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HOW to pick stars for alignment/modeling?

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11 replies to this topic

#1 RazorbackWatcher

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Posted 24 January 2023 - 10:07 PM

I'm working with a Losmandy G11 Gemini 1

This is my first TRUE EQ mount. (go big or go home)

 

Not sure if this is a dummy question or not. 

 

I understand the theory behind modeling and using stars as a reference to build an accurate model.

I know what a star chart is and how to read one. I understand a lot of the concepts of astronomy: Earth rotation, celestial and terrestrial poles, etc. Meridian is something I'm working to understand better: imaginary line running North and South through the observers zenith?

I think I understand the workflow and the equipment.

What I'm struggling with is the APPLICATION.

 

How do I know which stars to select?

How do I CHOOSE which stars to select for alignment?

 

Mike


Edited by RazorbackWatcher, 24 January 2023 - 10:15 PM.


#2 csa/montana

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Posted 25 January 2023 - 12:02 AM

Moved to Mounts, for better fit of question.



#3 terrypaula

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Posted 25 January 2023 - 12:18 AM

Pick the bright stars



#4 Patrick

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Posted 25 January 2023 - 02:02 AM

I'm working with a Losmandy G11 Gemini 1

This is my first TRUE EQ mount. (go big or go home)

 

Not sure if this is a dummy question or not. 

 

I understand the theory behind modeling and using stars as a reference to build an accurate model.

I know what a star chart is and how to read one. I understand a lot of the concepts of astronomy: Earth rotation, celestial and terrestrial poles, etc. Meridian is something I'm working to understand better: imaginary line running North and South through the observers zenith?

I think I understand the workflow and the equipment.

What I'm struggling with is the APPLICATION.

 

How do I know which stars to select?

How do I CHOOSE which stars to select for alignment?

 

Mike

As noted, chose the bright ones.  But I will add, it's important to know the names of those stars.  So, knowing reference objects like constellations and the bright stars within them is very helpful.  If you just know the constellation, then you can look it up on a chart. 

 

But really, just whip out your phone with your Star Atlas app, and ask that what the star name it...Done!

 

Patrick



#5 dnayakan

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Posted 25 January 2023 - 06:16 AM

I think the general rules would be to pick 1) bright stars which are 2) well separated in the sky. The more the number of alignment objects you use, the more accurate the map the computer can build. Cheers, DJ


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#6 michael8554

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Posted 25 January 2023 - 07:12 AM

Hi Mike

 

According to the User Manual:

 

"Choose 3 to 5 alignment stars from the Alignment Star List (see Appendix 8.3)

which are on the same side of the meridian and are well separated in RA."


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#7 jp071848

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Posted 25 January 2023 - 07:43 AM

Hi Mike...

 

If you haven't already done so, I would suggest that you join the Losmandy Groups.io forum. LOTS of very knowledgeable experts over there, very active and helpful. Brian Valente from Losmandy is also a very regular poster over there.

 

https://groups.io/g/...dy_users/topics



#8 KOstar

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Posted 25 January 2023 - 07:13 PM

Hi Mike

 

According to the User Manual:

 

"Choose 3 to 5 alignment stars from the Alignment Star List (see Appendix 8.3)

which are on the same side of the meridian and are well separated in RA."

Agree with the comment from michael8554.  Your question certainly is not a dummy one.

 

Losmandy is very specific when it states that the initial modeling stars should be separated by at least 2 hours in RA.  They cite an example where a star in the northwestern part of the sky looks to be far away from a star in the southwestern sky but their RA could be very close so not a good modeling choice when used together.   Also select brighter stars that you are able to easily identify.  I usually use a planetarium program like Stellarium to decide which stars I will align on for that evening.

One thing I found is that there are a LOT of Losmandy mount instructions on the internet that are outdated; particularly regarding the format for date and time entry as well as time zone offset.

 

Clear Skies!

KO



#9 John Fitzgerald

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Posted 25 January 2023 - 07:21 PM

I, too, have a G11.  Pick two stars within 40 degrees of the equator, and well separated in RA, that you can get to WITHOUT doing a meridian flip.  Doing a flip during alignment has a high probability of introducing errors.



#10 RazorbackWatcher

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Posted 25 January 2023 - 08:05 PM

Thank you for the responses.

I understand the instructions. Its the application that I'm having a difficult time.

How do I pick which stars to use? I understand that they need to be on the same side of the meridian. The list of bright stars that is provided by Genimi doesn't really specify which stars are on what side. It DOES indicate with constellation they are associated with. I guess this is where my knowledge of the night sky needs to improve. It would be nice if I could go into the process KNOWING which stars I want to use.

 

I've asked the user groups if there is a way to extract the 169 stars that are in the 'Bright Stars' catalog.

 

It would be nice if Gemini could would categorize them by hemisphere. 

 

Maybe I'm just over thinking this too much.

 

mike



#11 Inkie

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Posted 25 January 2023 - 08:44 PM

1. Yes, you really ought to have your own small library of memorized star names, their constellation association and designation, and where to point to if someone asks you to show them where they are.  I figure that across four seasons something like 12-15 stars should suffice, but I'll bet you could get away with only 8-10 for alignment purposes;

 

2. If the seeing permits, and you're visually inclined or limited to using pointing techniques (using red dot/laser pointers, guide scopes, alignment scopes, or just sighting along the optical tube and praying), it should always be easy to choose any two stars separated by about 3 hours and also by 30 degrees of declination or more.  RA and declination cover a wide expanse of sky with just three or four hours, or +/- 40 deg in the visible sky above you; and

 

3. Coming back full circle, means that the sky presented to you on any one relatively clear night should look familiar.  If you learn the constellations or asterisms, and can see their two brightest stars, and know what the catalogue is likely to call them when you run through the choices, it will become as easy as clicking on one you can see with sufficient separation from any other you're likely to use...AND that is also visible. 


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#12 RazorbackWatcher

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Posted 25 January 2023 - 08:49 PM

FWIW The list of stars is an appendices in the Gemini instructions.

I just over looked them. 


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