Re: [LEAPSECS] Consensus building 2
Stephen Colebourne said: Local time * definition: local-time - the time-scale local to a region of the Earth * definition: offset - the duration that local-time differs from the locally recognised legal standard time-scale Sorry, that's nonsense. By definition, that offset is always zero, since local-time is always equal to the locally recognized legal standard time-scale. What you mean is the difference between local-time and some global timescale such as UT1, UTC, or TAI. * definition: time-zone - a region of the Earth where local-time is coordinated coordinated with what? Local time in the whole EU (minus those bits in the Americas) is coordinated, but it's not all the same. Try a region of the earth where local time is intended to be the same throughout that region at any time of the year. Note that there are a slew of issues that this still glosses over. For example, the UK and Portugal are currently both in UTx+0100 between certain dates and UTx+ the rest of the year, but in the past they had different changeover dates. Does this make them one time zone or two? [Olsen finesses this; an Olsen timezone is a region of a single country, and the always the same rule only applies from 1970 onwards.] As another example, if one country bases its legal time on UT1 and another on UTC, can they be in the same time zone? * the offset from local-time to TAI-2008 can be calculated given what? And why is this not true for UTC-1972-offset? Or UT1-offset? Humanity - definition: humanity-day - a non-scientific, commonly used term understood by 6bn humans I don't accept that that is a commonly used term. Rather, it's a term you've invented for these discussions, defined by: * a humanity-day is interpreted in line with the rising and setting of the Sun at a single Earth location (and I don't have a problem with that, so long as you're honest about it). -- Clive D.W. Feather | If you lie to the compiler, Email: cl...@davros.org | it will get its revenge. Web: http://www.davros.org | - Henry Spencer Mobile: +44 7973 377646 ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Consensus building 2
On Wed, 2 Feb 2011, Gerard Ashton wrote: The point below should be * definition: UTC-1972-day - a duration of 86399, 86400, or 86401 seconds. On 2/2/2011 8:50 PM, Stephen Colebourne wrote: * definition: UTC-1972-day - a duration either 86400 SI-seconds or 86401 SI-seconds long To be precise they are TAI seconds. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ HUMBER THAMES DOVER WIGHT PORTLAND: NORTH BACKING WEST OR NORTHWEST, 5 TO 7, DECREASING 4 OR 5, OCCASIONALLY 6 LATER IN HUMBER AND THAMES. MODERATE OR ROUGH. RAIN THEN FAIR. GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Consensus building 2
Update including some comments sent earlier, and new entries on UTC and local-time: A star is used for a new or amended line. General: - these points of consensus exist to aid the understanding of leap seconds not time in general - the terms seconds, minutes, hours and days are overloaded - relativistic effects do not significantly impact the understanding of leap seconds - definition: a time-line is the general passage of time - definition: instant - an instantaneous point on the time-line - definition: duration - the length of a portion of the time-line - definition: time-scale - a set of rules giving meaning to an instant - the length of time between two instants is a duration * definition; ISO-8601 - a standard format for expressing date-times (defined in detail elsewhere) SI - definition: SI-second - a standardised unit of measurement for durations (defined in detail elsewhere) - the accurate measurement of an SI second is complex and typically achieved via cooperation - the SI-second forms the basis for many other fundamental units of measure - the duration of an SI-second is considered to be constant TAI - definition: TAI-2008 - a time-scale commonly named TAI last revised in 2008 (defined in detail elsewhere) - the accurate measurement of TAI is complex and typically achieved via cooperation - the TAI-2008 time-scale is defined as a uniformly increasing count of TAI-seconds from a fixed epoch - definition: TAI-2008-second - the same as SI-second for the purposes of this discussion * TAI-2008 is usually denoted using ISO-8601 with a day implied as exactly 86400 TAI-seconds Solar - definition: solar-time - time measured by the rotation of the earth relative to the Sun - apparent-solar-time and mean-solar-time are two forms of solar-time - the accurate measurement of solar-time is complex and typically achieved via cooperation - definition: mean-solar-day - the descriptive subdivision used when describing mean-solar-time - the length of a mean-solar-day in SI-seconds