5. Magnetogram of Active Region and Sunspot Pairs

Observations of sunspots show that they often appear in groups, forming complex active regions (top left close-up; the rationale behind the name "active region" will become apparent in later slides).

Solar Disk image
03 July 1991: Magnetogram image.

Sunspot are almost never seen in complete isolation, but instead are most often grouped in pairs of opposite magnetic polarities (bottom close-up). Isolated sunspots pairs tend to line up in the East-West direction (approximately from left to right on this magnetogram). Further scrutiny of magnetograms such as this one reveals that the magnetic polarities of sunspot pairs located in the northern and southern solar hemispheres are reversed; in one hemisphere the negative magnetic polarity sunspot almost always leads the positive polarity sunspot (with respect to the westward apparent motion due to solar rotation), while a similar behavior, except for reversed magnetic polarities, is observed in the other hemisphere. This intriguing large-scale pattern is a direct manifestation of the operation of the solar dynamo, the mechanism through which the solar magnetic field is cyclically regenerated.

Written By P. Charbonneau and O.R. White–April 18, 1995