Figure 16-17: R I V U X G
Sunspots (a) This high-resolution photograph of the photosphere shows a mature sunspot. The dark center of the spot is called the umbra and has the lowest temperature. It is bordered by the penumbra, which is less dark, is hotter than the umbra, and has a featherlike appearance. (Even the umbra emits visible light, but not enough to capture in an image against the glare of the Sun.) (b) In this view of a typical sunspot group, several sunspots are close enough to overlap. In both images you can see granulation in the surrounding, undisturbed photosphere.

(a: Scharmer et al., Royal Swedish Academy of Sciences/Science Source; b: NOAO)