[time-nuts] Sidereal time

Brooke Clarke brooke at pacific.net
Fri Jan 15 18:17:47 UTC 2010

Hi Brian:

Why?  Do you just want to see the sidereal time on a display or do you 
need a digital output?
The Spark Fun "serial enabled" displays use what's called a "back pack" 
that has the PIC 16F88 uC and it's used to do serial data to LCD 
parallel data can control lines.  I've made some clocks using that chip.

A friend is setting up an observatory where the pointing accuracy of the 
telescope mount is specified as " 7 arcseconds or less peak-to-peak 
periodic error before correction". Much better after correction.  That 
implies he needs to know what time it is within tens of milliseconds.
We looked into different ways to get the time into his computer to that 
accuracy and NTP looks like it will fill the bill, so a GPS receiver may 
not be required.

Have Fun,

Brooke Clarke

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
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