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Do you ever do astronomic azimuths Poll is created on January 10, 2020 5:56 am

  
  
  
  
  

Astronomic Azimuths  

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John Hamilton
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The thread about the open traverse made me wonder if astronomic observations for azimuth is becoming a lost technique. I know a few people on here who them, some just for fun like me (haven't needed to do one for a few years now)

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Bill93
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I probably shouldn't have voted because I'm not in the business, but did because I've done Polaris shots for projects in the past.

My most recent one was a bit different. The amateur astronomy club in the area is installing a better telescope in one of their domes (donated by a university that was done with it). It is big enough it had to be set in by a crane. The base is different from the previous one and needed a large adapter built to mount it.  The base has to be aligned within a couple degrees of cardinal direction in order to be in range of final alignment.

We saw no practical way to bring in azimuth from outside up a circular stair, a magnetic compass couldn't be trusted inside the steel walls, and you couldn't see the ground outside from standing height. So I did a Polaris sight in the dome to establish a north-south line on the floor.

I used SPADE for my data, checked with Stellarium which agreed well enough for the purpose, and later by MICA which was quite close to SPADE.

That was quite an experience working in a cluttered and cramped 12 ft diameter enclosure in the dark with other equipment, a bench, and people moving around and twice bumping my tripod.

Our guess at north was off enough Polaris was not visible through the opening in the done until dark enough to see it with the naked eye and the dome turned. I was getting pretty frustrated that I couldn't get az, el, and focus to happen on the star. My focus ring has enough slop that an infinity mark isn't quite good enough.

We determined the old bolts in the concrete were indeed cardinal enough the adapter could use them for reference, a fact they had no prior reason to rely on.

The telescope is now mounted. The next challenge, after they get the control circuitry and software working, will be to finish the alignment so it is truly equatorial and accurately tracks a star.

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Bill93
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Posted by: @bill93

In case anyone is interested, here is the site:

https://www.cedar-astronomers.org/pal-dows-observatory

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A friend's son welded the mounting adapter, which is a very heavy aluminum structure:

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MightyMoe
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I did them so frequently that it was part of the work flow.

My last one was in the early 2000's in a mountain canyon where GPS couldn't get a good fix.

By that time the program I had loaded up in my old DC for doing them, plotting the lat, long, updating time on the DC, and pushing a button as you observed the leading and trailing edges, was long gone and I had to do it by hand, some time later with better GPS I found out that I was about 30" off, which I was very happy with.

It's like dunking a basketball, it's been 13 or so years since I did, don't need to do it again (well,,,,, at least I can do a solar).

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John Hamilton
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When I first started doing GPS, there was a limited time window, and we couldn't do more than a couple of static sessions a day. So we set azimuth marks with polaris observations. One project I remember well was Prince William County in VA, I did 80 second order azimuths for 80 stations in a GPS blue book project using a Wild T3, in 1986 or 1987. I would observe GPS in the day on a 3 or 5 man crew, then go out at night if it was clear and observe astro's. I was on salary for the GPS, but they were paying me extra for the astro's. I could do up to 5 a night (16 positions) by myself, but usually got 3. 

And we used to do a lot of eccentrics (before HARN/CORS) to tie in triangulation stations that were not occupiable, those were usually solars because we were close by and the accuracy requirement was a bit looser.  

Haven't done any on an actual job in probably 10 or 15 years. But I still mess around with them. 

 

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@john-hamilton

If your hosting workshop, I’d like to attend (or assist)

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John Hamilton
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@larry-scott

I would like to do one, but I have been told several times that "it is an obsolete technique, no one does them anymore". I always try to present at Trimble Dimensions, and I submitted several topics, that one they have never accepted. 

I did attend two really great "classes" at NGS Corbin about astro observations a few years ago, it was a small class and we had a good time. We were going to try and make it an annual meeting, unfortunately the class organizer (Dave Lehman) passed away suddenly. 

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John Hamilton
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In 2011 and 2012 there was an astro class at NGS Corbin. Here are link to the classes that were given...

https://www.ngs.noaa.gov/corbin/class_description/Astro_Azimuth_11.shtml

https://www.ngs.noaa.gov/corbin/class_description/Astro_12.shtml

If anyone is interested, maybe we could do one again...

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Alan Chyko
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@john-hamilton

I don't believe we covered this at all while at Penn State (97-99), but have always wanted to give it a whirl.  I would love to attend a class on this.

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Bill93
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Posted by: @alan-chyko

@john-hamilton

I don't believe we covered this at all while at Penn State (97-99), but have always wanted to give it a whirl.  I would love to attend a class on this.

I'm surprised that it wasn't at least mentioned if you took surveying courses there, since Ghilani is from Penn State, and the Wolf & Ghilani Elementary Surveying book covers azimuth by Polaris  in sufficient detail.  

I cheat and use SPADE or MICA instead of going through the equations myself.  The azimuth of Polaris given by the free program Stellarium is probably accurate enough for much work and the program is a lot of fun, too.

The advantages of Polaris are that time is fairly non-critical and you don't need a filter.  The disadvantages are that you need a right-angle eyepiece if you are above about 40 or 45 degree latitude (depends on your instrument), and have to do it outside normal working hours (twilight is best) unless you are in a place with very clear sky and have excellent instrument optics.

The problems with sun shots are the filter, the right angle eyepiece for some times of day, and very critical timing, but you can do them during normal working hours.

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Mike Marks
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When working for the BLM in 1970 I had the privilege of being a member of a Cadastral survey crew doing multi-mile traverses in thick wooded country using a solar transit (Smith Solar Attachment).  We'd take a solar shot when the sun was visible through the trees, several hundred over the course of the season.  We'd also shoot Polaris using a T-2 with a right angle eyepiece prism once a week, surprisingly (for me)  during daylight.  Later when working for a County I convinced the boss to buy a Roelofs Prism for our T-2 which we used often for the same purpose, and  for establishing orientation at sites (gravel quarries,  etc.) with only one (or no) control station.

Of course when GPS became available solar accessories were relegated to the storage room.

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