[time-nuts] Sidereal time

J. Forster jfor at quik.com
Fri Jan 15 20:44:02 UTC 2010


These are all OPEN LOOP corrections. They are better than nothing, but
nowhere near as good as properly implemented auto-guiding which is closed
loop.

They are certainly not as good as even the simplest Adaptive Optics
utilizing only a Tip-Tilt tracker.

-John

==================

> 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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>
>
>
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