A method of navigating by the sun developed by Maj. (later Brigadier) R.A. Bagnold in the 1920s.
The most accurate way of using this device is to pre-calculate the azimuth of the sun at 15, 30 or 60 minute increments for the approximate latitude an…
A method of navigating by the sun developed by Maj. (later Brigadier) R.A. Bagnold in the 1920s.
The most accurate way of using this device is to pre-calculate the azimuth of the sun at 15, 30 or 60 minute increments for the approximate latitude and longitude where you will be operating. This gives you a true course heading. Since most people won't have navigation tables and can't do that in an emergency, I demonstrate another method using the magnetic azimuth of the sun, this produces a magnetic bearing. The equation of time was about -11 minutes on the day I did my montage and didn't appear to affect the result measurably.
The Sun's "motion" averages 15 degrees an hour but HOUR TO HOUR the sun's azimuth can vary SIGNIFICANTLY! The Nautical Almanac accounts for these differences in the GHA tables. Obtain an azimuth, check it again in 15 minutes and you can then calculate an approximate rate for the next couple of hours saving you multiple stops. Errors are often 'averaged out' over the course of a day. In any case one must travel approximately 60 miles to be one mile off course for each degree of error.
The blue model compass I used here has an extra plate (or disc) for the sun's azimuth. Since I thought it would be confusing I eliminated it as a separate part from the discussion - However for informational purposes - the degree graduations on the disc starts at Zero degrees in the same place the shadow disc reads zero or 360 (the two discs appear to be a single piece on the original device) the graduations proceed sequentially around BOTH sides of the plate stopping at 180 degrees. Bagnold mentioned that the apparent motion of the sun describes a near perfect arc though out the day. At local noon, the sun's azimuth is 180 degrees and in the exact middle of that arc. If you know where the sun's azimuth was on one side of that arc at a given amount of time before local noon, it will be in the same spot but on the opposite side of the arc the same amount of time after local noon - See why I left that bit out of the video. I suspect there are other functions for that disc that are not well known and in any case they don't appear germane to our purposes here. From my tests, I believe the compass can function accurately without using it. Of course a video cannot be comprehensive concerning a technical subject such as this. If you are interested in the sun compass functions or using it for navigation I urge you to further explore its uses and employment.
Footage of Bagnold in the field: https://www.youtube.com/watch?v=K1HHMrp07tE&list=PLswZVUdKWswbx3K7p0muZf-UyFRGOw0bB&index=2&t=27
I downloaded a printout from which the compass was made. The website is no longer active but I will give credit to the original creator should they be identified.
