Re: Introduction of long term scheduling
On 8 Jan 2007 at 0:15, Tony Finch wrote: > How did you extend the UTC translation back past 1972 if the undelying > clock followed TAI? I assume that beyond some point in the past you say > that the clock times are a representation of UT. However TAI matched UT in > 1958 and between then and 1972 you somehow have to deal with a 10s offset. Formulas for UTC, as actually defined at the time, go back to 1961 here: ftp://maia.usno.navy.mil/ser7/tai-utc.dat It appears the offset was 1.4228180 seconds at the start of this. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: how to reset a clock
On 4 Jan 2007 at 10:53, Peter Bunclark wrote: > Indeed isn't this Rob's ship's chronometer? Captain's log, stardate 30620.1... http://en.wikipedia.org/wiki/Stardate -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: A lurker surfaces
On 2 Jan 2007 at 11:56, Ashley Yakeley wrote: > GPS is TAI. I'm not proposing abandoning TAI for those applications > that need it. It's a few seconds off from TAI, isn't it? It was synchronized to UTC in 1980 (I think), but without subsequent leap seconds, so it's now different from both TAI and UTC. They probably should just have used TAI if they wanted a time scale without leap seconds, rather than ending up creating a different one. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: A lurker surfaces
On 2 Jan 2007 at 11:47, Ashley Yakeley wrote: > The obvious solution is to transmit rubber time on a rubber frequency. Are rubber duckies involved? -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: Introduction of long term scheduling
On 2 Jan 2007 at 19:40, Poul-Henning Kamp wrote: > Has anybody calculated how much energy is required to change > the Earths rotation fast enough to make this rule relevant ? Superman could do it. Or perhaps he could nudge the Earth's rotation just enough to make the length of a mean solar day exactly equal 86,400 SI seconds. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: A lurker surfaces
On 2 Jan 2007 at 12:40, Warner Losh wrote: > The interval math in UTC that's hard today would be significantly > harder with rubber seconds. But it is just software, eh? > > In short, it is an interestingly naive idea that was tried in the > 1960's and failed when there were only dozens of high precision time > users rather than the hundreds of thousands there are today. Actually, "rubber seconds" were what were in use for centuries, as the time calibrated to astronomical observations, with the second defined in terms of the length of a solar day, was what was in use (or, actually, a very rough approximation of it given the lack of accuracy of timepieces in the pre-atomic era). What was tried unsuccessfully in the 1960s was to actually define such timekeeping in a rigorous scientific way allowing conversion to and from atomic time. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: Mechanism to provide tai-utc.dat locally
On 27 Dec 2006 at 20:57, John Cowan wrote: > Very true. And adopting the Egyptian-Roman calendar redefined > the concept of a "month". Somehow civilization survived. Keeping months in sync with phases of the moon apparently turned out to be insufficiently important to civilization to require it as a feature of the calendar. I'm doubtful that keeping clocks in approximate sync with the rising and setting of the sun is likely to be judged equally unimportant, however. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: what time is it, legally?
