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Measuring the Earth's Magnetic Field


Little was known about magnetism and the Earth’s magnetic field until last centuries. However, early observations of magnetic materials date back to the ancient Greeks and Chinese who observed mineral stones that attracted each other. In 1600, William Gilbert published “De Magnete”. The book is considered as the starting point for the scientific study of terrestrial magnetism. Thanks to his experiments, Gilbert concluded that the Earth itself was a giant magnet. 

Magnus magnes ipse est globus terrestris. (The Earth itself is a great magnet.)

— William Gilbert, De Magnete

In 1835, Carl Friedrich Gauss was the first to measure the Earth’s magnetic field strength, which ranges from less than 25 microteslas (µT) around the middle of the globe to over 60 µT around both magnetic poles. Other standard units used includes Gauss, being the Earth’s magnetic field strength of around 0.25 to 0.60 G.

A complete representation of the Earth’s magnetic field at a given location requires a vector with three coordinates, that can be Cartesian (north, east, and down) or spherical (declination, inclination, and intensity). With the latter, the direction of the North magnetic pole can be obtained using a compass. Its relative angle to the true North pole is the declination. The inclination is the angle the field makes with the horizontal when facing the magnetic North.


A British watchmaker, George Graham, was the first one to note rapid changes in the magnetic declination of the Earth’s magnetic field 300 years ago. Since then, there was growing evidence that the Earth’s magnetic field exhibited some disturbances on short time scales. Since then, many scientists have been doing daily measurements of the Earth’s magnetic field in different locations. There are different observatories with very sophisticated instruments, such as satellites around the world in charge of monitoring Earth’s magnetic field. For example, INTERMAGNET (International Real-time Magnetic Observatory Network) is a world-wide consortium of institutes operating ground-based magnetometers recording the absolute level of the Earth's time-varying magnetic field.


However… Do you know we can measure Earth’s magnetic field with a simple smartphone? Join us, SiM, on creating our own world-wide consortium that measures the Earth’s magnetic field. MagnetiSiM 2022 will offer you the instructions to measure these values and share it with all of us.

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