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 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: 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 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: 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: 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: 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: 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: 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: 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/
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/
