Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Confused About Declination Setting Circle

  • Please log in to reply
16 replies to this topic

#1 SGPPV

SGPPV

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 08 Oct 2015
  • Loc: Detroit, Michigan

Posted 29 March 2020 - 04:23 PM

This is my first post, although I have been a long time reader.

 

I am using the almost constant overcast in Michigan to work on my skills finding objects in my Q 50th with the setting circles.

 

As I have attempted to use the setting circles, I am constantly confused over which part of the declination scale is positive and which is negative. I am in the northern hemisphere.

 

  1. After studying the telescope and working with it, I think the scales are signed as shown in the first attached figure. Is this correct?

    SetCircles1-shrunk.jpg
     
  2. This (if I am correct above) brings up the fact that there are two settings for a given declination, one to the left and one to the right, as shown in figures two and three, where the declination is set to +70. They are the same declination, but 12 hours apart in RA. Which setting position (direction) is correct? How do you choose?

    SetCircles2-shrunk.jpg

    SetCircles3-shrunk.jpg
     
  3. I am looking at using the vernier scale produced by munirocks. That has a "+" on one side and a "-" on the other side, which further confuses me because I am thinking that both sides contain positive and negative declinations. For example, If I am facing south (I am at about 42 degrees North Latitude) I count down from positive to zero to negative declination, all on the same side.
     
  4. The lines on the vernier scale are very small and close together, and with my age and vision it is difficult to focus well at the close distance I need to view it. Is it possible to stretch out a vernier scale so that its lines are further apart?

I look forward to your answers.

 

-- Paul



#2 msl615

msl615

    Viking 1

  • *****
  • Posts: 785
  • Joined: 07 Jun 2015
  • Loc: Fairbanks, Alaska

Posted 29 March 2020 - 05:58 PM

There is a way to do this by a basic hands on experiment, and then it will be easier later to apply the theory you have been working on.

 

Set uo the scope and then find two stars in view that are relatively close, but differ in declination.  Set the scope and the RA and DEC circles on one of them.  Then turn the scope to the RA of the second star, and noting the DEC you have set, turn the DEC axis to find the second star. That will tell you which way to read the DEC circle.  I do this each time it has been a while since I used DEC circles, and can't remember "which way is up" on the DEC circles. 

 

Let us know how you work your way through this.

 

Mike



#3 555aaa

555aaa

    Vendor (Xerxes Scientific)

  • *****
  • Vendors
  • Posts: 1,672
  • Joined: 09 Aug 2016
  • Loc: Lynnwood, WA, USA

Posted 29 March 2020 - 06:15 PM

They don't mean anything unless you are using the telescope with the polar axis (the "vertical" axis) pointed to the north celestial pole. The declination axis reads 90 when pointed at the north celestial pole. From the north pole down is always a positive number until you get to zero which is the celestial equator. If you live in the N hemisphere, you'll never see any objects with negative declination that are in the northern part of the sky; they are all below the horizon. But you can see them in the southern part of the sky. So if you have the telescope pointed N and the declination axis horizontal, as you swing the telescope it will go from being at the pole (dec = 90) to at zenith (dec=your latitude) to zero when it is on the celestial equator. All the sky below that imaginary line is at negative declination. So the circle numbers start to go back up but as negative numbers. So as I see your mark up photo, it looks correct to me.


Edited by 555aaa, 29 March 2020 - 06:15 PM.


#4 justfred

justfred

    Viking 1

  • ****-
  • Posts: 636
  • Joined: 24 Sep 2010
  • Loc: Birmingham, Alabama, USA

Posted 29 March 2020 - 09:52 PM

Hey there, Paul.

 

What kind of mount do you have?

 

Set it up in your living room in equatorial mode. Go ahead and set it for your latitude and pretend its polar aligned. Check a planetarium program for the ra and dec 8PM tonight for Capella and move the scope to that dec setting and move the scope in ra to ballpark where it should be and move the ra dial to match the setting for Capella. You're now set up to play with things. Pick some  objects and move the scope to their ra  and dec checking your planetarium program from time to time to see if it looks like its pointing where it should be. Find objects further and further to the South and note the declinations and where the OTA  is pointing. The +/- will start to make more sense.  Do this a while and then go outside at night.

 

Fred



#5 RobertPettengill

RobertPettengill

    Messenger

  • -----
  • Posts: 446
  • Joined: 06 Jan 2013
  • Loc: Austin, Texas

Posted 29 March 2020 - 11:38 PM

The declination scale is not marked because it’s interpretation depends on which hemisphere you are in when you align the scope. 

