| sunspot |
|
A region on the Sun where the temperature is lower than that of the surrounding photosphere. Sunspots thus appear relatively dark. The presence of a strong magnetic field, concentrated in a spot area, produces the cooling effect. Sunspots can occur individually but often form groups or pairs of opposing magnetic polarity. In the dark central part of the sunspot, the umbra, the temperature is about 3,700 K compared with the 5,700 K of the photosphere. The outer and brighter part of a sunspot, the penumbra, consists of aligned bright grains on a darker background which are arranged radially around the spot. See also: solar activity, butterfly diagram, Wolf sunspot number. |