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. 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 * 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 * a UT1-day is the most commonly recognised form of a humanity-day * the duration of an SI-second is considered to be constant * the duration of a UT1-second is close to, but not equal to an SI-second Stephen _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs