From owner-leapsecs@ROM.USNO.NAVY.MIL Thu Apr 10 22:39:58 2003 Received: from [192.5.41.253] (juno.usno.navy.mil [192.5.41.253]) by santo.ucolick.org (8.11.6+Sun/8.11.6) with SMTP id h3B5dp825177 for ; Thu, 10 Apr 2003 22:39:52 -0700 (PDT) Received: from rom.usno.navy.mil by [192.5.41.253] via smtpd (for santo.ucolick.org [128.114.23.204]) with SMTP; 11 Apr 2003 05:50:04 UT Received: from ROM.USNO.NAVY.MIL (rom.usno.navy.mil [10.1.4.27]) by rom.usno.navy.mil (8.12.8/8.12.5) with ESMTP id h3B5dnTA021707; Fri, 11 Apr 2003 05:39:50 GMT Received: from ROM.USNO.NAVY.MIL by ROM.USNO.NAVY.MIL (LISTSERV-TCP/IP release 1.8e) with spool id 5507 for LEAPSECS@ROM.USNO.NAVY.MIL; Fri, 11 Apr 2003 05:39:49 +0000 Received: from TS-FW.usno.navy.mil (TS-FW.usno.navy.mil [10.1.1.3]) by rom.usno.navy.mil (8.12.8/8.12.5) with SMTP id h3B5dmT8021704 for ; Fri, 11 Apr 2003 05:39:48 GMT Received: from geneva.ucolick.org ([128.114.23.183]) by TS-FW.usno.navy.mil via smtpd (for rom.usno.navy.mil [10.1.4.27]) with SMTP; 11 Apr 2003 05:50:00 UT Received: (from sla@localhost) by geneva.ucolick.org (8.11.6/8.11.2) id h3B5djq01261 for LEAPSECS@ROM.USNO.NAVY.MIL; Thu, 10 Apr 2003 22:39:45 -0700 Date: Thu, 10 Apr 2003 22:39:45 -0700 From: Steve Allen To: Leap Second Discussion List Subject: legal time Message-ID: <20030411053945.GA1257@ucolick.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.1i Sender: owner-leapsecs@ROM.USNO.NAVY.MIL Precedence: list X-Virus: Clean Status: RO X-Status: A Content-Length: 6252 Lines: 123 Hints about ITU-R SRG 7A indicate that UTC might be altered such that leap hours replace leap seconds. In a very broad sense this would satisfy the design that UTC continue to track earth rotation, so in that sense it could continue to merit a name like the other species of "universal" time. The leap hour could be incorporated by omitting the start of daylight saving (summer) time. The necessary legislative amendment for the aberration could be scheduled well in advance. Further, because societies around the world are already forced to endure this sort of legislative meddling with their standard time, it would not even matter much if the leap hour was implemented by different jurisdictions in different years. Presumably the effect of this is to require an omitted daylight change every time that the value of DUT1 accrues to a half-integral hour. If we assume that leap seconds are discontinued real soon and we use the Stephenson and Morrison parabolic fit to delta_T we get the following schedule for legislative acts of omitting daylight changes: DUT1 calendar year grace interval 0.5 hours 2603 600 years 1.5 hours 3152 550 years 2.5 hours 3533 380 years 3.5 hours 3844 310 years 4.5 hours 4113 270 years 5.5 hours 4354 240 years 6.5 hours 4574 220 years The calendar years are, of course, somewhat approximate. I decline to go farther for fear of extrapolating Stephenson & Morrison's rough parabola farther into the future than it goes into the past, and because I don't feel that I share enough with people 100 generations hence to be sure of what they'll want to do. On 2000-07-21 (very early in the history of the LEAPSECS list) Rob Seaman posted a query about the legal issues of disconnecting civil time and solar time. Subscribers can see that note at http://rom.usno.navy.mil/cgi-bin/wa?A2=ind00&L=leapsecs&O=A&F=lf&P=667 I now dig further into the scenarios he mentioned. The proponents of discontinuing leap seconds have given the impression that legal issues are part of the reason for keeping the name UTC and not switching to TAI. They seem to want to be able to discontinue leap seconds in a manner that will avoid involving legislative action. By a rough calculation it appears that changing UTC from leap seconds to leap hours pushes off the need to convince any legislatures to take action for about 600 years. But it really is not as simple as that. Section 10 of the Metrologia paper by Nelson et al. published in 2001 contains material of the sort presented elsewhere by Levine. It notes that the legal basis for time in the UK is (naturally) GMT. It also notes that the legal basis for time in the US is mean solar time of meridians w.r.t. Greenwich. Effectively, both of these societies perform their legal actions based on GMT. So although UTC is, de facto, legal time in many places, it is not legal time de jure in all places. With leap seconds intact, UTC has been able to be used as legal time in the UK and the US because the difference between legal time and UTC is smaller than the discriminatory ability of most human event timing. (For that reason I don't even want to consider whether legal time in the UK and US really means UT2.) Now contemplate DUT1 at finer resolution. According to McCarthy's graph, with about 1 leap second per year being omitted from UTC the value of DUT1 would grow roughly as follows: DUT1 calendar year 30 s 2025 60 s 2050 90 s 2070 120 s 2085 If UTC switches to leap hours then within 50 years there will be a full minute difference between UTC and the legal time currently defined by the UK and the US. When the difference gets larger than that it will begin to be notable in the time stamps of most events such as births, deaths, and traffic accidents. Events such as these which occur around midnight may have large economic significance -- e.g., tax burdens, inheritances, insurance policy expirations. By the time DUT1 reaches 1 minute there will begin to be court cases that challenge the validity of timestamps based on UTC. Expert witnesses will be called in to testify as to how exactly the clocks in a venue were set, and whether that means the event happened on one day or another in the legal time of the jurisdiction. Actually, I expect that the court challenges will happen even sooner. The increased presence of surveillance cameras means that many more events are likely to be recorded with accurate timestamps. Therefore it is conceivable that such court cases could begin to arise when the value of DUT1 exceeds only a few seconds. Court cases such as this will force legislatures to consider the question of the legal timescale. If the ITU-R succeeds in redefining UTC they will not avoid legislative complications. Instead they will guarantee legislative complications within their own lifetimes, and they are aware of this. There are a lot of ways that this process of international professional bodies studying the future of UTC might proceed, and those of us on the outside are at a loss to understand it. The legislative aspects could be approached either before or after making a change to the character of civil time, but upon imagining them the tone of the two seems very different: We see overriding reasons to change legal time to atomic time. We need to set up a series of legislative changes so that in about 30 years (maybe sooner?) we can have a big party where the whole world celebrates a negative leap minute (or less?) and switches civil/legal time from UTC to TAI. or We think you should know that we've stopped adding leap seconds to UTC. That means you have about 10 years to legislate a change in your definition of legal time. If you don't get it done by then, your country becomes lawsuit fodder. How exactly does this international process work? -- Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064 sla@ucolick.org Voice: +1 831 459 3046 http://www.ucolick.org/~sla PGP: 1024/E46978C5 F6 78 D1 10 62 94 8F 2E 49 89 0E FE 26 B4 14 93