Bar magnets have two poles. They make dipole magnetic fields. Magnetic fields can have more than two poles. Quadrupole fields have four poles.
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Original artwork by Windows to the Universe staff (Randy Russell).
Dipole, Quadrupole, and Multipole Magnetic Fields
Have you ever seen a bar magnet? Bar magnets have two magnetic poles - north and south. The magnetic field around a bar magnet is called a dipole magnetic field. "Dipole" means "two poles".
Bar magnets are not the only things that make dipole fields. Electricity flowing through a coiled wire can cause a dipole magnetic field. The magnetic fields of some planets are pretty much dipole fields.
Dipoles are not the only shape magnetic fields come in. There are also quadrupole fields with four poles. Sometimes magnetic fields have six or even eight poles (an octupole!). Any field with more than two poles is called a multipole field.
Some planets, stars, and moons have magnetic fields. Some of those magnetic fields are pretty much dipoles. Others are more complex. They have a mix of dipole and multipole magnetic fields. The magnetic fields of Earth and Jupiter are mostly dipoles. They only have weak multipole parts. Uranus and Neptune have more complicated magnetic fields. The quadrupole parts of their fields are just as strong as the dipole parts!
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