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Re: [TowerTalk] And now for something completelydifferent(TrueNorth)

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Subject: Re: [TowerTalk] And now for something completelydifferent(TrueNorth)
From: "K8RI on TowerTalk" <>
Date: Sun, 17 Sep 2006 16:38:01 -0400
List-post: <>
>From: "Jim Lux" <>

> Actually, though, the other link I posted (about using polaris) is 
> fascinating.. It makes the point that with a standard theodolite 
> telescope, Polaris is visible in the daytime, and because it moves a lot 
> slower (angular wise) than the sun, it's easier to get a good north 
> direction.  I'll have to give it a try.
The spotting scope on my larger telescope 2500mm @ f10 (don't remember the 
spotting scope magnification, but the objective is 50mm for light gathering) 
has not only cross hairs, but a graduated rail road track so when things are 
properly aligned polaris will travel around that track.  Polaris is not all 
that bright and can be difficult to spot (naked eye) in heavily light 
poluted skys yet you can see it in the daytime in a scope. Even with a 
relatively low power eyepiece I have to crank the main scope off to one side 
or the other to find Polaris.  If not properly set up even being off a 
little will cause stars to drift noticeably in a shot time. OTOH the beam 
width of that 2500 f-10 is a some what narrower than that of my 

What we've really been doing is trying to apply telescope alignment to 
antenna alignment where the telescope has a "beam width"/viewing angle 
measured in minutes instead of degrees while the antenna beamwidth is 
probably hundreds or even thouands of times wider.

When running a camera with a 28 to maybe 100 mm lens piggyback on the scope 
I still resort to "that looks about right" for the alignment and it works 
for up to about 5 minute exposures. Around 100 mmm I have to turn the drive 
motor on and can easily do 10 minutes unguided.

These are two different realms with far different requirments. Applying the 
far greater astronomical precision requirements to antenna alignment hurts 
nothing, but gains nothing as well. OTOH is good experience<:-))

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2 (Use return address from home page)

>>Roger Halstead (K8RI and ARRL 40 year Life Member)
>>N833R - World's oldest Debonair CD-2
>> >
>> > No. The north star makes a little circle about 1.5 degrees in
>> > diameter around the true north point. (RA 02 31 49.08, Decl +89 15
>> > 50.8 in J2000 coordinates) so it's about 3/4 degree off celestial north
>> > pole.
>> >


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