I'm trying to understand the steps one would use to orient, in terms of directions, a traverse to grid north, by means of a Polaris sight. Have I got a correct set of steps?
1. Set up theodolite on a monument, A, with another monument, B, visible. Using recreation-grade GPS, note latitude and longitude of monument.
2. Sight Polaris and note the UTC time. Find angle to B. Repeat as many times as desired, keeping track of all times.
3. Convert UTC to UT1 with published values of DUT1 (or by counting the double-clicks of WWV) for each
4. Enter observation times and recreation-grade latitude and longitude into a computer program such as MICA, and receive topocentric azimuths and altitudes of Polaris. This would be geodetic azimuths and altitudes.
5. Apply Laplace correction to each azimuth to convert from local plumb line to geodetic. (This step may be negligible, depending on local gravity.)
6. Compute each geodetic azimuth of line AB and take mean of results.
7. Use recreation grade latitude and longitude, mean geodetic azimuth of line AB, and distance AB, and software from National Geodetic Survey, to compute grid azimuth of AB (assuming the length of AB is small enough that the arc-to-chord correction is negligible).
That is basically it, although normal practice is to turn the angle from the BS to Polaris. Also do D/R sets,so B(D)-F(D)-F(R)-B(R) to complete one set, do several sets and then compare the reduced sets to each other and mean them if all looks good. Your software will likely handle the reduction and meaning automatically.
Hardest part can be getting Polaris in the scope the first time, after that you know about what H/V angles should be and it is easier.
SHG
At first glance, I think you've basically got it.
Time isn't very critical on Polaris (as opposed to solar shots), and particularly noncritical if you can time your observations near east or west elongation. Your software may or may not deal with the UT1 correction, and UTC may be close enough.
You have three variables to work with in finding the right star: azimuth, elevation or zenith angle, and focus. Focus is critical because without it you can't see the star, so start by focusing on the most distant thing you can find. It helps immensely if you can start with an azimuth good enough to put Polaris within the field of view (maybe two rec GPS readings on points the bigger part of a mile apart?). Add about a minute of elevation angle for refraction.
People with clear air at high altitudes can see Polaris in the daytime. I can see it for up to an hour after sunrise and an hour before sunset. Using a black tube for a lens shade did not noticeably help me. The optimum time of day for me has been between the time I can first find it until too dark to see the crosshairs, or between morning twilight until I lose it.
To work when it is darker, make sure you have a good means of illuminating the crosshairs. I have an instrument with no illumination capability and I've found that there is some sort of parallax (10 to 20 seconds) if I put a small light in front of part of the objective lens. I need to rig up some LEDs symmetrically placed inside a lens shade.
What you observe is astronomic azimuth. It depends on your software whether it deals with the Laplace correction to get to geodetic. No reason you can't reverse 5 and 6 for simplification.
Do multiple sets of D & R to minimize the error due to any tilting of the instrument, and re-level between sets.
Polaris is a piece of cake.
Do it around dusk. A backsight natural to the west against the dusky western sky is easy to see. I used a TV antenna 500' away from my backyard.
Polaris is best at mid latitudes, it gets lower the further south you go and possibly too high in Alaska.
First I want to say that I agree with Bill (I usually do).
Many instruments have internal illumination of the crosshairs. Yours may have it, but you don't know it because you have not investigated it. If you have a Wild T-2 or T-3 you probably know that there is a kit for illumination. Later models from the same company have internal illumination built in. No parallax problem. But not well known. Who does star shots today?
If you are doing this for the first time Bill's advice to use the east or west elongation for your sight is very good advice indeed. It reduces the importance of precise timing and renders the observation much more easily taken.
On a boring historic note, my first survey crew experience after graduation from college forty or so years ago was on a crew whose party chief was a licensed surveyor.
Luckily for me has was at the top of his profession (how many of you worked on a crew with a licensed party chief) and he could afford the only electronic watch of the day- a Bulova Accutron, several hundred bucks back then. Of course he also drove a Corvette.
He drove all of us pretty hard also. My first day with him was fourteen hours. But I learned a lot from him and the Bulova Accutron and a shortwave radio got us through all of those star shots. Thanks, Dave.
