Re: large alignment error with polemaster & mach2

Robert Chozick <rchozick@...>

What degree of polar alignment do most find workable?  I find that Polemaster gets me from 30 arc seconds to one arc minute polar alignment.  Shouldn’t 1 arc minute be sufficient for guiding in most cases?


On Aug 1, 2020, at 5:53 PM, uncarollo2 <chris1011@...> via <chris1011@...> wrote:

Here is some more information:

Note, this covers only the RA drift rate. Dec drift will also always be there no matter how you polar align.


-----Original Message-----
To: <>
Sent: Sat, Aug 1, 2020 5:51 pm
Subject: Re: [ap-gto] large alignment error with polemaster & mach2

The RA tracking rate can vary anywhere from 35 to 70 arc seconds per hour (0.6 to 1.5 arc sec per minute) between the zenith and +- 3 hours from the zenith. The rate of drift is not linear. Modeling creates a drift curve for each point in the sky over the modeled track. The link below can tell you the actual tracking rate for different points in the sky:

These are approximate and depend on perfect polar alignment and not scope flex. In reality the drift can be worse if everything is not perfect. The calculations cover only the atmospheric refraction at nominal temperature and pressure.


-----Original Message-----
From: Andrea Lucchetti <andlucchett@...>
Sent: Sat, Aug 1, 2020 5:35 pm
Subject: Re: [ap-gto] large alignment error with polemaster & mach2

Hi Roland,
I always thought the refraction effect depends on latitude, but can be taken into account using the refracted pole.
do you think the effect is so  big at my latitude?
I leave and image at 42 deg north.

Or do you mean refraction due to altitude over the horizon?

In both cases, I don't understand why I need a model, unless you mean a model with different atmospheric parameters (i.e pressure and temp).
If these are not adjusted night after night , the refraction effect should be  a "factor" not requiring modeling.
It should be just calculated.
Am I missing something?
Thank you again,

Robert Chozick

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