Solar Observations

> For those of you who do solar observations, do you do them in the mornings and afternoons when the sun is close to the horizon? If not, do you have to use an eyepiece diagonal to see the sun near noon. I work just south of 30 degrees latitude and the sun at times can get to almost straight overhead.

My practice is to do the observations when I can catch the sun at about 75°. This usually is early or later in the day. I have a diagonal eye piece for my instrument but prefer that it never sees the light of day.

Did a boat load of them in the early days of working in the telecom end of the business. Had to give them "North" on the ground so they could orient their equipment. Or they wanted bearings on the legs of the water tanks or bearings on the exterior roof walls. Best times were early a.m. when sun was rising. Always used trailing edge observations. Didn't want to be at site at sunset because then the boss would have to pay us overtime. Had a HP 48GX with elgin knowles astro rom card in it speciffically for sun shots. After awile could have values in less than 15 minutes with some up front preperations. Biggest problem we had was trying to convince the owners of the buildings that we needed access early a.m. on the roof on a sunny day.

Haven't done one in awile now that the equipment is pointed generally in the direction and electronically tuned to max.

I had/have all the accessories, right angle eyepiece and solar filter. But as the total stations changed so did the accessories. Meaning the eyepiece and filter for one of my Topocons wouldn't fit the newer one. Plus they ran about $750 apiece.

Started in business in '85 and used them on most every job till getting GPS in 2000
and am still amazed at how close some of my old jobs tie in with the GPS. There are one or two others in the area that have used them. I think a reproduceable bearing system is one of the best things we could pass on to future surveyors.

> I have noticed a few posts concerning people doing solar observations for azimuth determinations. How prevalent is this nowadays? I thought with the advent of GPS that solar (or other celestial) observations were pretty much obsolete. I did a 2 night Polaris observation for azimuth once for my senior project in college (in the late 1990's). Since then, I have never heard of anyone around my area doing one.
>

Dad began doing Solar observations in the mid eighties until about 2001, when we invested in survey grade GPS (post processed). Then in about '04 we started getting work that required knowing a good bearing at the beginning of the project instead of the next day after post processing. This work lasted for about five years, so I did observations about once a week on average. Even with post processed GPS, sometimes a quick solar at the beginning of the day can be a big help, or a solar half way along a long traverse for a quick and dirty angular check is helpful. With RTK, it's perhaps less important now. The main argument for astronomic observations in the context of the past few days' discussions is that they still produce incredibly retraceable bearings and don't require a significant investment in equipment. For less than $500 a person could be very well equipped to do them without buying (comparatively more) expensive survey grade GPS equipment, and could provide a better product for their clients, future surveyors and for themselves.

:good:

Bow Tie,

There was a time when solars were almost a common every day occurance for me. To each his own on methods, with practice they all work well.

Try to keep your observations aprox. 2 hrs. after sunrise or 2 hrs. before sunset to minimize refraction and parallax.

My best results were with a T-2 Wild theodolite with a Roleof Solar Prism where I could shoot the center of the sun and quit screwing around with trailing and leading edges etc.

With a Shortwave radio tuned to 5.00MHZ you could take the shot on the tone with 3 direct and 3 reverse positions.

With a HP program you could check your results in less than 5 minutes and be gone...

Each year I would hold a contest for my party chiefs on a known NGS geodetic azimuth line and have them use what ever method they wanted for solar observations. The one closest to the true azimuth would win a $100 gift of their choosing. Most azimuth returns were within 3".

Back in the early 80's, there were six of us in a group taking solars for the U.S. Mineral Surveyor exam and we all assisted each in taking our required solar observation and azimuth determinations. There was a plethora of methods employed, fortunately I knew my methods were nearly the same as a good Polaris observation session. All our comparisions of azimuth were within 10" of each other. The mineral surveyor was required to be within 1' of true azimuth. With much jubilation and the depletion of brewskies from the nearest local liquor store, we celebrated the successful completion of that part of the exam.

B-)
Pablo

> For those of you who do solar observations, do you do them in the mornings and afternoons when the sun is close to the horizon? If not, do you have to use an eyepiece diagonal to see the sun near noon.

As the altitude of any target, including Polaris and the Sun, increases, the accuracy of a horizontal angle measured to it with a total station or theodolite decreases. This is a function of the geometry of the situation and how small errors in levelment are magnified at higher altitude angles.

The ideal altitude for observing the Sun in my experience is between about 20 and 25 degrees. If the Sun is too low, its edge or limb starts to become indistinct. Afternoon observations are better in Texas because there are less likely to be clouds to contend with during the observation, which should be done as one more or less continuous operation instead of waiting for minutes for clouds to come and go.

:good: :good: :good: T-2 Wild theodolite with a Roleof Solar Prism

Cool! You actually had to think about what you were doing back then! Now the coordinate cowboys just hop out of the truck and start shootin'

I may be on the younger side, but I still like to think I am old school in a lot of ways. While I have never had to use astronomic observations in the field for a job, I did solve the problem on the test!

FROM ONE YOUNG SURVEYOR to another, check it out. astrometrics are well worth the pursuit. see you at corbin virginia next november for the astro training?

I agree except don't point a total station at the sun without an objective solar filter.

It is useful to be able to do astro observations.

I haven't done a sun shot lately, but I've had a few jobs where I would have liked to have done one. My problem is I don't have a solar fiter for my Topcon and I can't bring myself to pay the $307 for a new one. I've only seen one on Ebay and someone beat me to it.

Pablo

I just looked at my FIRST appointment as a U.S. Mineral Surveyor.

It was dated Fedruary 19, 1981.

Your post really brought back memories of the Examination (and Solar Observation) in Reno. As I recall, I did mine with a T-16.

Were you in that group?

Loyal

That is why I have switched to Polaris when I need to do a celestial observation, no filter needed, not as convenient though!

SHG

Some have found it during the day but I haven't been able to do it until close to sunset. Maybe it takes better optics than I have available.

Dave...

More likely your problem is the SMOG in the land of fruits and nuts!

Come up to God's country, where the skies are clear, and the stars are bright.

B-)
Loyal

Dave...

That could be but the air is pretty clear and cold right now. We have had some cold fronts move through. I tried yesterday. It seems to me I was able to do it once with the sun still well clear of the horizon in the late afternoon but not at mid day.

Dave...

>It seems to me I was able to do it once with the sun still well clear of the horizon in the late afternoon but not at mid day.

At around 30deg North latitude, Polaris looked like a dusty spark of a star the few times I observed it and that was at night. I think the Polaris observations during the day are more of a high altitude and/or higher latitude thing.

Dave...

Kent-
I'm 8 and a half degrees north of you so I think the star is that much higher in the sky here (if I am remembering right).

-Dave