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The Nexstars are as far as I know, all fork mounted jobs so a polar scope is out of the question.
Ken's method should work ok upto and including point 4.
The nexstar is a gps thing I believe and therefor might behave a bit differently from the Meade classic LX200. Assuming the gps can be turned off and the inbuilt electronic compass if it has one , turned off as well, the idea would be to start out with the forks level horizontally, and the ota set to -90 deg dec. then impliment Ken's method.
If you'd like to try mine, perhaps I should explain in a little more detail the rationale behind it.
With any polar mode 'goto' system, there are a number of assuptions made by the control electronics:
1. the polar axis is pointing exactly at the celestrial poles.
2. the correct siderial time + time zone offset have been entered.
3. the correct date has been entered.
4. the correct latitude and longitude have been entered.
Neglecting arguments about 1,2 or 3 star alignments,or no alignment,
lets just say that one star has been selected and the mount told it is aligned.
From this position the mount can calculate the movements needed to point to any selected object within range.
So now then, if I enter data in accord with points 2,3&4, I have only point 1 missing.
The mount knows no difference if I use a 1 star alignment and accept the position as correct, it will assume it is in fact pointing at the chosen alignment star even if it is in fact pointing in the opposite direction.
So if I now physically move the mount while it is still tracking, adjusting the altitude and the azimuth until the guide star is now in the EP, it follows that the polar axis must necessarily be pointing very close to the SCP, even if I was totally disorientated and began with the mount pointing north. In that case I would have to move the mount thru 180 degrees azimuth to get the star in the EP.
I had to use this method or else a more tedous meridian transit method because I simply can't see the SCP from my location, and there is too much ferous material nearby for a compass to work (from which to measure deviation).
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