[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recognizable format an old and outdated approximation to the current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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