A dark zone appearing intermittently on the apparent surface of the Sun (i.e. the photosphere).
Sunspot temperatures are around 1500 K lower than neighbouring regions, and they are associated with an intense magnetic field (detected in 1908 by G.H. Hale, who, during spectroscopic studies of the Sun identified a spectral shift due to the Zeeman effect).
The intensity and movements of these spots follow an eleven-year cycle (the Schwabe cycle, discovered in 1843), which has repercussions on the solar wind and the appearance of aurorae borialis (northern lights). This cycle of solar activity is unexplained.
The spots have been observed for a long time by the Chinese and were identified in 1611 by Galileo. The darkest part is the central region of a sunspot. The penumbra is the filament-like periphery of a sunspot.