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Scratching my head, am I st*pid?

Polar Alignment
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#1 Monk80

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Posted 11 June 2021 - 09:48 AM

Hi All,

 

I've changed from an AltAz to a EQ (CGEM) mount not too long ago so inevitably I'd had to run in some questions sooner or later.

I "thought" I had the polar alignment thing right, turns out slewing to deep sky objects did not work satisfactory. The polar scope itself needed calibrating, for which I found a very helpful YT tutorial. It's fine now. But it actually left me scratching my head still.

 

I compared the position of the NCP in relation to Polaris in Stellarium with that of the image through the polar scope around the same time (Cassiopeia dialed into the same position/time/date) It appears as if those two are 180º off.

 

-Stellarium has the NCP above Polaris at date/time 'X' 

-The polar scope reticle shows NCP below Polaris at same date/time 'X' 

-In both cases Cassiopeia is at approximately 05:30 Hrs positioned of the NCP. (So below the NCP but rotated around NCP ± 20º CCW

 

This seems really odd to me and confuses me. How is it possible? I get the idea that my pointing and tracking errors are due to the fact that I am aligning to the NCP on the (180º) opposite of Polaris.

 

Please find attached pictures of what I mean: an image of the sky today at 00:00hrs and the view through the polar scope dialed to the same "time". One can see NCP is 180º off.. I thought of optically reversed image but that does not count as it relates to its orientation to i.e. Cassiopeia.

 

Scratching my head is Stellarium wrong? ..Hhmm prolly not. Is my polar scope wrong? Prolly not.. I'm wrong.. but how???

 

Anyone care to enlighten the confused man ? I added the images of what I am seeing to this post.

 

 

Thanx a bunch in advance everyone :)

 

CS

Monk

 

 

  

 

Attached Thumbnails

  • Stellarium.jpg
  • Polarscope.jpg


#2 Stu Todd

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Posted 11 June 2021 - 09:55 AM

Reading very quickly through, if the things you are expecting to see are 180 degrees out, then maybe your time of observer is 12 hours out? You using 24 hour clock?

 

I don't want to insult you, just the obvious things are good to discount from the mix.


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#3 Monk80

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Posted 11 June 2021 - 10:00 AM

No insult taken, lets get the obvious wrongs out:

 

-the time and place of observer are correct in Stellarium: date of today, correct lat/long, 00:00 hrs

 

Which correlate with my observation spot/time yes 24H system in Stellarium, I fast forward to 00:00 hrs to compare to what I see in the polar finder at the same time.

 

hence my confusion it still being off..

 

edit: actually comparing the two images i attached already expose the discrepancy..

Reading very quickly through, if the things you are expecting to see are 180 degrees out, then maybe your time of observer is 12 hours out? You using 24 hour clock?

 

I don't want to insult you, just the obvious things are good to discount from the mix.


Edited by Monk80, 11 June 2021 - 10:02 AM.


#4 larryjh

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Posted 11 June 2021 - 10:08 AM

The polar scope is a refractor, so it turns the image upside down?


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#5 WarmWeatherGuy

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Posted 11 June 2021 - 10:09 AM

When you look through the PAS everything is upside-down. The FOV is too small to see the big dipper or Cassiopeia. The cartoon drawing of the big dipper and Cassiopeia are flipped 180° because what you see is upside-down. For this discussion let's say that the big dipper is at the 12:00 o'clock position, i.e. above Polaris, then you want the cartoon of the big dipper to be at the 12:00 o'clock position, but the stars you see in the PAS will be upside-down. If you could see the big dipper while looking through the PAS you would see it at the 6:00 o'clock position.


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#6 Astrojensen

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Posted 11 June 2021 - 10:09 AM

The polar scope is a simple keplerian telescope, so it turns things 180°, compared to the naked eye.

 

 

Clear skies!

Thomas, Denmark


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#7 Monk80

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Posted 11 June 2021 - 10:14 AM

Ah I get it the cartoon Cassiopeia is drawn in the "wrong" position just to make the adjusting process workable or lining it up to the right position according to NCP.
I thought of the refractor lens effect, but the artificial arrangement of the graphics in the Polariscope turns out where I lost the trail..

Thanks for clearing that up!


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