Definition
The angular difference between true north (the geographic North Pole) and magnetic north (where a compass needle points) at a given location on the Earth's surface. Magnetic variation is expressed in degrees east or west and changes depending on geographic location. It must be applied when converting between true and magnetic headings or courses.
Plain English
The compass does not point to the actual top of the Earth. It points to a slightly different spot called magnetic north. Magnetic variation is the gap, in degrees, between those two points as seen from where you are flying.
Context Anchor
Seen on aviation charts, instrument procedures, and navigation data when courses are shown or converted between true and magnetic references.
Derivation
From Latin 'variatio,' meaning 'a difference' or 'a change.' The word captures the idea that the compass reading varies from true direction by a measurable amount that differs from place to place.
Why Pilots Care
Accurate application of magnetic variation prevents navigation errors that could lead to significant course deviations over long distances.
Grounding Statement
At one airport, compass north may be several degrees to the east or west of map north, and that local difference is the magnetic variation.
Intuition Check
Magnetic variation is not the same as compass error in one particular aircraft. Variation is the local difference between true north and magnetic north; aircraft-specific compass error is a separate issue.
Example Sentence 1
The chart showed a magnetic variation of 8° west, so the pilot added 8° to the true course to get the magnetic course.
Example Sentence 2
Sectional charts show lines of equal magnetic variation to help pilots make quick corrections during flight planning.