This investigation proceeds from the microscopic structure inside a magnet, through planetary processes, to the interaction between Earth and the Sun. Gravity has no poles, because the gravity from every part just adds together, and magnets are different. Every magnet has a north pole and a south pole, and opposite poles attract each other while the same poles push each other away. A magnet attracts other magnets, and it also attracts some iron and steel things, such as pins and paper clips. Two kinds of magnets exist, permanent magnets and temporary magnets. Here is a rule to keep: magnets are not for mouths or small children, since loose magnets can hurt children if they are swallowed. If a child swallows more than one, the magnets can pull together inside the body and cause serious damage.
In a permanent magnet, tiny magnetic regions called domains line up in the same direction. The domains in a piece of ferromagnetic material are usually between 0.1 mm and a few mm in size. Magnetic domains form because the electron waves can lower their energy when nearby spins line up. Ferromagnets tend to stay magnetized to some extent after being subjected to an external magnetic field. If you heat up a permanent magnet, the domain walls tend to come loose and the net magnetism goes away. The Curie temperature of iron is about 1043 K, and it gives an idea of the amount of energy it takes to break up the long-range ordering in the material. Permanent magnetization cannot occur above about 650 degrees Celsius (1,200 degrees Fahrenheit). If all the spins in a piece of iron were aligned, the field would be about 2.1 tesla. Very strong rare-earth magnets have been made from alloys of samarium or neodymium with cobalt.
Magnetism is caused by the motion of electric charges, and in space, on the Sun and in Earth's core, electric currents are the only source of magnetism. In 1820 Hans Christian Ørsted's discovery showed that electricity and magnetism are related. William Sturgeon built the first practical electromagnet, strong enough to support 20 times its own weight, and Joseph Henry, following Ørsted and Ampère, introduced the electromagnet. In 1831 Michael Faraday discovered electromagnetically induced currents, which depend on the rate at which the field changes. Electromagnets are not permanent, but they can be far stronger than the strongest permanent magnet. As of November 2026, the MagLab's most powerful non-destructive magnet generates a field of 100 tesla. Superconducting materials expel magnetic fields as they transition to the superconducting state, and in a Maglev train, superconducting magnets suspend the train car above a U-shaped concrete guideway while the powered guideway drives the train.
Early Chinese compasses were oriented to point south rather than north like today's compasses, and miners in search of jade appear to have used south-pointing spoons. A lodestone compass was used in navigation as early as 1086. In time, 32 points of direction were added to the compass card. Edmond Halley carried out the first magnetic declination survey and published a chart of his findings two years later, and he used his view of the planet to explain why magnetic declination slowly changes over time. Magnetic declination is the angle between magnetic north and true north, and it is unreliable near the poles, and at the magnetic poles a compass does not show direction. Some compasses, such as a solar compass that uses the Sun, do not use Earth's magnetism to indicate direction. As of November 2026, receivers from the global positioning system (GPS) have begun to take the place of compasses.
The planetary investigation begins in the deep interior, and the evidence about it is largely indirect, which is why interpretation matters. Earth is a really big magnet, and its magnetic field begins in its core, some 2900 km below the surface. The motion of electrically conducting iron in the outer core makes electric currents, and those currents generate the field. The process by which electric currents in the core generate magnetic fields is self-sustaining so long as an energy source maintains convection. Direct observations of Earth's magnetic field extend back just a few centuries, so scientists rely on indirect evidence, and magnetic poles are defined as the area where the dip angle is vertical. The position of Earth's magnetic north pole was first precisely located in 1831, and as of November 2026 it is moving, a gradual shift that must be regularly accounted for in navigation.
During a pole reversal, Earth's magnetic north and south poles swap locations. The field weakens but does not completely disappear, and it becomes jumbled, so multiple magnetic poles can emerge in unexpected places. The last reversal was about 750,000 to 780,000 years ago, and consecutive reversals have been spaced from 5 thousand years to 50 million years apart. Even if Earth's field were beginning a reversal, it would take several thousand years to complete. Excursions happen about 10 times as frequently as reversals, although excursion events are generally regional, rather than global. In the past 200 years, Earth's magnetic field has weakened about nine percent on a global average, as of November 2026, but scientists have no reason to believe a pole flip is imminent. Plant and animal fossils from the period of the last major reversal do not show any big changes, and there is little scientific evidence of any significant links between Earth's drifting magnetic poles and climate.
At the largest scale, Earth's field interacts with the Sun, and the consequences range from brief, insignificant intrusions to disturbances that matter for astronauts and pilots. Earth is surrounded by a large magnetic shield called a magnetosphere, and it protects us from harmful charged particles in space. The Sun sends out a flow of charged particles called the solar wind, which creates temporary cracks in the shield, letting some energy reach Earth's surface daily. Since these intrusions are brief, they do not cause significant issues, but a magnetic storm is a period of rapid magnetic field variation, and occasionally the Sun's magnetic field directly links with that of the Earth. Astronauts and high-altitude pilots might be subjected to increased radiation during a magnetic storm. Sunspots consist of glowing hot gas, yet they are all intensely magnetic. Mercury, Jupiter, Saturn, Uranus and Neptune all have magnetospheres, and all but Mercury's dwarf Earth's.
Words to know
- ferromagnetic: strongly magnetic
- convection: heat-driven flow
- declination: compass angle
- magnetosphere: magnetic shield
