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Avoiding the Leap Second
On 31 mei, 09:04, Quadibloc wrote:
Paul Schlyter wrote: Since I am proposing lengthening the second *only in those years with leap seconds*, obviously I would not seriously propose that the ohm, volt, et cetera be different in those years too. That would be insanity, and rest assured I suggest no such thing. John Savard But you'd have no choice, what does a frequency counter (piece of electronic equipment show? Pulses per second (Hertz). And these may wel be calibrated against NIST, and some measure in pico seconds, quite a bit of error would show! Now endless arguments would be created if it was your new second or the real second or whatever, The wavelength scale on your radio, basically all other physics constants, you car's km/hour or miles/hour... what not! I say: Forget it:-) |
#12
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Avoiding the Leap Second
On 2007-05-31, Quadibloc wrote:
There are also some hidden assumptions: these are - Except for TV stations, that use cesium and rubidium clocks to maintain their frequency on track (and they wouldn't need to do anything, because frequency would still be measured in terms of the SI second, not the second of civil time) nobody else in the private sector uses anything better than a quartz crystal timer. These are accurate to about five seconds a year, so changing the length of a second with an impact of *one* second a year isn't going to impact the real-time clocks in computers or in Internet routers. A couple of points here. TV stations are not by any means the only people with requirements for precision timekeeping, and in any case TV transmitters don't use atomic clocks in the manner you suggest. Secondly, quartz isn't nearly as accurate as you suggest. A 32.768kHz crystal typically has a quoted accuracy of 10ppm. According to my HP-21 that works out at 315 s a year. That's over five _minutes_. Mechanical clocks are capable of far better accuracy, although of course that depends on precision engineering that comes at a price. Maybe not, but I am working from the following assumptions: First, since it has been proposed that we just go on straight atomic time, and just use "leap hours" eventually, I take it that it is at least believed by some that: ISTR that according to international agreements UTC must remain within one second of GMT. This is important for navigational purposes - not everyone uses GPS and in any case many wouldn't wish to depend on it as their sole system (remember GPS can be turned off for civilian purposes at any time). From memory even a one second difference between UTC and GMT equates to a quarter mile on the ground. At 30 minute difference would make traditional navigation impossible. -- Andrew Smallshaw |
#13
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Avoiding the Leap Second
On 30 May 2007 17:51:43 -0700, Quadibloc wrote:
Since I'm proposing changing the length of a second, though, by an approximation, rather than the *exact* proportion that adding an extra second would make, this would not lead to TAI minus civil time being an integer number of seconds at least at the start of each new year. There are two possible cures: use the exact proportion instead (adjusted in leap years!), or switch from a longer second to a regular one before the end of the year (for example, splitting the leap second up among all the seconds of the first 360 days of the year would lead to an "even" lengthening of the second in some senses). Do I understand correctly: you are effectively suggesting a redefinition of the civil second from an interval to a count? That is, instead of a civil second being a certain number of atomic vibrations, it's simply determined by having a fixed, integral number of them in some longer time, like a year? That doesn't seem like a bad idea- leap seconds are rather ugly things for ordinary applications to have to deal with. Seems like we should really just have a formal second, and a formal time that is a count of these seconds from some origin. That's the second used for scientific purposes, and the time used for critical applications (power grid sync, phone service, etc). Civil time could be trivially converted to official time (and vise versa). _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#14
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Avoiding the Leap Second
On May 31, 8:49 am, Chris L Peterson wrote:
That doesn't seem like a bad idea Except that it's basically what broadcast radio signals were doing during all of the 1960s up to the end of 1971 (which was called both UTC and GMT, but was really trying to track UT2). It was unworkable for a number of different reasons. For broadcast time signals it only makes sense to transmit based on the most stable time and frequency interval available to your civilization. The current scheme for UTC makes a lot more sense for broadcast signals. In order to have a civil second approximating the mean solar second it would be necessary to modify the infrastructure for distributing civil time such that it was able to handle both kinds of time. This is a major restructuring of the systems that we use on a daily basis. In the economic, practical, engineering sense it is much simpler to abandon leap seconds (and mean solar time) and implicitly say that any problems caused by this can be handled by folks 20 generations from now. (Of course, they said the same thing about pollution, but my bias is showing.) leap seconds are rather ugly things for ordinary applications to have to deal with. No. Leap seconds are a form of resetting a clock. They are an acknowlegement of a horological reality which was understood very well by the navigators of the British Navy 200 years ago, but which we somehow seem to have forgotten in the interim. The reality of running a clock is that no two clocks can ever agree, not even if they are co-located in the same reference frame, in the same laboratory (and there is no agreement between clocks in different reference frames). If one clock is deemed more authoritative then the other has to admit a mechanism by which it can change its offset, its rate, or both. To deny that is to live in a fantasy world and risk the consequences of believing in a system that does not correspond to reality. So the issue is a question of who pays how much, and when, with what sorts of short-term and long-term inconveniences. |
