Ok so you really are NOT needing the EOP Data that deals with the
irregularities of the Earth Rotation.
In fact it sounds to me like you are not really looking for Sidereal
time at all. Sidereal Time is not a uniform time scale and so sounds
like it is inappropriate for your needs.
If you get a source of Sidereal Time, from somewhere that claims to be
able to give it to you to microsecond accuracy, there is a high
probability that they will be taking things like nutation into account.
Certainly if you use the SOFA routines I alluded to earlier they will.
Again it sounds to me like what you are really looking for is an
independent source of uniform time based on the PPS produced by the
divider in the chip TVB will get for you, which is then very close to
the MEAN sidereal second.
The way Astronomers used to do it, they would have clocks regulated to
the mean Sidereal Second, but have to recalibrate them every day
(actually every night!). And they were not interested to the
microsecond. It was the search for that level of accuracy that forced
them to move away from this non-uniform timescale and produced the
ICRF/ICRS and ITRF/ITRS that they now use.
HTH
Ken
On 16/06/12 10:57, Neville Michie wrote:
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an old and outdated approximation to the current ITRF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<hol...@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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