[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 These days Sidereal Time is only used to display to humans in a recognizable format an old and outdated approximation to the current ITRF 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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