Astrometric measurements for position determination?

Some clarification of your goals might help focus the replies.

If you are talking about finding latitude and longitude from observations of stars and the sun, then older surveying books would be a good resource. Also search for some of Scott Zelenak's posts on this forum where he has written about practicing such observations. Also, Kent McMillan had a thread about trying to analyze old astronomical measurements to confirm a land grant corner.

The limiting precision is grossly large compared to GPS precision. Pretty easily 1 mile with readily available equipment, maybe tens or a hundred meters with the ultimate effort and equipment.

Atmospheric refraction is the most obvious observational problem. To overcome that you need to average many observations taken on stars in opposing directions.

Deflection of the vertical is an obstacle in relating your astronomically determined position to geodetic position. Many seconds of deflection occur at some locations, corresponding to a few hundred meters of position that need to be adjusted for. Deflection is perhaps known to a tenth second or better at some locations, which will correspond to tens of meters of position uncertainty with perfect astronomical measurements.

Complex proposal.
If you are interested in the mathematics of the proposition, they can be found in several definitive sources. The procedures vary from vectors to spherical trigonometry.

The current official vector method can be found in, "Mean and Apparent Place Computations in the New IAU System. III. Apparent, Topocentric, and Astrometric Places of Planets and Stars", and "Procedure for Computing the Apparent Places of Fundamental Stars (APFS) from 1984 Onwards". Both are freely and easily found on the web and can be quite daunting. The new system requires input from the JPL ephemeris DE200, which can also be found on the web.

As to Spherical Trigonometry, which I find more enjoyable, there are several excellent books available. Jean Meeus', "Astronomical Algorithms, second addition", is practically a cookbook. The 1998, or even better 2005 editions, are pretty error free. There is a lot more than you need, as in the other books, but they are perfect for beginners and experts. Peter Duffet-Smith wrote, "Practical Astronomy with Your Calculator" in the seventies and the third edition was published in the late eighties. He has just this year published the fourth edition, "Practical Astronomy with your Calculator or Spreadsheet". And he provides copies of his spreadsheets at the publishers website; http://www.cambridge.org/features/astronomy/default.htm . Neither of these books specifically caters to our particular needs, however, they are easy to comprehend and the learning and manipulation is the fun in it, isn't it?

I'm still driving through the IAU recommendations myself and don't think I will change to that system. With spherical trig, there is no need for outside sources (JPL DE200). I have created several spreadsheets using the books I mentioned and I can compute the azimuth and altitude for any star or planet at any time to an accuracy of several seconds - refraction excluded, of course.

And that was a great feeling of accomplishment, so I hope you take the leap and enjoy.

Two older but exceptional PDFs on the web;

Field Astronomy for the Surveyor (12 Megs).
This is a direct download, so beware unless you have a high speed connection.
http://gbennett.customer.netspace.net.au/FieldAstronomy2/Field%20AstronomyPDF.pdf

Introduction to Geodetic Astronomy (17 Megs)
This is a list of lecture notes from the University of New Brunswick, number 49 is the link.
http://gge.unb.ca/Pubs/LectureNotes.html

And if you really want to fry the noodle, try Ivan I. Muellers' Spherical and Practical Astronomy book.

These three are FK4 based, so they are dated, and the methods aren't current.
But that doesn't mean they are not useful.

> I'm wondering if some of you fine folks could direct me to a good resource(s) to learn about using astrometric measurments to determine position? I realize I can google myself to death, but why not ask the experts? 😉
>
> Thanks in advance,
>
> Jason

Welcome Jason, it's good to see our BC brothers posting...:-D

I picked up a book called Celestial Navigation Step by Step. by Warren Norville. International Marine Publishing Company Camden, Maine, for a dollar :clap: at a flea market over Labor Day Weekend.

> Warren Norville comes from a family with a seafaring tradition that dates back to the Atlantic packets and clipper ships. He has been a boatman since early childhood.

It's a good book, presented in a clear, easily understood, step by step way.

Feel free to email me with any questions and I'll see what I can do.

Doug

Thanks for the helpful resources everyone 🙂

I'm starting to dig in and there's a lot to get into here. Wish me luck!

Thanks again,

Jason