M. Warner Losh wrote:
vague rumblings about astronomical software needing to be rewritten,
Unlike Y2K, there is no solid public proposal for astronomers to cost against, but the cost is likely to dwarf Y2K in our community, since algorithms and deployed services would have to change, not just retrofitting two digit years. Folks keep fretting here about retrieving lists of leap seconds autonomously, although no specific use case is proffered about why one needs to use UTC to measure intervals across various and sundry leap second events. On the other hand, astronomers have quite reasonably coded their systems to take advantage of the original (and current) definition of UTC: "GMT may be regarded as the general equivalent of UT." One second of time is 15 seconds of arc on the celestial equator - this is many times greater than the resolution of any O/IR telescope. The proposal really amounts to trading the need to track leap seconds to convert from time-of-day to intervals, for the need to track the equivalent of leap seconds to convert from interval time to time-of-day.
Daylight savings time and time zones prove that society at large has a very high tolerance for variations between the mean solar time at an arbitrary location, maybe hundreds of miles away, and the local time.
This is a static offset. Leap seconds are one mechanism to address a secular drift - a rate, that is, not a constant. Local time - daylight, standard, mean, apparent - has been raised as an issue innumerable times - it has been irrelevant every one of them. We're not talking about mucking with local time, we're talking about subverting the mother of all solar time.
Only specialized users of time would be affected. Who are they and how do we find out the cost of change?
If this is true, you can find out by actually seeking them out, rather than hiding a proposal with worldwide implications away in some squirrelly little bureaucratic committee. However, the suggestion has been implicitly made that everybody is a potential victim of leap seconds - that airplanes will drop from the sky, even though they haven't done so through 23 prior opportunities. That suggestion opens the possibility that "generalized users", i.e., "people" might be affected by civil timekeeping issues in subtle ways. The way to find out the cost of change is to spend some time and money characterizing this. For example, I set my workstation's clock forward eleven years (to match Gregorian calendars) for a couple of years prior to Y2K to provide a platform for our Y2K remediation activities. We set clocks forward at the telescopes and some of them started to track the sky backwards. Surely a Y2K-like inventory could be performed for certain key industries to get a sense for what dependencies might lurk? We've long since established that different countries have different legal civil time standards, e.g., GMT versus UTC. What happens should this discrepancy continue as UTC diverges from GMT? The proposal on the supersecret ITU-R table is to discard an international standard that has been in effect for more than a century and that pervades every aspect of our technical, cultural, legal, economic, etc., world. One might expect somebody might have thought to submit a proposal for a few hundred thousand dollars to conduct a proper pilot study before even beginning to speculate about discarding mean solar time as a basis for civil timekeeping.
These little devices have obviated the need, in many cases, for celestial navigation.
In many cases? That will be comforting to the folks that really need a backup when their GPS goes out. Whatever the solution should be, the one thing it should not be is brittle.
Given that change, the cost benefit analysis that was done in 1972 likely needs updating.
It sounds like we agree on this point.
Seems like a logical leap for leap seconds to follow, if the costs aren't prohibitive. Chances are that one person knows all the users of time that still need DUT1 to be less than 1s.
"Seems like"? "Chances are"? Pick some other random technical issue - say, automobile airbags, standardized educational testing, the lead content of pigment in children's crayons, and so forth and so on. Would "seems like" and "chances are" be phrases you would want to see in a white paper discussing the costs, benefits and risks of these? Oh yeah - that's right. After seven years there is not one single white paper discussing issues related to the decision-making of the ITU-R WP-7A. (And if there were, we presumably would not be able to read it.) There are several thousand professional astronomers in the world and many times this number of amateurs. All of them ultimately care about the subtle concepts underlying the notion of DUT1. It seems bizarre to dismiss their concerns precisely because they might have a more personal interest than some others. It may be naively convenient to assume that the only risks are with poorly designed, non-conforming UTC implementations failing to handle leap seconds - and none with civil time-of-day falling further and further away from actual mean solar time. One might rest easier, however, knowing that any effort whatsoever had been invested in searching for potential risks on both sides.
so maybe some other means of distribution is necessary... And is 100ms really good enough?
Excellent questions. Might I suggest that they be appropriately answered before UTC is removed from life support? Rob Seaman NOAO