Q:
Sean,
Question about declination
If "solar declination" is discussed then this is angle between magnetic south and true south? If east of 0° (in US ~ Mississippi River) then you add the declination angle and if west of 0° , then you subtract the declination angle?
If "declination" is discussed then this is the opposite of solar declination (magnetic north compared to true north)? If east of 0° (in US ~ Mississippi River) then you subtract the declination angle and if west of 0° , then you add the declination angle?
thanks,
A:
If you are converting from magnetic azimuth to true azimuth, you will add to your magnetic azimuth in the west (about west of the Mississippi) and you will subtract from magnetic declination on the east coast.
One way people remember this is by saying east is least (you subtract in the east).
If you were going from true to magnetic, you will do the opposite.
Another way of looking at it is you will rotate clockwise to make the correction on the east coast and you rotate counter clockwise on the west coast to make the correction.
If you sit there and think about it, you can contemplate how the magnetic north pole is over the middle of Canada.
Most of the time, you do not have to worry about magnetic declination, because all of our GPS, satellite and maps are already at true azimuth. If you use a magnetic compass, you will have to correct for magnetic declination.
If you fly an airplane, then you will have to get really good at converting back and forth from magnetic and true azimuth. Runway numbers are based on magnetic azimuth.
Thanks,
Sean White