On 13 Dec 2006 at 21:43, Steve Allen wrote: > http://gauss.gge.unb.ca/papers.pdf/gpsworld.january01.pdf One quibble with that article is that it gives the Global Positioning System as an example of how humanity has been obsessed with knowing what time it is. Actually, GPS arises from our obsession with knowing what *place* we're at; its need for precise time is a mere technical detail of its implementation. (Some of the earlier historical needs for precise time also arose out of navigation, where knowing one's position in space necessitated also knowing something about time.) -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: ADASS poster on UTC
On 28 Oct 2006 at 12:03, John Cowan wrote: > An obvious counterexample is taping TV shows: you don't want to miss > the first or last minute (modulo the presence of commercials). > I go to some trouble to keep my VCR synchronized with NTP time > to the nearest second or two. That's assuming the TV stations / networks broadcast their programs in sync with NTP time, consistently with the official start times of the programs as shown in program guides. In reality, there's some variance; local stations can be somewhat sloppy in their timing, while national networks sometimes play intentional games with making their shows start/end a minute or so early/late to screw up people who channel-surf between their programs and competing networks; also, if there's a sports event earlier in the network's schedule all bets are off as to what time any show might air or whether it will be shown in its entirety. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: 2006 WP-7A meeting summary
On 26 Oct 2006 at 16:01, [EMAIL PROTECTED] wrote: > FYI - this was written for distribution to all interested parties. Why people always feel compelled to use proprietary Microsoftism file formats for things that could be epressed perfectly fine in plain ASCII text I have no idea. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: Comparing Time Scales
On 3 Feb 2006 at 15:37, James Maynard wrote: > Thanks, guys, for your feedback. Here's another iteration. It would seem that PTP is actually counting from 1970-01-01 00:00:00 in TAI rather than UTC; the subsequent values of that scale reflect the full TAI-UTC offset, not just the part of it that occurred after 1970. For instance, the PTP value for 1972-01-01 00:00:00 UTC consists of the number of seconds in the last two (non-leap) years plus 10 seconds. The actual UTC value at 1970-01-01 reflected the variable-length "rubber seconds" of the time, so the TAI-UTC offset then was some fractional value that was less than 10 but greater than 0. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: Risks of change to UTC
On 21 Jan 2006 at 15:15, M. Warner Losh wrote: > For some perspective, we've been using UTC for only ~50 years and the > gregorian calendar for only ~1500 years. I'd anticipate that > something would need to be done about the slowing of the day well > before 4300 years have passed. Actually, that's more like ~400 years for the Gregorian calendar (first instituted in 1582; adopted in different dates in different countries, as late as the 1920s in some). Its predecessor, the Julian calendar, goes back ~2000 years. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: Risks of change to UTC
On 21 Jan 2006 at 10:11, M. Warner Losh wrote: > I maintain that for human activity, there's no need for leap seconds > at all. In each person's lifetime, the accumulated error is on the > order of a few minutes. Over generations, the problems with noon > drifting to 1pm can trivially be solved by moving the timezones that > civilian time uses. What about when that accumulated difference is over 24 hours, so the offset between solar-based time and atomic time is actually on the order of days? Will people be able to deal with a civil time standard that is based on an offset from a "UTC" that says it's Monday when all actual points on Earth have the local date at Saturday or Sunday? Many Web sites (including Wikipedia) use UTC as the standard for date/timestamps; will this be a reasonable thing when this causes the date of postings to be far off from what is being used locally? And when, at some future point, the Gregorian calendar itself needs adjustment to handle the fact that it doesn't get the length of the year precisely correctly (and the length of the year in terms of solar days is changing due to the lengthening of the day, anyway), will this adjustment be done to the UTC standard (why, when it doesn't follow astronomy anyway?), or as an additional offset to local times (which could result in different countries having different dates as in the Julian/Gregorian transition period)? -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: The real problem with leap seconds
On 11 Jan 2006 at 0:08, Tim Shepard wrote: > If humans spread out to other places besides the earth, an > earth-centric time scale might begin to seem somewhat quaint. > Distributing leap second information to a Mars colony seems kind of > silly. As I recall, the NASA Mars missions are using Mars-centric time scales, which include a "Martian second" that has a different length from the SI second in order for the different-length Martian day (called a "Sol") to be subdivided into a familiar 24 "hours" composed of 60 "minutes" each with 60 "seconds". If, however, this Martian second is actually defined as a particular multiple of the SI second, then the use of leap seconds on Mars would ultimately be necessary to account for any future changes in the length of the Martian day. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: interoperability
