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Polar Alignment

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Polar Alignment

Posted by Norman Lavender at 17:49 on 2011 Mar 11

In "Turn Left at Orion" "How to Run a Telescope" refers to setting the equatorial axis as "It is tilted at an angle of 90 degrees minus the latitude where you're observing"Is this correct, I thought you set it to the latitude. Have I missed something here?As I have high trees to the north of my garden I am relying on the latitude setting for approximate alignment.

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Re:Polar Alignment

Posted by Roy Hughes at 12:32 on 2011 Mar 12

SkyMap has alpha UMi at Dec 0 degrees and altitude +52 degrees from London so+52 deg. ( = latitude) up from the N horizon seems right.I've just stuck a clinometer on my equatorial (set up 35 years ago!) and confirmed it.

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Re:Polar Alignment

Posted by Norman Lavender at 17:36 on 2011 Mar 12

Thank you Roy. So are you confirming that the statement in "Turn Left at Orion" is incorrect?

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Re:Polar Alignment

Posted by Norman Lavender at 18:07 on 2011 Mar 12

Thank you Roy. So are you confirming that the statement in "Turn Left at Orion" is incorrect:

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Re:Polar Alignment

Posted by Norman Lavender at 18:07 on 2011 Mar 12

Thank you Roy. So are you confirming that the statement in "Turn Left at Orion" is incorrect:

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Re:Polar Alignment

Posted by Norman Lavender at 19:34 on 2011 Mar 12

I don't know why my last post got repeated 3 times? I hope it doesn't happen again.

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Re:Polar Alignment

Posted by Callum Potter at 21:43 on 2011 Mar 12

Question is (in the book), does it mean relative to horizontal or vertical ?Callum

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Re:Polar Alignment

Posted by Andrea Tasselli at 21:58 on 2011 Mar 12

Actually I think that it is relative to the position you measure the angle from. If it is from the zenith then the angle is 90-lat.Andrea T.

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Re:Polar Alignment

Posted by Norman Lavender at 07:12 on 2011 Mar 13

Thank you Callum and Andrea.Having re-read the statement in the book it does follow on from a description of the alt-azimuth mount and describes the equatorial mount as an alt-azimuth tipped over. From that point of view it would appear it is indeed talking about measurement from the zenith.However for a novice this is a bit confusing as in most descriptions of polar alignment (i.e. in Norton's Star Atlas") explicitly refers to the angle relative to the horizontal.

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Re:Polar Alignment

Posted by Nick Atkinson at 18:41 on 2011 Mar 19

My problem is a slight orthagonal differance from the mount and the telescope. This is detected by picking a star on the meridian and changing the telescope from side to side. This is achieved by adjusting the clock by plus or minus one hour.Any dispacement in RA is a measure of this. I have been intending to shim up the mounting plates but have never got round to this. Once done it should improvove both the pointing accuracy and guiding.Must get this done but I have a 50 -50 chance of chosing the right end!

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Re:Polar Alignment

Posted by David Arditti at 17:51 on 2011 Mar 21

Nick's problem will only apply if you regularly GOTO on opposite sides of the mount. If you stick mostly to one side, as I do, adjusting the clock or time displacement so you don't swap sides, there will be no effect from non-orthogonality of the mount. If you do swap, there will be an effect on pointing accuracy (though many telescopes have major pointing effects from shifting optics/collimation as well). So far as I can see, there will never be an effect on tracking accuracy (what I presume Nick means by "guiding"), provided the mount is correctly polar aligned.David