varies over time and is not a fixed number of SI-seconds - the length of a mean-solar-day in SI-seconds is on average increasing with time UT * definition: UT - a time scale based on the rotation of the Greenwich meridian relative to the Sun (defined in detail elsewhere) - UT has a number of variants, the most common are UT1 and UTC - the accurate measurement of variants of UT is complex and typically achieved via cooperation - definition: UT1 - a smoothed variant of UT (defined in detail elsewhere) - definition: UT1-day - the subdivision used when expressing UT1 - the length of a UT1-day in in SI-seconds varies over time and is not a fixed number of SI-seconds - the length of a UT1-day in in SI-seconds is on average increasing with time - definition: UT1-second - a fraction 1/86400 of a UT1-day - the duration of a UT1-second is close to, but not equal to an SI-second - UT1 is the most commonly recognised form of mean-solar-time - a UT1-day is the most commonly recognised form of mean-solar-day UTC-1972 - definition: UTC-1972 - a time-scale commonly named UTC last revised in 1972 (defined in detail elsewhere) - the accurate measurement of UTC is complex and typically achieved via cooperation - the UTC-1972 time-scale is a continuous count of SI-seconds - the UTC-1972 time-scale defines UTC-1972-days * definition: UTC-1972-day - a duration that is normally 86400 TAI-seconds but can be 86399 or 86401 SI-seconds * the missing or additional TAI-second in a UTC-1972-day is a negative or positive leap-second * a leap-second is removed or inserted at the end of a UTC-1972-day * an inserted leap-second has a representation of 23:59:60 - the presence or absence of a leap-second is currently determined up to 6 months in advance * leap-seconds are used with the aim of keeping UT1 and UTC no more than 0.9 SI-seconds apart - leap-seconds are currently added about once every 18 to 24 months - UTC-1972 is an integral number of SI-seconds different from TAI-2008 * UTC-1972 is usually denoted using ISO-8601 without inclusion of the difference to TAI-2008 Local time * definition: local-time - the time-scale local to a region of the Earth * definition: offset - the duration that local-time differs from the locally recognised legal standard time-scale * definition: time-zone - a region of the Earth where local-time is coordinated * definition: time-zone-rules - rules defining how the offset changes along the time-line * definition: UTC-1972-offset - the duration that local-time differs from UTC-1972 * the offset from local-time to TAI-2008 can be calculated * definition: TAI-2008-offset - the duration that local-time differs from TAI-2008 * given either a TAI-2008-offset or a UTC-1972-offset and a leap-second table the other may be calculated Humanity - definition: humanity-day - a non-scientific, commonly used term understood by 6bn humans * a humanity-day is interpreted in line with the rising and setting of the Sun at a single Earth location -
Re: [LEAPSECS] Consensus building 2
On 2011-02-04 00:32, Stephen Colebourne proposed the following description: - definition: TAI-2008-second - the same as SI-second for the purposes of this discussion The TAI time scale uses the SI second alright, but it is the value of the SI second as realized on the rotating geoid. You get a different time scale if you use the SI second at other points in spacetime, such as the geocenter. And if you extend TAI from the geoid to other places close to the surface of the Earth, using a coordinate system corotating with the Earth, you will find that the TAI second differs from the SI second as realized at these places. I fully agree with you that this is irrelevant for leap seconds -- but for the definition of TAI it is relevant. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Consensus building 2
The point below should be * definition: UTC-1972-day - a duration of 86399, 86400, or 86401 seconds. On 2/2/2011 8:50 PM, Stephen Colebourne wrote: * definition: UTC-1972-day - a duration either 86400 SI-seconds or 86401 SI-seconds long ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Consensus building 2
* definition: UTC-1972-day - a duration either 86400 SI-seconds or 86401 SI-seconds long or 85999 * leap-seconds are added to UTC-1972 with the aim of keeping UT1 and UTC no more than 0.9 SI-seconds apart Leap seconds may be inserted or deleted, though so far there have only been insertions, and the way things are going there are unlikely to ever be any deletions. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Consensus building 2
