Science · 6 pages · 12 min
How magnetic declination shifts a map bearing
Declination is the angle between compass north and true north, and it shifts a bearing.
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From the opening
Magnetic declination is the angle, at a given place and date, between the direction a compass points and the direction of geographic north. A bearing taken from the map's meridian and a bearing taken from the needle differ by that angle, so one must be shifted to match the other. The opening covers the angle between two norths, why the shift carries a sign, and why one correction does not travel.
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Inside
- The angle between two norths
- Why the shift carries a sign
- Why one correction does not travel
- What isogonic charts record
- Where the idea stops applying
- A distinction worth keeping
Sources
- Magnetic declination, or variation
- Halley's chart of magnetic variation