Compasses point towards the north due to the interaction between the Earth's magnetic field and the magnetic needle of the compass. The needle aligns with the lines of force of the magnetic field, providing an indication of the north-south direction.
The geographic North is simply where all our meridians meet: right at the top of the Earth, on the axis of rotation of our planet. The magnetic North, on the other hand, depends on the Earth's magnetic field, in other words, the immense natural magnet hidden at the core of our planet—and it does not occur at the same location at all! The result? The two "Norts" are offset by about 500 kilometers, which corresponds to an angle called magnetic declination, varying depending on your position on the globe. It is this discrepancy that causes your compass to never point exactly to the "true North" on maps, but rather to a slightly shifted north, the magnetic North.
The Earth's magnetic field mainly comes from convection movements in the liquid outer core of our planet. Composed primarily of molten iron and nickel, this hot metallic liquid is constantly moving, driven by the heat emitted from the solid inner core. These movements generate powerful electric currents, which in turn produce the magnetic field. The phenomenon has a cool name: the dynamo effect. You can think of it as a massive dynamo located at the center of the Earth, creating a magnetic field that completely envelops our planet. Without this magnetic protection, life would be severely exposed to cosmic radiation.
The compass works thanks to a small magnetized needle that is free to pivot on itself, which will naturally align according to the invisible lines of the Earth's magnetic field. Since the Earth acts a bit like a huge magnet, it attracts the magnetized end of the needle — often painted red — thereby indicating the magnetic north. The needle then points approximately in the direction of north, making it easy to identify the other cardinal directions. Simple but effective: as long as nothing disrupts the magnetic field, it always does the job.
Unlike what you might think, the magnetic north does not stay in place. It is constantly moving, about fifty kilometers per year. Currently, it is sliding from Canada towards Siberia. It is the unpredictable movements of the molten liquid iron located at the Earth's core that create these changes. This drift forces certain regions to regularly adjust their maps so that compasses point to true north. Moreover, scientists are closely monitoring this to anticipate and adapt to these variations.
A compass is reliable, but sometimes it has a mind of its own. Several factors can disturb the needle. For example, the presence of metal objects or magnets nearby can strongly interfere by creating their own local magnetic field. Similarly, certain types of magnetic rocks, like magnetite, found in some regions of the globe, slightly alter the indicated direction. Even large power lines or electronic devices can generate strong enough magnetic fields to temporarily influence your compass. Finally, during solar storms, the intense activity from the Sun briefly disrupts the Earth's magnetic field: as a result, your compass can become disoriented.
Some animals, such as birds, sea turtles, and even certain bacteria, use the Earth's magnetic field to orient themselves and navigate during their migrations.
The magnetic north does not exactly coincide with the geographic north. Currently, this point is located in Canada and moves approximately 55 km per year towards Siberia.
The first users of compasses were Chinese navigators as early as the 11th century, long before Christopher Columbus and European explorers!
On Mars, the global magnetic field is almost non-existent today, making traditional compasses useless on this planet.
Magnetic declination varies depending on your location and time period. Some compasses have a mechanism to adjust this declination directly. You can find up-to-date values in official geomagnetic databases or on recent topographic maps, and adjust your compass accordingly, thereby improving the accuracy of your navigation.
Near the magnetic North Pole, the lines of the Earth's magnetic field become nearly vertical. As a result, a standard compass with a horizontal needle may struggle to function properly or provide an accurate indication of north. Special instruments, such as inclinometer compasses, are necessary for navigation in these areas.
Ferromagnetic metal objects such as mobile phones, computers, keys, metal watches, as well as electronic devices emitting magnetic fields (speakers, electric motors), can influence and distort the magnetic needle of your compass.
The magnetic north is related to the movements of liquid iron in the Earth's outer core. These chaotic movements generate the Earth's magnetic field, the position of which changes continuously, resulting in a slow displacement of magnetic north by about several kilometers per year.
The maps indicate true north, which corresponds to the Earth's axis of rotation. However, a compass points to magnetic north, defined by the Earth's magnetic field, which has a slight offset known as magnetic declination. This declination varies depending on your geographical location and changes slowly over the years.
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