#15
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Avoiding the Leap Second
In article .com,
Quadibloc wrote: Paul Schlyter wrote: Changing the length of the second is out of the question!!! Why? Because a change in the length of the second would affect so many other units which all depend on the second. I'm not proposing that we change the length of a second for purposes of measuring speed and acceleration, so as to change the value of the newton relative to the meter, or to change the volt, the ohm, the joule, or so on. I am merely proposing that we change the second of *civil time* so that it is longer than the 1900 second of Ephemeris Time, also the SI second. That is simply *going back* to the situation we had before atomic time, with leap seconds, was adopted in 1972. Before 1972, UTC time was adjusted in steps of fractions of a second, much more frequently than the frequency of leap seconds. It was to get rid of that mess that leap seconds were introduced. The difference is simply that to compromise with our world in which things are measured with greater precision, I propose that instead of having a second that gradually increases in length in a somewhat messy and indeterminate way, let us have a time scale that is still tied closely to TAI, but by changing the length of the civil second in a controlled manner, so as to produce an effect essentially equivalent to having leap seconds. Since I am proposing lengthening the second *only in those years with leap seconds*, obviously I would not seriously propose that the ohm, volt, et cetera be different in those years too. That would be insanity, and rest assured I suggest no such thing. And how would you determine which years are "those years with a leap second"? Yep, that process too is as unpredictable as the leap seconds. So there would be a need to transform the information about how long a second will last this year ..... it would be just as awkward as the leap seconds themselves. I think applications which really need a time accuracy better than a few seconds over long time interval should use TT, TAI, GPS time, or some other suitable *uniform* time scale *without* *leap* *seconds*! All other applications, where it doesn't matter whether the time is off by a few seconds, should adjust for leap seconds whenever they occur, but ignore leap seconds when computing the time interval between two instants - much like the UNIX time() family of funtions do today. John Savard -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
#16
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Avoiding the Leap Second
In article ,
Chris L Peterson wrote: On 30 May 2007 17:51:43 -0700, Quadibloc wrote: Since I'm proposing changing the length of a second, though, by an approximation, rather than the *exact* proportion that adding an extra second would make, this would not lead to TAI minus civil time being an integer number of seconds at least at the start of each new year. There are two possible cures: use the exact proportion instead (adjusted in leap years!), or switch from a longer second to a regular one before the end of the year (for example, splitting the leap second up among all the seconds of the first 360 days of the year would lead to an "even" lengthening of the second in some senses). Do I understand correctly: you are effectively suggesting a redefinition of the civil second from an interval to a count? That is, instead of a civil second being a certain number of atomic vibrations, it's simply determined by having a fixed, integral number of them in some longer time, like a year? That doesn't seem like a bad idea- leap seconds are rather ugly things for ordinary applications to have to deal with. Seems like we should really just have a formal second, and a formal time that is a count of these seconds from some origin. That's the second used for scientific purposes, and the time used for critical applications (power grid sync, phone service, etc). Civil time could be trivially converted to official time (and vise versa). Having the civil second change length slightly every year would probably be more awkward than the current practice of leap seconds. Chris L Peterson Cloudbait Observatory http://www.cloudbait.com -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
#17
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Avoiding the Leap Second
In article .com,
