Prof. Kathy Whaler – Why the compass needle points North

Magnetic compasses may have been used by the Chinese as early as the first century AD, and natural magnets were known to the Greeks in classical times. The first scientific treatise ever written is generally recognised as being Petrius Peregrinus’ geomagnetic text ‘Epistola de Magnete’ in 1269. This was followed in 1600 by ‘De Magnete’ by William Gilbert, physician to Queen Elizabeth I, who wrote (in Latin!) that ‘the Earth globe itself is a great magnet’. Among other famous names involved in the study of geomagnetism are Edmund Halley (of comet fame), who is thought to be the first ever to draw a contour map (of the angle between true and magnetic North over the Atlantic Ocean), and Carl Frederich Gauss, who was heavily involved in the development of instruments to measure the magnetic field, began establishing a network of permanent geomagnetic observatories, and was the first to represent the field in mathematical form. 

Knowledge of the magnetic field has been routinely used in navigation (and measurements have routinely made) since the 18th century, soon after Henry Gellibrand discovered that it changed with time. 

Nowadays, the geomagnetic observatory network is supplemented by measurements from space – in November 2013, ESA launched a constellation of three low-Earth orbiting magnetic satellites. Why? – partly because we still need to monitor the magnetic field and its changes, but also because fundamental questions remain about its origin and the energy sources that maintain it. We know that the field originates in the liquid iron region of the deep Earth, and have plausible mechanisms for how it is generated which match most of the observations, including that over most of Earth history is has pointed approximately towards either the North or South pole. 

Kathy Whaler has been Professor of Geophysics at the University of Edinburgh since 1994. Her main research interests are using permanent geomagnetic observatory and low Earth orbit magnetic satellite data to study the origin and maintenance of the Earth’s magnetic field; the magnetic field of the near-surface rocks of the Earth and other solar system objects that reflects their composition and past history; and using electromagnetic induction to probe the electrical resistivity structure of the crust and upper mantle, particularly as part of multi-disciplinary projects in rifting environments. She is a Fellow of the Royal Society of Edinburgh and of the American Geophysical Union, a Past President of the Royal Astronomical Society, and was awarded the Royal Astronomical Society’s Price Medal.

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