Re: Navigaion -determining position with ref. to the Sun/Moon
I fly with the GPS in true as the variations in my part of the world are greater than 60 degrees. As there are few ground features (infact often completely absent) as a gross error check on the GPS, I do the following on the back of the flight log.
First, the sun moves 360 degrees in 23 hours 56 minutes and 4 seconds. That's 15.04 deg/hr.
Now I am lon E078 in the southern hemisphere, it's 0430 UTC, what brg is the sun? There are two stages to work this out. First is to work out where the sun is now w.r.t. an observer in my hemisphere at 0deg lon.
At 0 deg lon 0000 UTC the sun should be due south (southern hemisphere) (180T). So now at 0 long it should be 4.5*15.04deg/hr east of south = brg 112T.
The second part of the calculation is to correct for my longitude. That is to work out what fraction of 24 hours I am ahead or behind the observer at Greenwich. I am Lon East, so I am ahead. 78/360*24=5.2 hours.
5.2 hours @15.04deg/hr= 78 degrees.
The sun should be 78 degrees east of the previously calculated point as I am to the east.
So the sun is BRG 034True at this point in time.
There are other formula to work it out, but as I am hopeless at remembering them, I calculate it practically by thinking out the above, and there are a couple of different ways to do the above. Remember to convert the times/direction for your hemisphere, then add on your local variation.