 

In Michigan you will align to the north celestial pole. This makes the 90 you use the + or north side. 
in Chile you align to the south celestial pole so the sides of the scale are interpreted in the opposite sense with the 90 on top being the south or - side. 
 


Edited by RobertPettengill, 29 March 2020 - 11:39 PM.


#6 SGPPV

SGPPV

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 08 Oct 2015
  • Loc: Detroit, Michigan

Posted 30 March 2020 - 09:47 PM

Thank you for your help and suggestions. I'm glad to see I am on the right track. In the past I thought that the 80 to one side of the 90 was positive, and the 80 on the other side was negative, whereas the switch in sign actually occurs at the 0.

 

My Q is mounted on a Gitzo tripod with an AstroTrac wedge. I use the Painless Polar Alignment procedure -- I have a 32mm Brandon and I can always see Polaris so it is indeed painless. It works really well and easily for me.

 

It looks like I may get a clear night on Thursday. I will prepare a list of targets as suggested and then practice and see if I can nail this down. 

 

-- Paul


  • JamesMStephens likes this

#7 Johninuk

Johninuk

    Sputnik

  • -----
  • Posts: 46
  • Joined: 05 Jun 2012
  • Loc: Nottingham UK

Posted 31 March 2020 - 10:24 AM

I also have the Astrotrac wedge for my Q,and have been looking at the gitzo carbon fibre tripods for easy setup and portability.What model are you using Paul.

John.

#8 Terra Nova

Terra Nova

    ISS

  • *****
  • Posts: 21,929
  • Joined: 29 May 2012
  • Loc: Under the Blue Moon of Kentucky

Posted 31 March 2020 - 10:43 AM

Frankly, I never even have thought about it. When I set up my scope and align it to the N.C.P. I have a fixed idea in my head of my celestial meridian, zenith, and celestial equator so With these spatial references, it’s just intuitive when pointing my scope to an object above (+ or N dec) or below (- or S dec) the celestial equator. I guess it just comes naturally as I’ve used setting circles for over fifty years. (I started with an Edmund German Equatorial Mount with the big black phenolic setting circles and the wonderful Sam Brown illustrated book that Edmund put out entitled Time In Astronomy, back in the summer of 1966 and that practical education just stayed with me.)


  • ETXer, rcwolpert, Optics Patent and 1 other like this

#9 SGPPV

SGPPV

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 08 Oct 2015
  • Loc: Detroit, Michigan

Posted 31 March 2020 - 11:45 PM

Terra:

 

I like the way you described your feel for the celestial sphere. I hope to develop that feel and skill in time. I started with Turn Left at Orion.

 

John:

 

I use a Gitzo G1348 MK2 carbon fiber tripod. I have been very happy with it. It is strong and stiff, and light (especially compared to the tristand). It has a flat plate instead of a rising column, which really adds to the stability. The AstroTrac wedge screws on very tightly. I tried a G1248 carbon fiber tripod with rising column first, but that wasn't stable enough. The G1348 is no longer made; it has been replaced by newer models.

 

I am considering replacing the flat plate on the tripod with a Gitzo leveling base. This will allow me to level the AstroTrac wedge without fiddling with the length of the legs.

 

I had a lightweight aluminum plate machined to mount the Q 3.5 onto the AstroTrac. Richard Taylor at AstroTrac helped me with the specifications of the mounting holes, and suggested that I remove the triangular mounting plate from the wedge and attach my plate in its place. I can leave all of this assembled for quick deployment (tripod; wedge; plate) and easily fit it into the tripod bag.

 

I put a beveled lip around the plate to match the bevel on the base of the Q. This allows me to easily place the Q into position where the lock-down screw goes into the base, and helps hold it in place will tightening it down.

 

Mounting-1-min.JPG


  • Terra Nova likes this

#10 SGPPV

SGPPV

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 08 Oct 2015
  • Loc: Detroit, Michigan

Posted 31 March 2020 - 11:46 PM

A few more pictures:

 

Mounting-2-min.JPG

 

Mounting-3-min.JPG


  • Rick McNelly, Steve C., Kevin Barker and 2 others like this

#11 Johninuk

Johninuk

    Sputnik

  • -----
  • Posts: 46
  • Joined: 05 Jun 2012
  • Loc: Nottingham UK

Posted 01 April 2020 - 04:52 AM

Thanks Paul for info.I have used a 8mm thick Ali plate on mine and screwed it direct to Astrotrac wedge as you have. I wasn't aware Gitzo produced a leveling plate.Thats interesting.
John.

