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ideal star to choose for All Star Polar Alignment?

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#1 end

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Posted 13 March 2013 - 04:18 PM

Hi all,

Through some recent reading and thinking further on this subject it occurred to me (yes, I'm not quick!) that not all stars are created equal when it comes to selecting a good star for Celestron's All Star Polar Alignment. I've been using Celestron mounts for about 18 months and have had good results with the ASPA, but sometimes the star I choose results in more difficult adjustment. While it is true that you can select any star you want for this process, some of them will be easier to use than others as changes in the alt / az screws will have more or less effect on the perceived position of a star.

So here is the question: Ignoring star brightness, is it true that the best* star to select would be at or near the intersection of the meridian and the equator?

* For this question best is defined as resulting in the the most accurate result and easiest adjustment.

#2 rockethead26

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Posted 13 March 2013 - 04:51 PM

I use this free program called Best Pair II. It seems to take all the guess work out of the equation. Works for me.

#3 end

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Posted 13 March 2013 - 05:34 PM

Thanks for the link, but this is for selecting good stars for your goto alignment and not for polar alignment. What I'm looking for is the best star to select for the ASPA procedure.

#4 Peter in Reno

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Posted 13 March 2013 - 05:45 PM

I used to have CPC0800 mounted on a wedge. After GoTo Star Alignments, then I use ASPA. The ASPA star I pick is near the Meridian and fairly high in the sky. I would say about 45 - 60 degrees above horizon, (Zenith is 90 degrees). I think this also apply to Celestron GEM mounts as well. It's on page 37 of CGEM operating manual:

"Once your telescope is aligned on two stars and at least one additional calibration star, slew the telescope to any bright star in its Named Star database list. For best results choose a polar alignment star that is high in the sky and near the Meridian. Try to avoid stars that are close to the west/east horizon, directly overhead or too near the celestial pole. Once there, press the Align button and use the Up/Down buttons on the hand controller to select Polar Align from the list."

Peter

#5 cn register 5

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Posted 13 March 2013 - 06:01 PM

Yes, a star near the meridian and not too high makes a good choice for an ASPA. Not so close that you cross the meridian during the alignment.

I tend to point the scope South and not too high, then do an identify to choose a suitable named star.

Chris

#6 HowardK

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Posted 13 March 2013 - 06:46 PM

I goto the nearest star that sits closest to both the meridian and celestial equator

#7 rockethead26

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Posted 13 March 2013 - 08:29 PM

Thanks for the link, but this is for selecting good stars for your goto alignment and not for polar alignment. What I'm looking for is the best star to select for the ASPA procedure.


Ah, sorry. I saw ASPA, but it didn't register.

#8 WadeH237

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Posted 13 March 2013 - 10:10 PM

I think that the best star would be one due south very near zero degrees declination.

-Wade






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