[fitsbits] Re: leap second alert

[William Thompson]

seaman at noao.edu (Rob Seaman) writes:

>We had an interesting inquiry that deserves a wider distribution.
>An astronomer with a friend at the NIST forwarded this to an NOAO
>staff member who forwarded it to me.  Now it's in your lap, too.

>    > As you know, Coordinated Universal Time (UTC) is derived from cesium
>    > clocks with the occasional addition of leap seconds. These leap seconds
>    > guarantee that the magnitude of UTC-UT1 does not exceed 1 s.
>    > 
>    > Managing leap seconds is an administrative headache, and there have
>    > been proposals for some time to abandon using them. If this were done,
>    > the difference between UTC and UT1 would grow without bound. Currently,
>    > the rate of divergence is about 1 minute per century, and this rate is
>    > projected to increase as the Earth continues to slow down.
>    > 
>    > Assuming this were done, would the lives of astronomers be made more
>    > difficult?  If astronomers have to incorporate a UT1 correction in any
>    > case, does it matter how big it is? If they currently use this
>    > correction, how accurately do they need to know it?
>    > 
>    > Thanks for your assistance.
>    > 
>    > Judah Levine

	(rest deleted)

I'm also concerned about this.  Not very long ago, I received a questionaire
from the USNO concerning this matter.  Since the questionaire includes the
statement "feel free to forward this eamil directly", and since the question
has come up in this group, I'm including it below.

Personally, I have many reservations about this proposal, which I have
communicated to the address below.  The simplest reservation is, if UTC-TAI
were to remain at a fixed value, why have UTC at all?  Why not simply use TAI?

I also don't see what the big deal is.  One of my responsibilities is keeping
track of the addition of new leap seconds, and it's really a simple, minor
task.  It's hard to see what's driving this proposal.

William Thompson

===============================================================================
Date: Tue, 9 Nov 1999 02:06:16 +0000 (UTC)
From: "Demetrios N. Matsakis" <dnm at orion.usno.navy.mil>
To: ptw at star.rl.ac.uk
Subject: Leap Second Questinnaire

Dear Project Manager or Scientist,
 
It is being proposed to change the definition of Coordinated Universal
Time (UTC) regarding the insertion of leap-seconds, possibly even
eliminating their use.  Leap seconds are introduced so as to keep UTC
synchronized (within 0.9 s) to the time scale determined from the
Earth's rotation, however many practical problems result from their
implementation.
 
Should no new leap seconds be inserted, solar time will diverge from
atomic time at the rate of about 2 seconds every 3 years, and after
about a century |UT1-UTC| would exceed 1 minute.  Although no
fundamental problems are anticipated, it is very likely that Y2K-like
problems may result in software that assumes UT1=UTC, or |UT1-UTC|< some
value, or whose input/output records use a field size that can only 
accommodate |UT1-UTC| values up to one second.
 
To gather information, an URSI Commission J Working Group was formed,
consisting of Don Backer, Wim. N. Brouw, Barry Clark, Irwin Shapiro,
Ir. E. Van Lil, and myself.
 
We would like to ask you to consult with the members of your institute
who currently deal with UT1-UTC, and give us a considered response to
the following two questions:
 
A. If the appropriate international bodies decide to eliminate the
insertion of new leap seconds, would you foresee any practical problems
for your institution/instrument/observations?
 
     no  ____
 
  *  yes ___
 
  *  possibly ____
 
     (* please explain any known or possible problems)
 
B. Would you be in favor of such a proposal?
 
     yes ____
 
     no  ____
 
     indifferent ___

     have better idea ___
 
     (feel free to comment)

C. Is there anyone else you would recommend we contact?
    (feel free to forward this eamil directly)
 
I would appreciate your assistance, and a response by January 15 to
dnm at orion.usno.navy.mil.
 
I am attaching a list of institutions and persons contacted, except
for 931 institutions whose emails were obtained from the AAS. I would
like to apologize to anyone contacted twice, but also appreciate it if
you would forward this email to anyone we have missed.  Also, if you
are an URSI Commission J national chair, we would appreciate your
forwarding this email to your complete membership and in particular to
the directors of observatories.

Sincerely,
 
Demetrios Matsakis
________________________________________________________________________
Dr. Demetrios N. Matsakis            Director, Time Service Department
(202) 762-1587  DSN 762-1587         U. S. Naval Observatory
FAX (202) 762-1511                   3450 Massachusetts Avenue NW 
dnm at orion.usno.navy.mil              Washington DC, USA  20392-5420
________________________________________________________________________

List of Recipient Email Addresses

	(128 addresses deleted)

(In addition to the above, 931 institutions which have provided
email contacts to the AAS are being contacted.)