On 8 Jan 2006 at 15:04, Tom Van Baak wrote: > You cannot divide timekeeping, time dissemination, > into neat stages. In the 1960s if ten labs were told > to offset their phase or frequency it affected only a > handful of people or systems. Today when IERS > announces a leap second, millions of machines, > systems, and people are affected. Thankfully, most > of them handle it OK. Although, even now, the majority of consumer and business equipment is not directly affected in any noticeable way; such machines usually run on a local clock considerably less accurate than an atomic clock, periodically re-synced (perhaps manually, perhaps automatically) to an external time standard. At each such re-syncing, the time may need to be adjusted by a few seconds, or even a few minutes, due to inaccuraccies in the local timepiece, so any leap second that may have occurred since the last syncing will merely result in a 1-second difference in the magnitude of this adjustment, not particularly noticeable to the end users. If some application (e.g., a database) requires a timescale without discontinuities, the application might need to be shut down for a few seconds to perform the time adjustment (whether or not there is a leap second in the mix) in order to prevent data corruption at the moment of the change. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: The real problem with leap seconds
On 7 Jan 2006 at 16:02, Poul-Henning Kamp wrote: > Civil time is in the hands of individual governments, and they > tend to expect their computers to use the same time as the > rest of their country. And, in many countries (including the United States), the legally- defined civil time is the mean solar time at some particular spot, or a fixed or seasonally-variable offset from it. Any use of UTC-based time scales for determining civil time in such places is merely an approximation, currently to within a second, but perhaps varying by greater amounts if some new timekeeping plan is adopted. Once UTC stopped being a sufficiently-close approximation to the solar mean time at the Prime Meridian (with "sufficiently close" possibly being of differing values depending on the particular purpose), it would be necessary to either stop using UTC for determining civil time in such countries, or to change the law to base the civil time on UTC instead of a solar standard. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: Software requirements
On 21 Dec 2005 at 21:33, Poul-Henning Kamp wrote: > I think the difference between you and me as a programmer is that > if you make a mistake, some radio telescope bungles up an observation > or worst case runs against a mechanical end-stop. If I make a > mistake in FreeBSD millions of machines may bungle up things I have > not even dreamt about them doing. > > For Windows the problem is two orders of magnitude higher. I'm a programmer, myself, and I'm pretty confident that all of the computers (Windows or Linux) that I have anything to do with running, maintaining, or writing programs that run on them, will fail to have any adverse effect due to the presence or absence of a leap second at the end of this year or at any other time. This confidence comes from the fact that none of these computers, nor the software running on them, has any need for continuously-accurate real time syncronized with a world standard, something I know from the fact that their system clocks can at times get many seconds (or even minutes) removed from correct time due to their own inaccuracy, requiring pretty big jumps forward or backward each time they are reset to the standard time (which happens automatically at intervals on some machines, and is done manually from time to time on others). While the system clock is inaccurate, all software on the machines continues running with no problem other than that system log timestamps are not exactly correct. This can be annoying when one is trying to track down a network problem by comparing logs on different systems, but it is not life-threatening. Any leap seconds that occur are "lost in the noise" of the adjustments that need to be made to the system clocks every time the time is re-synchronized. I suspect more "real world" computers are in roughly this situation as opposed to being absolutely dependent on being correct to the millisecond or microsecond at all times; the system clocks of practically all computers are just not sufficiently accurate for that. If computers start having an actual atomic clock on board, maybe things will be different. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: a system that fails spectacularly
On 9 Dec 2005 at 10:42, David Harper wrote: > On the other hand, the idea of ISO 9000 compliant Morris dancers is a > very funny one. Presumably, they'd have to standardise the size of > their pig's bladders. There's a Monty Python sketch just waiting to be > written. > > I'm guessing that their level of ISO 9000 compliance falls in inverse > proportion to the amount of beer they drink. As does their likelihood > of observing leap seconds correctly. But if they fail to observe the leap second properly, the timing and synchronization of the dancers will be off, and they might collide catastrophically into one another! We must fix this danger right away! -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: Comments on Civil Time decision tree
