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Making a model with limited sky visibiltiy.

 

My G11 is my "backyard" setup with a Celestron 9.25" Edge HD OTA.? I have limited visibility due to proximity to my garage and tall trees nearby.? When I ask for "help making a model" I can't see many of the bright stars, so I have never been able to use the "go-to" features at all since there is no way for me to tell the mount where it's pointing.? Is there a workaround???
 

The goto feature works even without building a model, it will just not be very accurate but will slew the mount to the general vicinity of your intended target. After that initial slew you simply nudge the mount with your hand controller the last few degrees to finish centering your target.
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If you are intent on building the model regardless, then just search for the stars that are actually visible and use those. You can press GOTO->BRIGHT STAR and then press the up/down arrows to search for the star, center it in your field of view with the HC and then from the main menu go to ALIGN->ALIGNMENT.
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If the stars used are nearby to each other the model will only be accurate within that area but, then again, that’s the only area you have visibility over so you should be fine
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If, on then other hand, you’re imaging, you don’t really need to build a model. Simply tell your imaging software to “slew and center” your target. It will do the initial slew, take a picture, plate solve, sync the mount to the correct current coordinates, determine where it needs to move and by how much and do a second slew. Rinse and repeat as needed. All without user intervention beyond the “slew and center” command :)
 

On Wed, Mar 26, 2025 at 11:50 AM, David Woolf wrote:
I have limited visibility
With the HC (L6/1.6) you can use the mount to select your stars.? Say I set the mount to CWD and Cold Start, then I want to use a visible bright star.? ?Slew the mount manually to point the OTA at the star, well generally near or I use the finder.? Press Menu->Identify and select the BSL catalogue.? That returns a list of stars sorted by how close within the list the OTA points.? This BSL-star will be the top or closest bright star that the telescope points at.? GoTo that selection and center in the eyepiece.? Enter Menu->Model->Alignment for the 1-star alignment and synchronization.
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Then I slew to another star if desired, picking good placements.? Remembering we want them separated over the extended quadrant as well as possible for a given model side because any error centering on the cross hairs magnifies as the calculated circles extend to the galactic pole.? (A bad model works exactly like a good model, in a like manner).? So, if the OTA allows, reach across the meridian without changing saddle sides (without flipping) use these stars too as needed.? Visually we need good polar alignment with a 1-star alignment per side.? Or near polar alignment (<a few degrees) with three-to-five-star alignment on a side.
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Regardless of good or a so-so alignment, as mentioned I too always synchronize on a local star near where any target resides.? Again, IDENTIFY can be used to sync and center reliably.
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Doug
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For what it’s worth…

I’ve had my G11 for slightly less than a year now, after years of having Celestron GEMs. The G11 on a permanent pier.
Like with your situation, my sky is limited by my garage and tall trees. Here’s what I did to get to get decent go-tos.

  1. In the daytime I used a ‘carpenter’s level’ app on my phone to set the tilt of the saddle equal to my latitude, then I used a solar app to set the mount pointing due north at local noon. This gave me a rough polar alignment.
  2. I don’t have a polarscope, but at night I was able to see Polaris through tree branches, so I eyeballed through the polar axis to tweak the mount to center Polaris.
  3. I could see a few bright stars, so I then used the ‘Polar Alignment Correction’ app in the Gemini II to further tweak the PA. (Scott Losmandy has a video describing this procedure on the Losmandy YouTube channel.)
  4. After a few months of use I could tell that the PA still wasn’t great so I ran the ‘Drift Alignment’ routine in PHD2. This worked quite well even with my very limited sky.

So now I do a 1-star synchronization on a bright star at the start of each night and then my automatic go-tos are pretty close. Occassionally I need to use platesolving to center the mount. For this I use the DSLR astrophotography software BYE/BYN along with ASTAP and Carts du Ciel.

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Another option, if your polar alignment is roughly ok, is to go to a bright star near the object you want to observe, then do ‘Model/ Synchronize’ on the HC. This will improve any go-tos you do in that part of the sky.

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