On 02/02/2011 18:50, Stephen Colebourne wrote: OK, so we've got a little bogged down in redefining what appear to be well defined things, and whether a list like this should define things anyway. I'll give it one more go, but sadly I don't have the patience of Job if others don't also want consensus. Remember, I'm not an expert to the same degree as others on this list. Thus statements I make will be simplistic, but are the question is whether they are good enough for the problem at hand? Writing a clarification is only helpful if you propose a better statement to replace that you are objecting to. Thanks for the update. It is a lot closer... A star is used for a new or amended line. General: * these points of consensus exist to aid the understanding of leap seconds not time in general * the terms seconds, minutes, hours and days are overloaded * relativistic effects do not significantly impact the understanding of leap seconds * definition: a time-line is the general passage of time * definition: instant - an instantaneous point on the time-line * definition: duration - the length of a portion of the time-line * definition: time-scale - a set of rules giving meaning to an instant * the length of time between two instants is a duration SI * definition: SI-second - a standardised unit of measurement for durations (defined in detail elsewhere) * the accurate measurement of an SI second is complex and typically achieved via cooperation - the SI-second forms the basis for many other fundamental units of measure TAI * definition: TAI-2008 - a time-scale commonly named TAI last revised in 2008 (defined in detail elsewhere) * the accurate measurement of TAI is complex and typically achieved via cooperation Accurate creation of TAI is compled and achieved via cooperative measurements. TAI isn't measured directly, but created after the fact based on the measurements input. A subtle point, but one worth remembering. * the TAI-2008 time-scale is defined as a uniformly increasing count of TAI-seconds from a fixed epoch * definition: TAI-2008-second - the same as SI-second for the purposes of this discussion * TAI-2008 does not definitively imply a definition for minutes, hours and days Solar * definition: solar-time - time kept or measured by the Sun * apparent-solar-time and mean-solar-time are two forms of solar-time * the accurate measurement of solar-time is complex and typically achieved via cooperation * definition: mean-solar-day - the descriptive subdivision used when describing mean-solar-time * the length of a mean-solar-day in in SI-seconds varies over time * the length of a mean-solar-day in in SI-seconds is on average increasing with time * the length of a mean-solar-day is not a fixed number of SI-seconds UT * definition: UT - a time scale based on the rotation of the Earth (defined in detail elsewhere) * UT has a number of variants, the most common are UT1 and UTC * the accurate measurement of variants of UT is complex and typically achieved via cooperation * definition: UT1 - a smoothed variant of UT (defined in detail elsewhere) * definition: UT1-day - the subdivision used when expressing UT1 * the length of a UT1-day in in SI-seconds varies over time * the length of a UT1-day in in SI-seconds is on average increasing with time * the length of a UT1-day is not a fixed number of SI-seconds * definition: UT1-second - a fraction 1/86400 of a UT1-day UTC-1972 * definition: UTC-1972 - a time-scale commonly named UTC last revised in 1972 (defined in detail elsewhere) * the accurate measurement of UTC is complex and typically achieved via cooperation * the UTC-1972 time-scale is a continuous count of SI-seconds * the UTC-1972 time-scale defines UTC-1972-days * definition: UTC-1972-day - a duration either 86400 SI-seconds or 86401 SI-seconds long - the additional SI-second in a UTC-1972-day is a leap-second * the presence or absence of a leap-second is currently determined up to 6 months in advance * leap-seconds are added to UTC-1972 with the aim of keeping UT1 and UTC no more than 0.9 SI-seconds apart * leap-seconds are currently added about once every 18 to 24 months * UTC-1972 is an integral number of SI-seconds different from TAI-2008 Humanity * definition: humanity-day - a non-scientific, commonly used term understood by 6bn humans - a humanity-day is interpreted in line with the rising and setting of the Sun * the legal definition of a day varies by country * the legal definition of a day may be based on UTC-day, mean-solar-day or humanity-day Maybe more controversial * UT1 is the most commonly recognised form of mean-solar-time * a UT1-day is the most commonly recognised form of mean-solar-day Agreed up through here. * a UT1-day is the most commonly recognised form of a humanity-day Not sure I'd agree on this point... We've had 40-odd years where the humanity day has been a UTC day not a UT1 day. But the delta between these is small. A humanity-day works well with
