Magnetic declination is an chief principle to accept when navigating your road buttoned up the wilds with map and compass.
Yet its a tricky affair to bethink, at least the road it has traditionally been taught, using an addition / subtraction adaption. Aloof when you anticipate youve grasped it, the abstraction floats away, according to fog in the morning ablaze.
Able-bodied there is a child’s play, practical access to adjusting for magnetic declination when finding your bearings. The entire explanation begins with a definition of north.
There are 2 Norths
A lot of bodies apperceive that there are 2 norths in terms of maps and compasses. A map shows accurate north, or the Geographic North Pole where a
ll lines of longitude accommodated. The earth rotates around an imaginary axis that runs buttoned up the North and South Poles.
A compass darner points to magnetic north, which is curved by the earths magnetic field. The location of magnetic north moves over age, at about 5 miles per hour. Adapted any more it is slowly creeping around somewhere NW of Hudsons Bay in Canada, about 450 miles away from accurate north.
The angular aberration between accurate north and magnetic north is accepted as declination, or variation in the aviation apple. Declination is altered for altered parts of the globe. In Washington State, the angle of declination is 20°east. This means that magnetic north is 20° east of accurate north. In Tennessee the angle of declination is 0°, and in Maine, its 20° west.
Declination values can be activate in the margins or legend on topographic maps. As the point of magnetic north is constantly moving, it is big to accept a recent topo map for finding your road in the woods.
A agnate point to bethink is that compasses are calibrated for altered parts of the apple. So when you purchase a compass, be sure that it is intended to be used in the area of your ample hiking vacations.
How to Acquisition Your Bearing
Chase these steps to acquisition your bearing:
1. Abode the compass on the map with the arrow on the base plate pointing in the direction you appetite to action.
2. Turn the dial face of the compass so that north on the compass is analogue with north on the map.
3. Abode your compass akin in the palm of your hand and turn yourself until the darner in the compass aligns with the North marking on the face dial.
4. The ample arrow on the base plate is any more aligned with your bearing.
Declination Amount and Bearings – A Trick to Accomplish it Stick
If you walked 10 miles buttoned up the woods in Washington State, without factoring declination amount in your bearings, you would finish over 3 miles off target. Thats too much!
To avoid confusion in finding bearings, accumulate the central principle in apperception:
Accomplish map bearing = magnetic bearing.
You will accomplish this in the field by adjusting your bearings to compensate for magnetic declination. There are 2 ways to statement for magnetic declination in finding your bearings: an adjustable compass and marking your non-adjustable compass.
The easiest road is with an adjustable compass. Simply turn the declination adaption screw on the compass to the correct amount and all readings are automatically converted to accurate north. If its available, its always ace to accept an adjustable compass on your airing.
The abutting ace road to statement for declination is to mark the declination amount on your non-adjustable compass at the alpha of your adventure.
Thats child’s play to accomplish. For archetype, when the map indicates a declination amount of 20° west, you will mark your compass dial at 340°. If the map indicates a declination amount of 10° east, you will mark your compass at 10°. Accomplish the mark with a permanent marker and erase subsequent with rubbing alcohol.
Any more when you booty your bearings in the field, abode your compass akin in the palm of your hand and turn yourself until the darner in the compass aligns with the declination marking on the face dial. Then the ample arrow on the base plate will point toward your bearing and automatically compensate for magnetic declination.
Originall posted December 15, 2012