variation

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variation

compass

Also known as: declination, magnetic declination, magnetic variation, northeasting of the needle(Show More)

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July 14, 2026

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Secular variation refers to the continuous, short-term changes observed in Earth's magnetic field. These changes are crucial for understanding Earth's internal processes and have practical applications.1

A magnetic compass uses a magnetized needle that aligns with Earth's magnetic field to indicate direction. However, Earth's magnetic field is not perfectly aligned with its rotational axis. The difference between true north and magnetic north is called variation, or declination. This variation changes depending on location and over time due to secular variation. Instruments like the declinometer are used to measure this magnetic declination.213

Scientists monitor these changes using magnetic observatories and various instruments, including compasses, dip meters, proton-precession magnetometers, and flux-gate magnetometers. The origin of secular variation is thought to be linked to the dynamo mechanism within Earth's liquid outer core.41

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The lodestone and the compass card
…but is now called the variation or declination. For a time, compass makers in northern countries mounted the needle askew on the card so that the fleur-de-lis indicated true north when the needle pointed to magnetic north. This practice died out about 1700 because it succeeded only for short voyages…
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…but is now called the variation or declination. For a time, compass makers in northern countries mounted the needle askew on the card so that the fleur-de-lis indicated true north when the needle pointed to magnetic north. This practice died out about 1700 because it succeeded only for short voyages…
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magnetism
Repulsion or attraction between two magnetic dipoles
…geographic north is called the magnetic declination (see Earth: The magnetic field of the Earth).
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…geographic north is called the magnetic declination (see Earth: The magnetic field of the Earth).
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magnetic compass
The inaccuracy, known as variation (or declination), varies in magnitude from point to point on Earth. The deflection of a compass needle due to local magnetic influences is called deviation.
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The inaccuracy, known as variation (or declination), varies in magnitude from point to point on Earth. The deflection of a compass needle due to local magnetic influences is called deviation.
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magnetic survey
…magnetic inclination, or dip, and declination (departure from geographic north) at several stations. If the object of the survey is to make a rapid reconnaissance of an area, a magnetic-intensity profile is made only over the target area. If the object of the survey is to delineate already discovered structures,…
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…magnetic inclination, or dip, and declination (departure from geographic north) at several stations. If the object of the survey is to make a rapid reconnaissance of an area, a magnetic-intensity profile is made only over the target area. If the object of the survey is to delineate already discovered structures,…
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Christopher Columbus
The second and third voyages of Christopher Columbus
…discovered the principle of compass variation (the variation at any point on the Earth’s surface between the direction to magnetic and geographic north), for which he made brilliant allowance on the journey from Margarita Island to Hispaniola on the later leg of this voyage, and he also observed, though misunderstood,…
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…discovered the principle of compass variation (the variation at any point on the Earth’s surface between the direction to magnetic and geographic north), for which he made brilliant allowance on the journey from Margarita Island to Hispaniola on the later leg of this voyage, and he also observed, though misunderstood,…
Read More