[time-nuts] Sidereal time

Ken Duffill k.duffill at ntlworld.com
Sat Jun 16 07:51:10 UTC 2012


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recognizable format an old and outdated approximation to the current 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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