[time-nuts] Sidereal time
Neville Michie
namichie at gmail.com
Sat Jun 16 09:57:00 UTC 2012
It started with trying to run two long case regulators on one brick wall.
Although the wall is founded on bedrock they interfere with each other.
As I want to study their performance I tuned one to sidereal time, now they are independent.
I run a TBOLT and a LPRO to maintain a mean time clock for the clock analysis.
I am hoping to get a chip from TVB to divide the TBOLT or rubidium 10MHz down to PPS at sidereal rate to observe the
performance of the sidereal regulator. Now I want to be able to set the sidereal time standard so, if I lose power on my
rubidium, I can reset it so the longterm record of the sidereal long case will have no phase jumps.
Also it seemed like a good idea, and the more it seems difficult, the more it needs to be done.
cheers,
Neville Michie
On 16/06/2012, at 5:51 PM, Ken Duffill wrote:
> Hi,
>
> First of all why would you want Sidereal Time to that level of precision?
>
> I know this is the time-nuts so 'because I can' is a perfectly acceptable answer.
>
> These days Sidereal Time is only used to display to humans in a recognizable format an old and outdated approximation to the current ITRF <-> ICRF transformations that the professionals would use to find or track a celestial object.
>
> See IERS (http://www.iers.org/IERS/EN/DataProducts/data.html) and SOFA (http://www.iausofa.org/index.html) for the details and sample code in FORTRAN and 'C' for these transformations.
>
> I suspect if you want microsecond accuracy you will have to use the SOFA routines, and have access to the IERS EOP Data.
>
> Cheers
>
> Ken
>
> On 16/06/12 07:20, Chris Albertson wrote:
>> On Fri, Jun 15, 2012 at 9:49 PM, Mark Sims<holrum at hotmail.com> wrote:
>>
>>> Lady Heather can do sidereal time. Specify either the LMST, LAST, GMST
>>> or GAST time zone (for Local/Greenwich Mean/Apparent Sidereal Time).
>>
>> I think the question was how to get Sidereal time to the microsecond level.
>> A computer display screen only gets refreshed roughly 60 to 100 times per
>> second so a screen can be tens of milliseconds off.
>>
>> How is this done professionally. Basically they don't. What you do is
>> record a UTC time code on a track parallel to the data. Or now that
>> everything is digital, the time code is sampled and multiplexed with the
>> data. Later the display software can convert the time to whatever format
>> is desired.
>>
>>
>
>
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