California Surveyors Forums

I need some help! I have not calculated a sun shot or star shot in at least 40 years and I have a reason to do that now. I am establishing a meridian in my back yard and have to believe that there are computer programs that are available to help me?

Forty years ago, I did not have the computer technology like I have now!

Keith

SMI will do the calcs for a sun shot with just the Standard cogo card in a 48
I think Starnet will also do what you want on a PC.

Thanks Stephen,

I guess this won't be that easy...I don't have a 48!

Thanks Michael,

Looks like I have some relearning to do!!

Thanks Woodcutter,

Woodworker here.

Just a reminder to use a proper lens filter when observing the sun so you don't fry your eyes and/or instrument internals.

Good idea Mark and I have a dark lens cover for the transit.

I haven't done one in 25 years, and at that time I couldn't find anyone who had done one for a real, actual non-school project in over 15 years.

When I later worked in AK, I learned that the BLM was still using them when surveying remote native allotments. That was in the mid/late 80s. I'd bet that they've been using GPS exclusively for establishing bearings on such surveys for the past 15 or 20 years.

If you PM me and send me the following: Method (Leading edge/Trailing edge/Center), dat of obs, approx Lat and Long (can be scaled from Quad sheet) and the obs data, (time of each obs, angle to BS and Horz angle to the sun).

I will calc and send you the results. It only takes a few mins.

Observation times are critical when using the Hour-angle method. For best results, use the WWV broadcast UTC times to set your stopwatch to. And be sure to note the precise time corrections, in tenths of a second, that should be applied. This time of year, solar obs are easier early in the morning before the sun gets too high.

With practice, very good results are possible.

RAM,

Will you do that with a Polaris observation too?

Keith

Laplace correction.

Keith-

I did that very thing. My baseline is in the front yard as free from local attraction as I can get (mostly power lines in the backyard and parked vehicles in the front yard).

I used Polaris which is really simple to observe. You can easily see it with the Transit at about sunset or maybe a little before. There is still plenty of ambient light at sunset for sighting a target and taking notes. You need to know where it is to find it, though. One way to use the compass to mark a north point then turn a calculated angle to Polaris plus a calculated vertical angle. Then focus in and out until you see it. Or wait until dark, see the star, turn the angle to north and mark the spot. Wait until sunset the next day (or get up early) and then turn to the star. Or you can start while still dark (early morning) and wait for enough daylight to see what you are doing. Since you are doing this at home it is convenient enough to do over a day or two. Be aware, though, all of your neighbors will want to know what's up. You are trying to get finished before dark and that is when they all show up to pepper you with questions.

There is no need for special equipment or highly precise time. I think the clock on your cell phone is good enough. I use my satellite adjusted alarm clock for the time to the nearest second.

I have a spreadsheet which reduces the observations but it's kind of manual. It isn't software but works for me. You are welcome to a copy. You have to hand enter the ephemeris data and your angles. Then you need to possibly edit the formulas so the angles mean correctly (it isn't automatic). It's not a big deal if you know how to use Excel.

Jerry Wahl has both the solar and polaris ephemeris in the same place at cadastral.com.

-Dave Karoly
karolysurveyor@gmail.com

Keith, I will have to check my software on Monday, I am not sure, however I have had the occasion to do solar over the last few years, it is a handy tool, to some, Old school, but try using GPS at the bottom of an East-West canyon, it is good to use all the tools in the box.

Never done one and missed that week in school too - how bad is that.


Don't know if it's changed or not, probably not, but in the 1980's the feds still required a sun or star shot for mining claim survey BofB.

The calculations for Polaris are simpler than the sun, too.

Parallax and refraction are not an issue.

You don't need to figure in the semi-diameter of the sun (unless you have a Roeloffs prism).

But now you have me interested. Maybe I will try a sun shot with my Dietzgen 6100 series transit. I don't have good enough time but what the heck, it isn't real. It would be a way to see how close I can get to the bearing I got for my baseline from Polaris.

It's kind of tough in June, though with the sun so high in the sky.

You have to get up early or stay out late and have clean air. Time is easy, you can set your watch online or by calling one of the atomic clocks, check your watch again when you are done, and apply a correction.

I can see Polaris by 8:30pm right now in Sacramento but I see what you mean, being a Surveyor my bedtime is 9pm ;-).

In Sacramento it is about 39 degrees above the horizon. In Southern California it would be a little lower which make the observation a little easier.

In December I can see it probably at 4pm assuming the weather is clear.

edit-now Keith has me interested. I will try an hour angle solar with my Dietzgen 1' transit (I don't have a solar filter for my Topcon TS). I have Wolf & Brinker Elementary Surveying 9th edition for how to to calculate it. I also have a 1940 edition of Davis and Foote I will look in to see what they say about it.

My plan is to project the image onto a white card which is understood to be inverted. I will turn angles to the trailing edge of the sun (right side of the sun on the card).

It's my understanding that the vertical angle (not zenith) to Polaris is equal to the latitude of the location of the observation. I've done observations on Polaris when I was near 42 N, but I don't recall checking the vertical angle to see how closely it matched my latitude.

Time to dust off the ol' total station and take a look-see!

The altitude of the pole is equal to your latitude.

Polaris is somewhere within 1° of that.

this is cool, I think everyone that goes out and practices a solar obs should get/claim CE's. Dont forget if doing a sunshot, without a filter, do not use a total station, it can fry the diaode, when using a conventional instrument, you can use the white paper metheod, takes a little longer but does work. We have a T-16 that has a right-angle adapter for reading the plates, works well. Sometimes old school is the best way to approach the problem.

I find it helpful to calculate the vertical angle to Polaris so I can get within a minute or two of it. It can be hard to find in late afternoon if it is near the edge of the field of view.

An interesting question I have is:

I find Polaris consistently about a minute below the cross hairs from my calculated vertical angle. This seems backwards to me. I thought refraction would make the star seem higher and parallax should not be a significant factor.

I observed 4 sets to Polaris last week to my baseline in front of my house using my 5 second Topcon GPT3005LW. One set appeared to be bad so I used the 3 good ones and got an astronomic bearing of N 89-40-53 E.

This evening I did 4 sets to the Sun using my Dietzgen 6100 series 1' transit. I backsighted zero on my baseline in the direct face on the first set then did 8 observations to the sun D-R-D-R-D-R-D-R then observed the backsight at 180-00. This time the second set appeared to be bad so I tossed it. The mean of the 3 remaining is N 89-40-53 E.

Not too bad for a novice who is self-taught.

I project the image of the Sun onto a card and watched the Sun's trailing limb touch the vertical cross hair and looked at the time (on my alarm clock which sets itself to WWV). It's a little bit of a matter of opinion what instant it touches because the cross hair is only visible in the Sun's disk on the card. It occurred to me when I was done that I could dial in an even minute and let that be the angle but maybe it wouldn't make much difference.

I used the hour angle method. The residuals of the 3 sets used are 25", 14" & 11". The set tossed is 15'14" which is an obvious outlier.

The residuals of the 3 Polaris observations used are 2", 1" and 1". The set tossed has a residual of 6".

Kieth,

my program will only do Solar, but still willing

Keith,
I also have a program for solar, but not for starshots.

Check out this Naval Observatory site:
aa.usno.navy.mil/software/

They claim software for positional astronomy

I also found something here.

http://docs.autodesk.com/CIV3D/2013/ENU ... Gd30e78592

http://www.cadastral.com/2012ephs.htm