Sidereal Time is another form of Earth Orientation angle based time
where the orientation angle reference is the "fixed stars" instead of
the mean sun.
You need to take such effects as precession, nutation and polar motion
into account.
The rate isn't uniform with respect to atomic time.
The (rate) ratio of UT1 to mean sidereal time is defined to be
0.997269566329084 − 5.8684×10−11T + 5.9×10−15T², where T is the number
of Julian centuries of 36525 days each that have elapsed since JD
2451545.0 (J2000).
If you are using UTC broadcasts to determine Sidereal time, you first
need to correct UTC to obtain UT1 by applying the correction DUT1 ( UTC
-UT1).
DUT1 predictions etc are available from IERS.
Bruce
Neville Michie wrote:
It is an interesting question, we are so used to WWV and GPS with
regular time signals to synchronise clocks to mean solar time.
One method is to get a pocket calculator to identify a time in the
future when a siderial second nearly corresponds to a UTC second
and use the PPS pulse from GPS to jam a preset time into the Siderial
clock, (or start a halted clock with the correct time preset.
How long you have to wait for corresponding seconds depends on how
accurate you want it.
cheers, Neville Michie
On 15/01/2010, at 2:25 PM, Bruce Griffiths wrote:
Brian Kirby wrote:
I would like to have an electronic clock to keep sidereal time. I am
planning on using a HP 59309A, which can except an external clock of
1/5/10 Mhz.
According to Wikipedia sidereal time is 23 hours 56 minutes and
4.091 seconds - a total of 86,164.091 seconds
So 86,400 seconds for a normal "atomic defined" day divided by
86,164.091 = 1.002,737,903,89
If I set the 59309A to 10 Mhz external clock and dial a synthesizer
up to 10.0273790, the unit should be able to keep sidereal time.
Is my math and theory correct ?
Brian - KD4FM
That just gives the rate.
How are you going to set the actual Sidereal time to better than the
0.9s that can be deduced from UTC?
Bruce
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