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Stellar phenomenon
Starspots are stellar phenomena, so named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in general much larger than those on the Sun: up to about 30% of the stellar surface may be covered, corresponding to starspots 100 times larger than those on the Sun.

Observed starspots have a temperature which is in general 500–2000 kelvins cooler than the stellar photosphere. This temperature difference could give rise to a brightness variation up to 0.6 magnitudes between the spot and the surrounding surface. There also seems to be a relation between the spot temperature and the temperature for the stellar photosphere, indicating that starspots behave similarly for different types of stars (observed in G–K dwarfs).

The lifetime for a starspot depends on its size. For small spots the lifetime is proportional to their size, similar to spots on the Sun. For large spots the sizes depend on the differential rotation of the star, but there are some indications that large spots which give rise to light variations can survive for many years even in stars with differential rotation. HD 4915 and HD 166620.

Another activity cycle is the so called flip flop cycle, which implies that the activity on either hemisphere shifts from one side to the other. The same phenomena can be seen on the Sun, with periods of 3.8 and 3.65 years for the northern and southern hemispheres. Flip flop phenomena are observed for both binary RS CVn stars and single stars although the extent of the cycles are different between binary and singular stars.