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Dear Colleague,

It has been 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.

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?

B. Would you be in favor of such a proposal?

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 [2,000] to

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.

Demetrios Matsakis, Director, Time Service Department, U. S. Naval Observatory
Nov 16, 1999