[LEAPSECS] Consensus building?
scolebourne at joda.org
Wed Feb 2 13:44:42 EST 2011
On 2 February 2011 18:13, Warner Losh <imp at bsdimp.com> wrote:
>> - an SI-based-minute is formed from exactly 60 SI-seconds
>> - an SI-based-hour is formed from exactly 60 SI-based-minutes and thus
>> exactly 3600 SI-seconds
>> - an SI-based-day is formed from exactly 24 SI-based-hours and thus
>> exactly 86400 SI-seconds
> These are true only most of the time. On leap second day, they are all
> false and off by 1, typically one low. It all depends on the timescale that
> you use, and thus there can't be a universal definition here.
You're reading more into the statement than is intended by trying to
interpret them as a time-scale or clock. I'm defining a unit of
SI-based-minute that is a multiple of 60 of the unit SI-second. No
more no less.
>> - a solar-day is a measured period of time
>> - the length of a solar day in in SI-seconds varies over time
>> - the length of a solar day in in SI-seconds is on average increasing with
>> - a solar day is not a fixed number of SI-seconds
>> - a solar-hour is the period of 1/24th of a single measured solar-day
>> - a solar-minute is the period of 1/60th of a solar-hour and thus
>> 1/1440th of a single measured solar-day
>> - a solar-second is the period of 1/60th of a solar-minute and thus
>> 1/86400th of a single measured solar-day
> Except that the last bits are wrong here too. It isn't the measured solar
> day, except for UT, but the average of the measured day smoothed in
> different ways for UT1 and UT2.
> Also, implicit in this definition is the astronomical term solar-day, so
> your definition is circular. A solar day is the amount of time it takes the
> earth to rotate until the sun is in the same apparent position in the sky,
> as opposed to a sidereal day, which is 360 degrees of rotation.
So why not tweak these, or try to build consensus around a different
set of statements?
>> - the UTC-2011 time-scale is known as UTC in the year 2011
>> - the UTC-2011 time-scale is a continuous count of SI-seconds
>> - the UTC-2011 time-scale defines UTC-2011-days
>> - a UTC-2011-day is either 86400 SI-seconds or 86401 SI-seconds long
>> - the additional SI-second in a UTC-2011-day is a leap-second
>> - the presence or absence of a leap-second is determined up to 6
>> months in advance
> yes. This time Bulletin came out this morning, giving only 5 months of
> notice of no leap second.
> I'm also not sure that this notation is the best. We're really using
> UTC-1972 right now, if we follow the convention of using the year of the
> last change. We'd also be on TAI-2008 based on the last time the averaging
> algorithm of TAI was changed.
We should use UTC-1972 as a terminology if has broader agreement.
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