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North Celestial Pole

Started by brucesdad13, 01/20/2015 09:18AM
Posted 01/20/2015 09:18AM | Edited 01/20/2015 09:19AM Opening Post
Hi all, I'm starting to get the hang of setting up the C8 and ASGT mount and am not having tremendous accuracy with the Goto. I've finally figured out where Polaris is from my back yard. I'm a slow learner (lol wink ). I did align the optical axis on my polar axis finder scope and so at least that's working out...

Not having any sort of permanent place to setup the tripod I used spray paint to mark where the tripod legs have been that's pretty close to aiming north. I removed the polar alignment scope and looked through the opening with the naked eye and moved the tripod until I could see Polaris. Then I put the polar scope back into the mount and adjusted the various screws until Polaris was in side the circle on the perimeter of the circle surrounding the NCP.

I feel like Cassiopeia has been the easiest to see. In fact I'm not sure I have been able to discern the big dipper. The pattern etched in the polar scope is black and hard to see, if at all, against the sky. I've found that shining my red light into the hole a bit from the top illuminates the pattern while allowing me to see Polaris. Cassiopeia doesn't seem to match the location in the sky in relation to where I've positioned Polaris. I'm not sure if I'm doing something wrong... (see attached image).

Anyways I figured it was closer than I've ever gotten before to being polar aligned. I adjusted the azimuth screws so that it was horizontally in the right place. I then adjusted the altitude screw so that it was vertically in the right place. I followed the manual "make final adjustments in altitude by moving the mount against gravity (i.e. using the rear latitude adjustment screw to raise the mount)" and removed the front latitude screw. Then I tightened the mount to the tripod and confirmed Polaris was still in the small circle.

Once Polaris is in the small circle do I then lower the altitude back to my latitude? It seems like the polar axis was much higher... Thanks for your help!

Attached Image:

brucesdad13's attachment for post 59026

~ Charlie Stevenson

8" f/5.7 String Telescope - 1st Scope Build; 2nd Place Stellafane 2016 Optical Award for Newtonians 12.5" and Smaller
10" f/4.5 Newtonian (June 2015) mirror refigured by Optic Wave Labs P-V WaveFront 1/14.24, Strehl Ratio 0.993 (Aug '15)
Criterion RV-6 seems to be circa 1973 (June 2015) [For Sale]
Celestron C8-A XLT (January 2015) [For Sale]
Celestron PowerSeeker 70AZ (Christmas 2014)
Aldrich Astronomical Society member since 2015
Posted 01/20/2015 12:20PM #1
Your paint spots on the deck are a good idea. If you get Polaris to correspond to the chart you should do nothing else. If a latitude scale doesn't correspond to yours...that would either be the scale is off or your mount is not quite level. Neither of those should matter---long as the whole thing doesn't tip over! PS there is an extremely accurate alignment that uses your main scope and looks for stars' drifts under high magnification. I used to do that once a year with a big observatory scope. With that you can nail the pole to within a few arc-sec if you're a fanatic like me. Totally unnecessary unless you are doing multi-hour exposures...which no one does anymore now that film is no longer used. Tom Dey

29-inch Dob in a dome
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Posted 01/21/2015 06:35AM #2
[QUOTE]Charles Stevenson said:

Cassiopeia doesn't seem to match the location in the sky in relation to where I've positioned Polaris. [QUOTE]


You should be able to rotate your polar scope within the mount. When you polar align using the polar scope, rotate the polar scope until the position of Cassiopeia and the Big Dipper are close to how they appear in the sky. For example, if you're looking at the sky and Cassiopeia is at 10:00, then the Big Dipper would be below the horizon at 4:00. Now center Polaris is the little circle.

Note that you won't improve much over what you've already done since Polaris isn't terribly far from the NCP anyway.
Posted 01/22/2015 04:29PM #3
1. You don't need to see Polaris or use the polar finder. Use the ASPA procedure in the hand control instead.

2. The mount is quite immune to goto accuracy problems caused by polar alignment. Make sure you are centering the correct stars and using up and right keys only for final centering.

Uncle Rod

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