Yep, me also. We spent more time looking in the girls dorm than we did looking for Polaris.
There was a sun shot on the exam. And I didn??t skip over that question.?ÿ
I worked for a shop that did one while I was there back in 2008 or so, it was on a Forest Service project if I recall correctly. I wanted to tag along but there was other work for me to do. Beyond that I have never heard of anyone doing one post GPS era.?ÿ
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 don't believe we covered this at all while at Penn State (97-99), but have always wanted to give it a whirl.?ÿ 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?ÿ in sufficient detail.?ÿ?ÿ
I cheat and use SPADE or MICA instead of going through the equations myself.?ÿ 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.?ÿ 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.
To do an astronomic Az observation you need a geographic coordinate and good time. In say 1981 to get a geographic coordinate for a solar observation the method was to plot your location on a quad sheet and interpolate the coordinate.
This of course introduced error, then to get accurate time varies methods were used, one surveyor would listen to his radio and sync his watch to the time stamp at the beginning of each hour, or you could call the number in Colorado and sync to it.?ÿ
Of course, now there are better ways to pin down your location and your time, I see some statements of solar's within 5" which wasn't possible in the field doing real work just a few years ago.
And don’t leave out the software. Back in the day most of the time spent was in reduction.
So with lat long, precision time, quartz stop watch, defection of the prime vertical database, and software, that makes azimuths: Better Faster Cheaper. A good reason to keep the skill alive.
Really learning Solar azimuths teaches a lot.
Doing Polaris shots in daytime requires an extended sun hood. One can be made with a toilet paper core. Cut it the long way and use two with overlapping gaps for larger diameters. Flopping the scope requires removal of the hood. Flat black paint inside the hood helps. A permanent black marker is OK as the cardboard surface breaks up reflection. Set a North reference stake on an early shot so one can reacquire Polaris quickly after any observation break. It speeds up observations having a timekeeper/notekeeper.
Question, assuming astronomic tables are in real time, GPS time requires further adjustments?
Paul in PA
Doing Polaris shots in daytime requires an extended sun hood.
I tried a 11" tube made from black paper and couldn't see any difference at the time Polaris was fading away in the morning.?ÿ So the clarity of the atmosphere is also important.
Question, assuming astronomic tables are in real time, GPS time requires further adjustments?
You hardly ever see GPS time displayed.?ÿ Most devices will convert it to UTC for display (using the leap second count).?ÿ Precise astro work requires UT1 (that takes into account more subtle effects), which is within 1 second or less of UTC.
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You almost never see a true gps time except in a rinex file. Receivers display UTC.
For sun shots, UTC needs to be amended to UT1. That correction +/- few tenths, can be found online, Bulletin A. The current DUT correction:
“DUT1= (UT1-UTC) transmitted with time signals = -0.2 seconds beginning 02 May 2019 at 0000 UTC”
https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html
A guy who posts here once in a while wrote a program for your HP calculators that we used as DC's way back when. He would update them yearly with a new ephemeris and all that was needed was to push the enter button when you were on the leading and trailing edges. The program would then calculate the AZ, of course it worked best when you did multiple observations. It was quick and accurate. Big improvement over the hand calculations.
Although, after some years we stopped using the HP calculators and if I wanted to do a Solar I had to sit down and hand calculate them. Kinda going backwards.
It really is something all surveyors should know and do at least once, but I'm probably never going to do another one, been there, done that.
I was brought up around solar observations. Dad wrote a basic program back in the 80's to reduce them. We hand entered the programs in our HP calculators from the back of the Elgin, Knowles, and Senne books in the 90's. Later we had a TDS data collector that would reduce them and directly read the angle from the instrument and time from the internal clock making them very fast to acquire.
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In my opinion it is a tragedy that celestial observations have not been fully embraced by surveyors everywhere. All of our surveys refer to "North" but few seem to know how to determine North and what it actually is if they did (geodetic, astronomic, grid, etc.)! So most references to "North" are vague at best. Even today, with GNSS being ubiquitous, many surveyors don't seem to understand North given their metadata statements.
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I don't know why celestial observations are not even more widespread today than they were in previous generations. Technology is available right now that should allow celestial observations to be acquired and reduced with high accuracy in seconds. GPS provides time and position and accurate engines can be installed on instruments and collectors. Robotics can track objects in bitonal images, making even then act of sighting automatic.
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I realize I'm a salesman for Javad, as my profile indicates, but I'll offer that the J-Mate (currently in beta-development) is designed to automatically find the Sun, make observations, and reduce the observations in seconds, with virtually no input from the user. The hard work once required to get accurate directions can be eliminated with current technology, but it seems few ever realized the significance of them.
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E&K AstroROM module for the 41 is available for i41CX+.
I shoot the sun regularly for kicks. I wrote a comprehensive spreadsheet. Reduction made easy. I have a little GPS receiver with a pps strobe for UTC time. It’s easy peasy and incorporating Xi Eta it’s a whole lot better than before. Obs still take close to an hour, but reduction is 25-20 minutes.
However, I guess it’s mostly nostalgic
This site may be of interest to those seeking ephemeris information.?ÿ I haven't tried it myself.
Surveying in the 1970's and 80's i would do a Sun shot on every survey. Sometimes 2 or 3 a day. Even had a Sunshot calc on my PLS test. I tried to teach others how to shoot the Sun and Polaris but they never got the hang of it. I still shoot Polaris?ÿ sometimes just for fun.?ÿ
