What will change by several minutes of arc each year at most locations?

What will change by several minutes of arc each year at most locations?

• A. Local variation
• B. True north direction
• C. Geographic north
• D. Magnetic dip

Answer: (A)

Magnetic variation at a location changes gradually over time because the Earth's magnetic field is not fixed; the fluid motion in the outer core slowly shifts the alignment of magnetic north relative to geographic north. This changing angle between true north and magnetic north is called local variation (magnetic declination), and it typically drifts by a few minutes of arc each year at many locations. That steady, location-specific drift is what navigation charts update to keep compass readings accurate. In contrast, true north direction and geographic north are fixed references tied to the Earth's geographic axis, and while magnetic dip (inclination) does change over time, the question points to the annual drift in declination, which is the hallmark of local variation.

Magnetic variation at a location changes gradually over time because the Earth's magnetic field is not fixed; the fluid motion in the outer core slowly shifts the alignment of magnetic north relative to geographic north. This changing angle between true north and magnetic north is called local variation (magnetic declination), and it typically drifts by a few minutes of arc each year at many locations. That steady, location-specific drift is what navigation charts update to keep compass readings accurate. In contrast, true north direction and geographic north are fixed references tied to the Earth's geographic axis, and while magnetic dip (inclination) does change over time, the question points to the annual drift in declination, which is the hallmark of local variation.