On 26 Sep 2005 at 16:09, Poul-Henning Kamp wrote: > Other more laid back parliaments like the Danish have not been able > to find time to revisit the issue since 18xx and still use solar > time at some more or less random coordinate. You mean like the U.S. Congress? http://tycho.usno.navy.mil/260.html "...the standard time of the first zone shall be based on the mean solar time of the sixtieth degree of longitude west from Greenwich..." (and so on for all the other zones) > Imagine for instance that we send a probe out of the solar system > at seriously high speeds and it manages to get as far as 6 light > months away: Under the current UTC rules we would be unable to > upload a leap-second warning and get it there before it is too late. I would suppose that such a space probe would have little need to be synchronized with earthly solar time, and thus might be best off operating on TAI, with any adjustments to UTC for the sake of humans observing it on Earth being done at the Earthly end of things. -- Dan Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: Martian Chronicles
Regarding the discussions of Martian time, more details of the system they're using are here: http://www.giss.nasa.gov/tools/mars24/help/notes.html It seems they've defined Martian "hours", "minutes", and "seconds" as appropriate fractions of the Martian day (which they call a "sol"). This means that there's a "Martian second" which differs from the SI second, and is defined in terms of solar cycles on Mars (and presumably would change its length over time based on any astronomical change in the rotation of Mars). So, maybe what we need is an "Earth second" also based on solar cycles (as the second always was prior to the middle of the 20th century), distinct from the scientific second based on atomic clocks? -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Re: new beginning
On 5 Aug 2005 at 10:16, Mark Calabretta wrote: > The fiction that there are 86400 "seconds" in a solar day is part of > the problem - noone uses the word "second" in this context. Currently > there are about 86400.003 seconds in a mean solar day but we use leap > seconds so that we can carry on pretending that there are only 86400. > Eventually when there are 86401 seconds in a mean solar day, or > probably well before, we'll simply have to stop pretending. Actually, I'd say that more people use the word "second" in this context than do in the scientifically accurate context of the SI definition. To the "man/woman on the street", a second is 1/60 of a minute, a minute is 1/60 of an hour, and an hour is 1/24 of a day, just as these units were originally defined before scientists got more precise about it. And a day is defined in terms of the relationship of the Sun and the Earth; even if this mythical non- scientific member of the public doesn't know the technical astronomical details of "mean solar time" and so on, he/she knows that the sun rises and sets exactly once within this time unit. So the solar definition of "second" is actually more in line with how the average person regards the unit than the SI definition. -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
Time after Time
I sure hope that the future of mankind's timekeeping systems doesn't get decided by an Internet flame war between contending groups of geeks... As I see it, the dispute comes from the fact that people want two different, irreconcilable types of "time", time of day (earth/solar angle) and constant interval time. Traditionally (over all of human history), civil time has always related in some way to solar-angle time, originally directly, and now in a complex, artificial way with confusing politically-imposed irregularities such as daylight saving time and wildly gerrymandered time zones. It still does relate to solar time, however, with the local clock time at a given point on Earth at a particular time of year generally fixed at a constant increment from solar mean time for that spot (but sometimes changing to a different increment for part of the year). There's no prospect that eventually, due to discrepancies in the system, noon will come when it's dark (except perhaps very near the north or south poles). Some of the proposals, however, seek to decouple civil time altogether from solar time, an unprecedented step which would possibly lead to day and night being completely reversed; any "leap hours" that prevented this would, if ever implemented, be even more traumatic than leap seconds are now. In addition to being historically unprecedented, such a move would be illegal in the United States and some other countries, which have laws explicitly defining their time zones based on solar mean time, unless such laws were changed. Now, if a time standard is to be defined based solely on constant SI seconds, with no reference to astronomy, then why even include all the irregularities of the Gregorian Calendar, with its leap year schedule designed to keep in sync with the Earth's revolutions? It really makes no sense that TAI includes days, years, and so on at all, and this will seem particularly senseless when the current date by TAI is a day or more removed from Earth-rotational time, as will happen in a few millennia. What is really needed is two different time standards: a fixed- interval standard consisting solely of a count of SI seconds since an epoch (no need for minutes, hours, days, months, and years), and a civil-time standard that attempts, as best as is practical, to track the (slightly uneven) motions of the Earth. When other planets are settled, they'll need their own local time standards too (NASA is already doing this for Mars). -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/
