declination= "...is that in which the primary circle is the celestial
equator, the secondaries to which are the hour circles. The norigin is that
point of intersection of the celestial equator and the observer's celestial
meridian which is above the horizon. The hour angle indicates in which hour
circle the point to be defined is found, and declination gives the position
of the point in that circle measured from the celestial equator." from
Technical Manual, Celestial Air Navigation, TM 1-206, War Department, 2 May
1941.
Variation= "a. Definition.-The magnetic compass needle if operating
perfectly and undisturbed by outside forces will point to the magnetu=ic
north pole. The earth's magnetic poles, with the magnetic field which
controls the compass, are not located at the geographic poles of the earth.
The magnetic pole in the Northern Hemisphere is at approximately latitude
71 degrees North and longitude 96 degrees West, while the southern pole is
at latitude 73 degrees South and longitude 156 degrees East. Variation
(Var.) is the angle between the plane of the true meridian and a line
passing thru (sic) a freely suspended compass needle which is influenced
solely by the earth's magnetism. It is named east or west according to the
direction of the compass needle from true north. Variation changes with time
and place." Technical Manual, Air Navigation, TM 1-205, War Department 25
November 1940.
and ibid at page 45
"Magnetic deviation.- Definition.- Another reason why the compass fails to
indicate correct magnetic direction is due to magnetic deviation...The
indication of any (magnetic) compass installed in an aircraft will be in
error an angular amount equal to the number of degrees that the earth's
lines of magnetic force are deflected from their normal path by the magnetic
properties of the airplane. This error is known as deviation..."
The laws of mathematics and physics haven't changed...one hopes
Stu Greene WA2MOE
7537 North 28th Avenue
Phoenix, Arizona 85051 USA
wa2moe@doitnow.com
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