[LEAPSECS] the big artillery

[Richard Clark]

Well, for historical and archival purposes Julian date nearly always means
traditional days, as in solar days. But for astronomical uses a fixed
unit, the apocryphal atomic day is implied. This means needing to know
delta T if you need to relate it back to a civil date or time.

The term 'day' has an awful lot of linguistic baggage that clearly
implies that the solar day is meant. But now the use of 'day' can be
at the speaker's and listener's risk.

The minute, hour, day, year... these are not SI units. We need to
start considering it sloppy to use them as if they are.

Do we mean 'atomic day'? If so we need to:
  1. say so, and
  2. make it official by defining, rather than just implying one.

Perhaps hectosecond would be better. At least it doesn't invite
confusion.

Yeah, and now to convince anyone to do this.

Richard Clark


On Thu, 30 Oct 2014, Dennis Ferguson wrote:

> I see Terrestrial Time being expressed as a Julian Date quite
> a lot.  What is the unit of that number if not "Day"?
>
> Dennis Ferguson
>
> On 30 Oct, 2014, at 09:16 , Rob Seaman <seaman at noao.edu> wrote:
>> "Day" is a fundamental physical fact about a planet or moon.  "Minute" is an artificial concept.  Its intuitive role as a fraction of a day takes precedence over serving as a round number of equally artificial SI seconds.  There are two kinds of time that must be accommodated.
>>
>> Rob Seaman
>> NOAO
>> --
>>
>>> On Oct 30, 2014, at 8:06 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
>>>
>>> In message <20141030143121.GA20281 at ucolick.org>, Steve Allen writes:
>>>
>>>> I wonder if the ITU-R process can go to its completion without
>>>> introducing any document which points out that to omit leap seconds
>>>> from a time scale called UTC is to redefine the word "day".
>>>
>>> You mean the same way leapseconds redefine "minute" by making
>>> them have the counter intuitive numbers of seconds ?
>>
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