[time-nuts] Why not TAI?
mike cook
michael.cook at sfr.fr
Thu Aug 11 07:52:36 UTC 2011
Le 11/08/2011 08:57, Attila Kinali a écrit :
> On Wed, 10 Aug 2011 16:35:11 +0200
> cook michael<michael.cook at sfr.fr> wrote:
>
>>> If TAI is a paper clock, what else should be used if a strictly monotone
>>> time scale is needed?
>> Do you have any specific application in mind?
>> If you need an SI seconds rated scale, then you need something based on
>> TAI. GPS time has a TAI second rate and is monotonic. But of course you
>> would need a GPS receiver to access it.
> I don't have a specific application in mind. Just a general question
> on what should be used. But lets say i want to have a monotonic clock
> for a computer system to timestamp events precisely and unambigously.
>
> Yes, using GPS time (with or without going back to TAI) would be
> a probable solution.
>
> Are there any other time scales available that would fit that need?
>
> Attila Kinali
>
Well, there is :
TT, Terrestrial Time, which is uniform (interval SI second), monotonic ;
with an epoc of
00h 00m 00s 1 Jan 1977 TAI with a constant offset such that [TT] = [TAI]
- 32.184s .
Or more exotic:
ET, Ephemeris Time, which is uniform and monotonic with a non SI second
of 1/31566925,9747 of the tropical year of 1900.
Julien Date is another , using SI second, but a numeric day label with
an epoc of initial epoc defined as (UT) at midday on Monday Jan 1 4713
BC in the Julian calendar. It is measured in days and fractions with
precision of about a millisecond and being numeric is so is easy to do
calculations on.
MJD , Modified Julien Date is the above -2400000,5 to keep the numbers
down. This was recognised as a time scale by the IUT. I think it is now
deprecated but is in common use.
There are probably others.
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