One of the first major discoveries made at Mount Wilson Observatory was in determining that sunspots were magnetic in nature. Observations of sunspots show that they often appear in groups, forming complex active regions. Sunspot are almost never seen in complete isolation, but instead are most often grouped in pairs of opposite magnetic polarities. Magnetic polarities of sunspot pairs located in the northern and southern solar hemispheres are reversed.
The picture to the left, taken by the Yohkoh satellite in X-rays in 1992 near the sunspot maximum, shows these magnetic loops clearly. In the photograph at left, streams of material surrouding the upper sunspot appear to be spiraling in with a counter-clockwise motion, while for the lower sunspot, the similar is in a clockwise direction.