TRUE NORTH QUERY

[n4si]

> I hate to bring this up [but does] anyone know a quick and dirty
> way of locating true North? Can it be as simple as adding an x
> number of degrees one way or the other to a compass north reading?
> 
> What say you? Mick...W4YV
> 

Is it ever! There is a factor called variation that represents the
difference between true north and magnetic north in any given
location. All aviation charts (I'm a pilot and air traffic
controller so don't you guys nitpick me about RF charts) have
isogonic lines (lines of equal variation) printed on them (for those
who can't stand not to know everything, the line of 0 variation is
called the agonic line).

Simply take the variation (expressed as degrees East or West) and 
subtract or add to the compass bearing to get True North. 

Which do you do? In aviation we say "East is least and West is
best." If you are in an area of 4 degrees West variation, add 4
degrees to your compass heading (in your case, 0 or North) to get the
true bearing. That means that if your compass is pointing to the N,
you are really pointed at 004. Thus, turn left 4 degrees (so that
your compass reads 356) and you will be pointed to True North.

Call the FBO (fixed base operator) at your local airport and ask the 
variation in your area. 

(From the "more than I thought I wanted to know" department: do not
confuse variation with deviation. Deviation is the factor derived
from the magnetic effects of the vehicle on the compass installed in
it. In aircraft, there is a deviation card next to the compass. No
trip can be completely flight planned without access to that
information. 
     True Course +- variation = 
          Magnetic Course +- deviation = 
               Magnetic Heading) 

Has anyone mentioned the North Star? It's at the tail end of the 
Little Dipper (which is hard to see), but it's "pointed to" by the 
ends of the "bucket" of the Big Dipper (which is easy to see). Note 
that this must be accomplished with clear skies AND at night!

For the flamers with pens poised, I live practically on the agonic 
line, I haven't had to correct for variation in 30 years. As a 
controller, you issue a heading and the airplane flies it. If it 
looks good on the 'scope, it was the right heading. Variation doesn't 
come into play.

One final thought. HF antennas typically have half-power beam widths 
of 60-75 degrees. Except in the western U.S. where variation is in 
double digits, correcting for variation isn't all that important. 
VHF/UHF? That's another story; some of those beamwidths are pretty 
tight.

73, Rod N4SI
    The DXer formerly known as N9AKE
         (c) 5 November, 1996

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