the leap second, no leap hour.
Best wishes, Fer.
Fer J. de Vries
De Zonnewijzerkring
mailto:[EMAIL PROTECTED]
http://www.de-zonnewijzerkring.nl
Eindhoven, Netherlands
lat. 51:30 N long. 5:30 E
----- Original Message -----
From: "Frank King" <[EMAIL PROTECTED]>
To: <sundial@rrz.uni-koeln.de>
Cc: "Jonathan" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; "Frank
King" <[EMAIL PROTECTED]>
Sent: Sunday, July 10, 2005 10:38 PM
Subject: Save the Leap Second
Dear Diallists,
I wonder whether anyone shares my thoughts about the current
proposals to make serious changes to UTC. There seems to be
every chance that the Leap Second procedure will be abolished.
At present UTC is kept within 0.9s of UT1 by means of the
occasional leap second. The proposal is to let these times
differ by up to an hour. This would introduce a major extra
correction when comparing sundial time and clock time.
[ UT1 is, of course, the hypothetical time by the mean
sun on the Greenwich Meridian. Accordingly, UT1 is
the time of greatest interest to diallists. UTC is
the base time for Civil Time throughout the world and
is what clocks are set to in the UK in Winter.
It is a major blessing to diallists and anyone who uses
astronomical tables that UTC and UT1 are guaranteed the
same to within one second.]
The outline of the proposals can be seen at:
http://www.ucolick.org/~sla/leapsecs/gambis.html
Be warned. Pour a stiff drink before reading this!
The proposals come from the International Telecommunications
Union, ITU. Their Working Party 7A, or WP-7A, proposes:
1 - Maintenance of a time scale called UTC.
2 - Suppression of the leap seconds adjustments which
maintains UTC close to UT1, a time scale based on the
Earth's rotation (currently UT1-UTC < .9 s)
3 - The difference of UT1 from UTC should not exceed 1 hour.
4 - The change should take effect at 21 December 2007, 00:00 UTC
We are told helpfully:
If your activity is affected by the content of the US proposal
which will be discussed in November 2005 at the WP-7A, you are
urged to react.
Well our activity will certainly be affected. In my view, we
should indeed react.
My view is not of great consequence of course but take a look
at what Jean Meeus says, epecially Point (6) about sundials, in
his message to Daniel Gambis of the IERS [to whom representations
should be made]:
------- Forwarded Message
Date: Fri, 8 Jul 2005 02:47:00 -0400
From: Jean Meeus <[EMAIL PROTECTED]>
Subject: About UTC
Sender: Jean Meeus <[EMAIL PROTECTED]>
To: Daniel Gambis <[EMAIL PROTECTED]>
...
Acceptance of the US proposal would be a disaster for classical
astronomy, and below I mention several inconveniences. The proposal
to adopt the change on 21 December 2007 is a dirty trick: for me,
it is evident that this date has been chosen in order that no leap
second could be introduced at the end of December 2007.
(1) A first inconvenience of the change would be that the mean Sun
would no longer transit the meridian of Greenwich at 12:00,
"official time", and this would be the end of a long tradition.
Very regrettable!
(2) Acceptance of the change would result in three separate uniform
time scales running "parallel" to each other, indeed a ridiculous
situation. Presently, we already have the Dynamical Time and the
Atomic Time (TAI) which differ by a constant value, 32.184 seconds.
If the US proposal is accepted, then we would have a third parallel
time scale, the (new) UTC. There is no need to have a proliferation
of those parallel time scales.
(3) As long as the difference UT-UTC remains smaller than 0.9 second,
this difference can be neglected for many applications where no
extremely high accuracy is needed. This the case for the instants
given for occultations, the phenomena of the satellites of Jupiter,
etc., as published in various astronomical almanacs. These instants
are given in UT, and we can simply use the time given by the radio
signals which are in UTC, and consider them to be equal to UT. That
would no longer be the case if a new definition of UTC is accepted.
(4) A newly defined UTC would be a problem when constructing long lists
of astronomical phenomena such as lunar eclipses or transits of
Mercury and Venus. Suppose we want to construct such a list for
the years 1000 to 3000. What time scale should we use? If we
choose UT, then times given for, say, the year 2500 would not be
consistent with the official time, which will be the (new) UTC.
If, instead, we choose UTC, then there would be another problem:
of course for years before 1900, UTC would be meaningless, as in
those years there were no leap seconds and even no time signals!
And events taking place in, say, 1975 and 2500 would not be
comparable, because the UTC used in 1975 would not be the new UTC.
(5) It is proposed that "The difference of UT1 from UTC should not
exceed 1 hour." This means that a leap *hour* should be introduced
when the difference between UT and UTC becomes too large, which would
be the case somewhere between the years 2800 and 3200. Of course the
exact year is not yet known presently, as it depends on the slowing
down of the Earth's rotation.
Consider, for instance, the transit of Venus of 14 June 2984. First
exterior contact (for the Earth's center) will take place at 10:10:23
Dynamical Time. This will be 10:09 UTC if the US proposal is
accepted.
However, if the leap hour is introduced before A.D. 2984, then the
instant would become 09:09 UTC. Consequently, presently we don't
know
whether the transit will begin at 09:09 or at 10:09 in the proposed
UTC scale, and hence it is not possible to create a long list of
events with the instants expressed in UTC.
(6) Finally, for sundials, too, the situation would be complicated.
Presently, to convert true solar time (as given by a sundial) to
"official" time, we have to take into consideration: the longitude
difference with Greenwich, the equation of time, and the fact that
we use or not the "summer" time. But if the US proposal is accepted,
a further correction would be needed: the difference between UT and
UTC, a difference that is now negligible, but that will gradually
increase over the years if the US proposal is accepted.
Finally, I don't understand why the ITU and the people of GPS insist to
suppress the leap seconds. Are they really unable, notwithstanding the
modern technique of the 21th century, to handle this "problem"? Should
astronomy suffer because those guys cannot handle the leap seconds
easily?
Jean Meeus (Belgium)
------- End of Forwarded Message
For further details see:
http://www.cl.cam.ac.uk/~mgk25/time/leap/
http://www.ucolick.org/~sla/leapsecs/
I regard all this as bad news. Quite apart from anything else,
having a leap hour some time in the future seems like building
up a problem that will make the Y2K nonsense seem a trivium.
What do others think? Should we take to the streets?
Frank King
Cambridge, U.K.
-
-