Quadibloc wrote: Paul Schlyter wrote: But hey! You wanted to go decimal, right? Why should one quadrant be 90 degrees? Why not, say, 100 degrees instead? There is actually such a measure for angles - it's called gons, or (sometimes) "new degrees": one quadrant is 100 degrees and one revolution is 400 degrees. Sometimes this has been used for surveying, and there it fits neatly: while one degree of latitude on the Earth's surface is some 111 km, one "new degree" is very close to 100 km and one "new minute" (equal to 1/100 "new degree" of course) is very close to 1 km. . So the decimal angular units are already there - you just have to start using them! :-) . I thought they were called "grads". They are -- that's another name for them. But, in any case, since you are apparently a stickler for SI units, you should of course know that the official unit for angular measure, the one that fits with everything else in the metric system, is the *radian*. If astronomy would go completely metric, it would have to abandon units like the AU, the solar mass, the parsec, ..... g Of course, it is a little awkward that the number of radians in a right angle, or indeed any aliquot part of the circle, is an irrational, even transcendental, number. One could include pi explicitly in descriptions of angles to get out of this; then, an angle would be called "N pi radians". Since the circle contains 2 pi radians, a protractor with 100 big marks on it to cover 180 degrees, instead of 200 marks, would make sense, covering the expanse from 0 to 1 pi radians. John Savard -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
#18
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Avoiding the Leap Second
Quadibloc (John Savard) wrote: Except for TV stations, that use cesium and rubidium clocks to maintain their frequency on track (and they wouldn't need to do anything, because frequency would still be measured in terms of the SI second, not the second of civil time) nobody else in the private sector uses anything better than a quartz crystal timer. These are accurate to about five seconds a year, so changing the length of a second with an impact of *one* second a year isn't going to impact the real-time clocks in computers or in Internet routers. Instead, only the national time standards people will need to modify their equipment, so they can generate time signals based on longer seconds during those years that require them. So the routers on the Internet would just adjust themselves to WWV from time to time, to avoid being out of sync, presumably as they do now, but because of the changed second (in years requiring leap seconds) this adjustment also automatically takes care of what an explicit recognition of the leap second would have had to do. Many networks have far better accuracy than a quartz crystal timer does. This is from one of the many available network time server boxes, specifying holdover accuracy during GPS outages: == start of quote == | | "NetClock NTP servers are designed to maintain accuracy in the | event of loss of the GPS signal due to severe weather (lightning | strikes, high winds, etc.), physical damage to the antenna, GPS | signal jamming and electromagnetic pulse (EMP), and even if the | federal government disables the GPS signal. Internal oscillators | ensure seamless operation if the GPS signal is lost by maintaining | synchronization accuracy until the GPS signal is restored. | | "A choice of 3 oscillators are available depending on the needs | of the application. A temperature controlled crystal oscillator | (TCXO) is standard. Optional oven-controlled crystal oscillators | (OCXO) and Rubidium-stabilized (Rb) oscillators offer extended | 'holdover' accuracy. | | Oscillator Drift Rate Holdover Accuracy Recommended | (nanosec/sec) (millsec/day) Holdover | | TCXO 2,000 172.8 days | OCXO 20 1.728 months | Rb 0.05 0.1296 years | == end of quote == In many network applications, having two computers be off by up to a second (as in one using SI time and the other using Civil time can be a Very Bad Thing. Consider a computer that falsely concludes that another computer has a newer version of some data and thus overwrites new data with old data. Or a computer that falsely concludes that another computer has an older version of the data and thus refuses to update it's copy. Guy Macon http://www.guymacon.com/ |
#19
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Avoiding the Leap Second
On May 31, 8:38 am, Andrew Smallshaw wrote:
ISTR that according to international agreements UTC must remain within one second of GMT. UTC is under the control of the ITU-R. There is no reason to believe that the ITU-R currently believes this, and lots of reason to believe that they do not. In part this is due to the fact that there really is no such thing as GMT anymore, at least not as any kind of precision entity. The IAU 2000 reforms for earth rotation pretty much abolished the concept. The reformulations which allow re-creation of the previous entities for earth rotation are now given the name "classical" in order to distinguish them from the currently official conventions. From memory even a one second difference between UTC and GMT equates to a quarter mile on the ground. At 30 minute difference would make traditional navigation impossible. If "traditional navigation" means using some sort of almanac, then this is not the case. It is straightforward to predict earth rotation to within one second with a five year lookahead, and the pre- publication lead time even for printed almanacs is less than this. Therefore, with or without leap seconds, the almanacs used for "traditional navigation" can easily change their tabulations such that the users of such traditional methods won't notice the change. |
#20
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Avoiding the Leap Second
Andrew Smallshaw wrote: Secondly, quartz isn't nearly as accurate as you suggest. A 32.768kHz crystal typically has a quoted accuracy of 10ppm. According to my HP-21 that works out at 315 s a year. That's over five _minutes_. That's over a wider temperature than a watch sees. A typical low-cost Casio watch spec is +/- 15 seconds per month, and they often do better than +/- 5 seconds per month in use. |
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