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

Estimating Position Angle

  • Please log in to reply
15 replies to this topic

#1 rugby

rugby

    Vostok 1

  • -----
  • topic starter
  • Posts: 120
  • Joined: 17 Dec 2018

Posted 27 September 2019 - 09:15 AM

Estimating position angle, for me, is a challenge. Despite being able to see a companion clearly I often miss the angle by twenty percent or more! I have taken to describing quadrants, like north-preceeding or south-following , instead. Makes me feel better about myself knowing I am in the right neighbourhood even though I am at the wrong house.

What can I do to turn this weakness around and make it a strength? Maybe, however, it is not a weakness at all. I would like ask others their experiece estimating PA. Then I want to post a list of ten pairs that shows magnitudes and separation but not angle. Enthusiasts would have to observe each pair, guess the PA, and forward the results to CN. 

Let me know if you would like to try this test along with any suggestions to make the process work smoothly.



#2 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6608
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted 27 September 2019 - 09:43 AM

I am usually off by about 20 deg on close pairs but that’s in the ball park.

#3 TOMDEY

TOMDEY

    Aurora

  • *****
  • Posts: 4664
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 27 September 2019 - 10:03 AM

Hi, rugby! Are you using an eyepiece with a reticule? You rotate/line it up with the drift direction and then the pair's axis. The difference gives the angle of interest. Simple cobbled angular scale on the eyep/focuser interface gives the numbers. Do that several times, and report the average and standard deviation. That works quite well and requires no special fancy equipment. 

 

The next step up would be a fancy filar eyepiece, with traveling web, comfortable tracking mount, etc. Lots of precise microscope such can be found used, cheap! I have a few B&L ancient ones that work nicely.    Tom



#4 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6608
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted 27 September 2019 - 10:18 AM

I have resisted the micrometer EP, because they are not available as premium eyepieces.  It would be nice to see a Delite 5mm or ES 82 deg LER equivalent with a reticle, scale, and illuminator.  The eyepieces available are not up to a premium standard, IMO.

 

I've observed enough doubles that I can estimate distance fairly well qualitatively, but of course not up to a quantitative accuracy.


Edited by John Fitzgerald, 27 September 2019 - 10:24 AM.


#5 fred1871

fred1871

    Apollo

  • -----
  • Posts: 1485
  • Joined: 22 Mar 2009
  • Loc: Australia

Posted 28 September 2019 - 12:36 AM

I am usually off by about 20 deg on close pairs but that’s in the ball park.

Yep. The closer they are, the harder to make an accurate estimate of angle. Not enough separation to work with, unless you go to very high powers. That of course has its limits. Pairs below full resolution, only elongated with the particular aperture, remain rough estimations.



#6 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6608
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted 30 September 2019 - 09:51 AM

Last evening I did a somewhat qualitative experiment with some doubles in Cygnus on estimating PA.  I did not know the PA beforehand, but looked it up in the WDS catalog later.  This was done with my 6" eq mounted triplet.  All PA estimates were done by eye only.  No reticles or scales were used.  Magnifications were either 173x or 243x depending on separation.  Seeing was variable from 2/5 to 4/5.  I had to watch and wait for a few seconds of good seeing on some of these.

 

Here are the results given as STF designation, mag1, mag2, separation", estimated PA in parenthesis, actual PA from WDS.

 

2522, 7.7,8.8,4.5",(340),339

2534, 8.2,8.4,7.0",(50),63

2555, 9.4,9.9,1.8",(270),283

2557, 7.5,10.2,11.0",(100),103

2609, 6.7,7.6,1.8",(40),23

2610, 8.8,9.2,4.3",(300),296

2611, 8.5,8.5,5.1",(200),208

2645, 8.6,9.0,1.6",(150),139

2657, 7.3,7.6,1.0",(180),171

2702, 8.7,9.0,3.2",(240),206

2711, 8.2,9.2,.2.4"(250)223

2726, 4.3,9.5,6.6",(90),70

2746, 7.9,8.7,1.2",(330),323

2757, 7.8,9.2,1.9",(270),264

2773, 8.5,9.1,3.3",(110)113

 

These are mostly accurate enough to confirm seeing the double well enough, IMO.

 

Average error was about 11 degrees on these 15 samples, certainly not good enough for much, but confirming a sighting.


Edited by John Fitzgerald, 30 September 2019 - 05:12 PM.

  • rugby and Astrolog like this

#7 rugby

rugby

    Vostok 1

  • -----
  • topic starter
  • Posts: 120
  • Joined: 17 Dec 2018

Posted 30 September 2019 - 05:11 PM

An excellent list John. I will work on it tonight



#8 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6608
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted 30 September 2019 - 10:03 PM

Did eleven more examples tonight, and my average estimate was off about 8 degrees.  I need some kind of external scale around the eyepiece, I guess.



#9 gregj888

gregj888

    Vanguard

  • -----
  • Posts: 2288
  • Joined: 26 Mar 2006
  • Loc: Oregon

Posted 30 September 2019 - 10:45 PM

If you pull up some of the orbital plots from WDS 6th orbital catalog it will give you some idea of the different methods and how accurate they are.

 

 https://ad.usno.navy...00063 5826a.png

 

The green are visual.  Visual include newbies to seasoned pros but there is a lot of variance.  As you move to photographic things improve, then speckle then some of the new interferometric observations of close doubles.

 

Visual is great to learn and fun.  If you want accuracy, look into speckle.   Speckle Tool Box and  Reduc are both free and a 290 base mono uncooled cameras are $369 US for ASI and $329 for QHY.    


  • rugby likes this

#10 rugby

rugby

    Vostok 1

  • -----
  • topic starter
  • Posts: 120
  • Joined: 17 Dec 2018

Posted 30 September 2019 - 11:35 PM

Here are my results from Sept 30. 

                           est

STF 2522 339    335

STF 2534  63     37

STF  2557 103   110

 

I searched for STF2609 but did not find it.  Spent about 2.5 hours on this meagre list. Working at or near the zenith takes time. 

Are others using GOTO ?



#11 rugby

rugby

    Vostok 1

  • -----
  • topic starter
  • Posts: 120
  • Joined: 17 Dec 2018

Posted 01 October 2019 - 08:23 AM

I find by increasing the power the pair moves through the field rapidly thus making the PA estimate easier



#12 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6608
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted 01 October 2019 - 09:48 AM

I am using a driven scope. I use the hand controller to move the double north and south in the field to establish direction. Nexus DSC.
  • R Botero and rugby like this

#13 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6608
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted 02 October 2019 - 10:21 PM

I have observed and estimated PA  for 37 more doubles the past three nights, and now, with intense practice at the eyepiece, have my estimated PA average error down to about 7 degrees. I think that's about as good as I can do without some kind of graduated device.


Edited by John Fitzgerald, 02 October 2019 - 10:21 PM.

  • Nucleophile and rugby like this

#14 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6608
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted 03 October 2019 - 10:46 PM

Observed 18 more doubles tonight, no improvement in estimating PA.  Still stuck at an average of 7-8 degrees error.  I wish there was a graduated reticle that would work in a TV Delite or Pentax XW eyepiece.


  • rugby likes this

#15 rugby

rugby

    Vostok 1

  • -----
  • topic starter
  • Posts: 120
  • Joined: 17 Dec 2018

Posted Today, 09:36 AM

John      At what power do you make the estimates?



#16 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6608
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted Today, 09:49 AM

John      At what power do you make the estimates?

Depends on separation. Usually 173 or 243x.


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