Celestial Nav Question

[Billofthenorth]

Howdy folks, I am new to celestial navigation and to this forum, I have a quick question that I hope someone can answer.

One of the things I am learning is navigation with the Bagnold sun compass, this requires setting an azimuth to the sun every 30 minutes or so at the users approx lat/ long. This information used to be contained in the Davis tables of sun's true bearings and azimuths, as far as I know this is no longer in print and all I can find online are photo copies of 50 or 60 year old books.

Does anyone know if there is a modern equivalent to Davis, might this information be contained someplace in the nautical almanac?

TIA

[gjordan]

Wow, I have done a lot of celestial , and never heard of this method. I have been waiting for someone that is familiar with it to chime in, but no one has. Is this based on a book, or something that we can look up???? _____Grant.

[Jim Cate]

This is going back a long ways, but some years ago "Lee Helm", a frequent character in the "Max Ebb" section of Latitude 38 published a neat little program for determining the sun's azimuth. Written in Basic and only a few dozen lines of code... input Lat/Lon and time, output current azimuth. I had it programmed into my old Toshiba pre-laptop, but code and computer are long gone. Her application was for compass correction, but it might well do for your situation.

Now, how to get a copy? Beats me! Lat does have archives, but possibly not going back that far... this was in the late 70's or early 80's, while I was still a worker bee. Some internet research might well dig it, or an equivalent code out of cyberspace.

Good luck... and I too wonder about your Bagnold sun compass technique.

Cheers,

Jim

[banjoship]

I am not familiar with the method you mention.

You may care to ask your question at the NavList forum
fer3.com: NavList celestial navigation community

This is a forum concerned with traditional navigation methods, and has some very knowledgeable members. Possibly the best repository of knowledge on the subject available.

Lee

[Billofthenorth]

These should help with the context, just part of my effort to gain more information on the subject.

The sun compass is generally used (or was) for land navigation in deserts but the knowledge base is more or less the same as one would have used at sea.

These guys would go out exploring and surveying using the sun compass as a very accurate method of running navigation then fix their positions at night using the traditional methods with sextants / theodolite.

I've included a link to an excellent book on the sun compass, hope that doesn't break any rules, I'm not selling it.

Ralph Alger Bagnold - Wikipedia, the free encyclopedia

desertstories.org | The Bagnold Sun Compass

https://www.google.com/search?q=bagn...w=1280&bih=620

[Billofthenorth]

Originally Posted by Jim Cate

Good luck... and I too wonder about your Bagnold sun compass technique.

Cheers,

Jim

Imagine a style or gnomon centered on a reversed compass dial which rotates. You would take the value on the dial for the azimuth of the sun for your approximate lat/long and rotate the dial so that it is at the lubber line at the bottom of the dial (taking into account the equation of time) another rotating dial has a directional arrow which you position at the value for the true course heading you want to travel. You then position the entire vehicle so that the suns's shadow is over the direction arrow and you are now headed in that direction. That's a simplified version of how it works. Apparently these guys found it accurate to within 1% or so back in the 20s and 30s.



I guess my other reply has to be approved by a moderator, it has some links that may help those interested in this form of navigating to follow up. Seems rather simple as long as one has a reliable source for obtaining the azimuth of the sun.

I'd heard of the sun compass for years but it's only been rather recently that the extent and accuracy of it for primary navigation became known to me.

[StuM]

How accurate do you need he azimuth of the sun?

A program to calculate to within about 1 degree based on Lat/Long and time is quite simple. If you need to get down to fractions of a degree it gets more difficult.

[Billofthenorth]

Originally Posted by StuM

How accurate do you need he azimuth of the sun?

A program to calculate to within about 1 degree based on Lat/Long and time is quite simple. If you need to get down to fractions of a degree it gets more difficult.

They would round up or down to the closest degree so I think 1 degree would be acceptable, come to think of it I think they also interpolated between degrees of latitude (to save on carrying the entire Davis tables) so I imagine that would be acceptable.

[Jim Cate]

Bill, thanks for the explanation. I thought when you were saying it was a means of navigation that you meant deriving one's position, not just finding a true direction.

Cheers,

Jim

[StuM]

Ok, here's a first pass at a very simple Windows application to give Azimuth,Elevation, Sunrise,Sunset etc for a specific Lat/Long and date/time.

It also produces a full list of Azimuth/Elevation at 1/2 hour intervals for the day in question

Just download, and run the .exe which is in the zip file. (It's only a 45Kb download)

http://www.camcopng.com/download/SunAngle.zip

I will possibly create an Android version over the weekend, so if you have any suggestions, please PM me.

[Billofthenorth]

Thanks, it seems to do the trick.