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Stellarium Accuracy with Evolution Mount

cassegrain Celestron planetarium software SCT
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#1 sandconp

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Posted 05 September 2019 - 10:55 AM

I noticed when I use Stellarium and Stellarium Scope using the Prolific and ASCOM drivers with a cable from my PC to the bottom of Star Sense Hand control my accuracy seems to be a bit off. I perform the Star Sense alignment using the Celestron telescope and perform a calibrate to center the star and then perform another re-alignment and when I use the SS hand control to target the star, it's dead center. But when I use Stellarium along with Stellarium scope to target the star, it's not centered and off to the left corner in my eyepiece. I always perform an SS Auto Alignment before I plug in the cable from the PC to the hand control.

Any ideas what is causing this issue? It's like Stellarium is not picking up the new calibrate values from the Star Sense hand control.

 

My telescope is a Celestron Evolution 8 using Stare Sense with a ALT-Z Mount



#2 Jeff Struve

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Posted 05 September 2019 - 11:44 AM

I use Stellarium/StellariumScope with ASCOM and EQMOD and GoTO's are dead on... I use Stellariums alignment routine via ASCOM/EQMOD.... maybe thats the difference? 



#3 3snows

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Posted 05 September 2019 - 12:25 PM

I've had similar problems in the past and it turned out to be that the clocks were not synced.  Check that your mount and computer clocks are synced.



#4 sandconp

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Posted 05 September 2019 - 01:36 PM

I use Stellarium/StellariumScope with ASCOM and EQMOD and GoTO's are dead on... I use Stellariums alignment routine via ASCOM/EQMOD.... maybe thats the difference?


I of course use the ASCOM drivers but what is ASCOM/EQMOD and how do I change that in my setup?

Edited by sandconp, 05 September 2019 - 01:36 PM.


#5 sandconp

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Posted 05 September 2019 - 01:40 PM

I've had similar problems in the past and it turned out to be that the clocks were not synced.  Check that your mount and computer clocks are synced.


That's a good point I never thought of that. I use the Celestron GPS with the SS Hand Control and I am assuming that time should be very accurate. How would I change Stellarium on my PC to use my GPS to get the exact time or would I have to go into Windows 10 and change the time to match what the GPS and or the hand control?

It must be very close but not close enough because when I am Imaging, I need these dead center.

#6 SkipW

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Posted 05 September 2019 - 02:41 PM

Stellarium defaults to sending RA and Dec relative to the equator and equinox of J2000. A lot of telescopes expect to get RA and Dec in terms of the E&E of the current date ("JNow"). Try changing this in the configuration settings for your telescope and see if it fixes the problem.



#7 SkipW

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Posted 05 September 2019 - 02:51 PM

Also, I wouldn't expect clock synchronization to be an issue at all except for the moon or other solar system objects, and then only at some times. Since stars and DSOs don't change RA and Dec at all for practical purposes, clock synchronization shouldn't be an issue for these unless the clocks disagree by a decade or more. 


Edited by SkipW, 05 September 2019 - 03:22 PM.


#8 Michael_Swanson

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Posted 06 September 2019 - 07:31 AM

SkipW is right about clock sync - not an issue for DSOs as Stellarium is sending RA-Dec which doesn't change according to minutes of time.  But, it does change across many years which is why the hand control (HC) uses JNow coordinates.  If Stellarium is using J2000 coordinates, that is now almost 20 years of precession error.  I don't use Stellarium but you might poke around in the settings/documentation to see if it uses JNow or J2000 coordinates and whether you can change to JNow.  

 

To test this theory in the field - issue a GoTo using the StarSense HC.  Then on the HC press MENU, scroll to View/Goto Pos. and press ENTER.  The HC will display the coordinates it believes are centered in the eyepiece.  Make a note (snap a pic).  Then, GoTo that same object in Stellarium and see what coordinates the HC now displays.  That would be the coordinates Stellarium sent to the scope.  Compare the two sets of coordinates and you might have your answer.

 

One note for technical accuracy - if you GoTo an area of the sky where the GoTo Approach direction is opposite the direction of tracking movement, anti-backlash will engage right after the GoTo finishes and so the actual coordinates displayed would not be the precise coordinates the scope drove to.  But, this behavior will be consistent for GoTos via both the HC and Stellarium so the comparison in the previous paragraph is always valid.

 

Best regards,
Mike Swanson
Author of "The NexStar User's Guide II"
Author of "The NexStar User's Guide"
Author of "NexStar Observer List"
https://www.NexStarSite.com


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#9 dcollier

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Posted 06 September 2019 - 08:15 AM

Mike-

 

I use Stellarium.  What he is describing is most likely caused by J2000 vs. Jnow.  I do not have issues when using Jnow with Starsence. 

 

          -Dave 



#10 sandconp

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Posted 06 September 2019 - 11:16 AM

I checked my Stellarium Scope settings and I indeed have the J2000 option checked. I had an issue connecting to the scope from PC about a month ago and I was messing with my settings and I must of clicked the box for J2000.

So it sounds like uncheck J2000 and click on Jnow? I really don’t recall what the default was.

I know that I have use it before and it was always spot on so that has to be the issue.

#11 Michael_Swanson

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Posted 06 September 2019 - 11:16 PM

Correct - you want to use JNow with Celestron scopes as the HC converts its internal database coordinates to JNow automatically (as I recall you don't see it in the object info but you do see it as the coordinates displayed after a GoTo).

 

Best regards,
Mike Swanson
Author of "The NexStar User's Guide II"
Author of "The NexStar User's Guide"
Author of "NexStar Observer List"
https://www.NexStarSite.com



#12 sandconp

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Posted 07 September 2019 - 01:48 AM

Correct - you want to use JNow with Celestron scopes as the HC converts its internal database coordinates to JNow automatically (as I recall you don't see it in the object info but you do see it as the coordinates displayed after a GoTo).

 

Best regards,
Mike Swanson
Author of "The NexStar User's Guide II"
Author of "The NexStar User's Guide"
Author of "NexStar Observer List"
https://www.NexStarSite.com

Went out last night to test and JNow took care of my issue.  Thanks for the input.


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