The above image of the Sun was taken using a filter which allowed only light of wavelength around the wavelegth of the H and K lines of singly ionized calcium (CaII). The ionized calcium very efficiently absorbs radiation and so this is a picture of light produced high up in the Solar atmosphere (essentially in what is referred to as the Chromosphere of the Sun). The blotches that one sees are known as Sunspots. Sunspots are regions of strong magnetic field, average fields on the order of several thousand Gauss. The average field of the rest of the Solar surface regions is 1 to 10 Gauss and the average field of the Earth is slightly less than a Gauss. The intense field, for unknown reasons, makes Sunspots cooler than the rest of the Solar surface. Sunspots have temperatures on the order of 4,500 Kelvins compared to 5,800 Kelvins for the rest of the Sun. Note that Sunspots, although they appear dark on the Sun are actually very, very bright. It is only the comparison to the neighboring regions which makes them appear faint. An individual sunspot may persist for 1 to 100 days.

Sunspot groups can be quite large and are generally long-lived, large groups persist for 50 days (more than a Solar rotation period). The Sun is roughly 100 x larger in diameter than is the Earth; several Earths could fit inside the larger groups.