#12 munirocks

munirocks

    Viking 1

  • *****
  • Posts: 582
  • Joined: 21 Oct 2013
  • Loc: Bourne End, UK

Posted 09 April 2020 - 05:46 PM

The + and - sides of the Vernier tell you which side of the double-sided Vernier to use. That is, when pointing the scope at targets with a positive Dec value (north of the celestial equator) you use the 0 point and the + side of the Vernier. When pointing the scope at targets with negative Dec values (low in the south, south of the celestial equator) you use the 0 point and the - side of the Vernier. 

 

The + and - marks on the Vernier also indicate the direction of + and - Declination, but only when used relative to 0 Declination; that is, in the first positive quadrant above 0 and the first negative quadrant below zero. Don't try to find meaning in them "over the top" when they straddle 90 because in this position they are meaningless. 

It might be easier to understand if you ignore the half if the Dec circle that doesn't get used and only think of the side that does get used. That's the side that the eyepiece is on, between +90 and -90.

 

As for designing a longer Vernier, it is possible to make one that engages with the main scale every 5 or 10 marks. I'll have a think about it. I'm intrigued.



#13 SGPPV

SGPPV

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 08 Oct 2015
  • Loc: Detroit, Michigan

Posted 09 April 2020 - 06:56 PM

Thank you for your excellent explanation, now it makes sense. I was indeed thinking of it relative to the top at 90 rather than at 0, and as a direction to move rather than which direction to read the scale.

 

I found a description of an extended vernier on the web at:

 

        https://books.google.com/books?id=EM-sLyVmMwIC&pg=PA14&lpg=PA14&dq=%22extended+vernier%22&source=bl&ots=JJGEKcTGtE&sig=ACfU3U3CBo2ObS1CHjjcAgcHJMXHMdBFaA&hl=en&sa=X&ved=2ahUKEwjsh_CI8sjoAhVMZM0KHYsYAcwQ6AEwDXoECA0QKA#v=onepage&q=%22extended%20vernier%22&f=false

 

This is a scale where the divisions on the vernier are twice the size of the divisions on the main scale, and n divisions on the vernier equal (2n-1) divisions on the main scale.

 

They also show a double-folded vernier, which shortens the length of a double vernier. I don't know if you could use this with an extended vernier. If this is possible I think it would be easier to illuminate and see under dim light.

 

-- Paul



#14 munirocks

munirocks

    Viking 1

  • *****
  • Posts: 582
  • Joined: 21 Oct 2013
  • Loc: Bourne End, UK

Posted 10 April 2020 - 03:11 AM

Very nice plate. I would suggest a much longer center bolt going into the base of the Q, especially if you have a 50th scope with Powerguide. With a recessed hole in the Q base a standard tripod bolt won't even reach the hole. How many threads are actually engaging? If you can't find a longer one the right length you can make your own; look up "universal bolt" over in the equipment forum. The bolt I use extends 9 threads (9/20 of an inch) above the plate.


Edited by munirocks, 10 April 2020 - 03:34 AM.


#15 Optics Patent

Optics Patent

    Surveyor 1

  • *****
  • Posts: 1,999
  • Joined: 30 Oct 2016
  • Loc: Dallas TX

Posted 10 April 2020 - 08:49 AM

Smart to always consider number of threads engaged.  Easy to verify turns from first engagement (or turns to disengagement). 

 

For low stress applications like an under 10-pound scope not subject to loads or impulses, strength isn't an issue, so 3-4 threads should be fine.  Another rule of thumb might be the screw diameter (1/4" = 5 threads @ 20/inch).  More than that is probably a waste.


  • NC Startrekker likes this

#16 SGPPV

SGPPV

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 08 Oct 2015
  • Loc: Detroit, Michigan

Posted 11 April 2020 - 03:53 PM

Thanks.

 

The pictures don't show a good view of the center bolt. It has an un-threaded part between the threads and the knob that accommodates the recess on the base, and also allows the bolt to sink down part way into the plate so I can place the base of the Q fully flat on the plate without having to unscrew the bolt.

 

I just checked it and it engages a full 4 threads. The beveled lip of the plate holds the Q firmly in place, so I don't think there is much lateral force on the bolt. 

 

-- Paul



#17 munirocks

munirocks

    Viking 1

  • *****
  • Posts: 582
  • Joined: 21 Oct 2013
  • Loc: Bourne End, UK

Posted 13 April 2020 - 05:29 PM

Thanks for the info. That's put my mind at rest.


  • SGPPV likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics