Solar magnetic field

Article By:

Sheeley, Neil R., Jr. Naval Research Laboratory, Washington, DC.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.633500

The magnetic field rooted in the Sun and extending out past the planets into the solar system. The field at the Sun's surface is detected remotely by its effect (the Zeeman effect) on atoms whose radiation is observed from Earth. This technique was first applied at the Mount Wilson Observatory in 1908 by G. E. Hale to detect the fields in sunspots. In 1952, H. D. Babcock and his son H. W. Babcock used a scanning technique to make the first magnetic maps of the entire visible disk of the Sun. Their daily “magnetograms” soon revealed a variety of magnetic features, including bipolar regions associated with sunspot groups, and unipolar regions whose fields extend far from the Sun and are responsible for recurrent geomagnetic activity at Earth. The field strengths range from a few gauss (a few hundred microtesla) in quiet areas to 3500 gauss (0.35 tesla) in sunspots. In 1962, the Mariner 2 spacecraft, en route to Venus, made the first on-site sampling of the extended solar field in space. The average field strength was only 50 microgauss (5 nanotesla), reflecting the rapid (inverse square) fall-off of field strength with distance from the Sun. See also: Zeeman effect

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