[time-nuts] Sidereal time

[Bruce Griffiths]

One needs to know the local apparent sidereal time to aid initial 
acquisition of the target.
Periodic error correction and using an autoguider are of little or no 
use for this operation.

However correction for encoder error axis non orthogonality, encoder 
eccentricity and bending of the telescope tube an the mount may be required.
A pointing model for the telescope is derived from the pointing (not 
tracking errors) errors for a set of target objects uniformly 
distributed over the sky.
For further details see:

http://www.tpsoft.demon.co.uk/

Bruce

Jim King wrote:
> I'm not sure your friend needs the time at all.  Telescope tracking 
> mounts have a periodic error due to non-perfect mechanical parts.  The 
> usual way to remove this error is to "train" the mount by manually 
> guiding it through one or more periods, or - probably more common 
> these days - use an optical autoguider.
>
> Jim
>
> On 1:59 PM, Brooke Clarke wrote:
>> 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.
>> http://www.prc68.com/I/PIC16F88.shtml
>> http://www.prc68.com/I/PRC68COM.shtml#07092006
>>
>> 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.
>> http://www.prc68.com/I/StellarTime.shtml#StrMov
>> 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
>> http://www.PRC68.com
>
>
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