[time-nuts] BYMLBI (Back Yard Medium LBI)

[Brooke Clarke]

Hi Bruce:

Thanks for the link.  I learned after I moved here that our town of 
Ukiah, Calif. was one of a handful of locations to have a Latitude 
observatory.
http://www.prc68.com/I/UkiahObs.shtml
The Zenith Telescope that's over 100 years old has angular accuracy 
that's maybe 100 times better than the Paramount ME mount.
It's interesting that the Photographic Zenith Tube (PZT) was compared to 
the Zenith Telescope and the results were essentially the same.  NBS 
used the PZT to set it's pendulum clocks for some time.
I have a feeling that the 7 inch transit circle is a very expensive 
instrument and that there's no low cost commercial equivalent.

Have Fun,

Brooke Clarke
http://www.PRC68.com


Bruce Griffiths wrote:
> The Naval Observatory and others have been doing this for years albeit 
> averaged over several observations and by fitting curves to the 
> stellar transit path in the transit circle focal plane eg:
>
> http://adsabs.harvard.edu/full/1986IAUS..109..483H
>
> The setup with Heidenhain elevation encoders etc was impressive when I 
> visited the facility in the 1980's.
> The accomodation etc was in stark contrast to the Observatory a little 
> further up the hill where we only had underfloor heating and didnt 
> obseve from the comfort of a temperature controlled computer room.
>
> Bruce
>
> Brooke Clarke wrote:
>> Hi Bruce:
>>
>> From what I can learn about "seeing" the atmosphere instability is 
>> too great to allow making measurements optically in the 1 ms area.
>>
>> It's a couple of acres.
>>
>> Have Fun,
>>
>> Brooke Clarke
>> http://www.PRC68.com
>>
>>
>> Bruce Griffiths wrote:
>>> Brooke Clarke wrote:
>>>> Hi:
>>>>
>>>> For a number of decades I've tried to figure out a way to measure 
>>>> the period of the Earth's rotation accurate to at least 1 ms.
>>>> For some thoughts (since I don't think it will work) on doing it 
>>>> optically see:
>>>> http://www.prc68.com/I/StellarTime.shtml
>>>>
>>>> Is it possible to do it using a radio method in my (large) back yard?
>>>>
>>>
>>> 1ms corresponds to an angle of 15 milliarcsec or 73 nrad for 0 
>>> declination objects.
>>>
>>> 15 milliarc sec positioning accuracy is just within the capability 
>>> of an 7" aperture transit circle or PZT equipped with a CCD camera.
>>> This accuracy was close to that achievable with a video camera 
>>> equipped transit circle in the late 1980's.
>>>
>>> A 2900 km diameter dish or equivalent has a resolution of about 73 
>>> nrad at 1420MHz.
>>> Position accuracy for a point source can be somewhat higher than the 
>>> resolution if the SNR is sufficiently high.
>>> However an antenna system of several hundred km in extent is likely 
>>> to be necessary.
>>>
>>> Just how large is your backyard?
>>>
>>> Bruce
>>>
>>>
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