If the latitudes and durations of these sunspot groups are plotted against time, they produce a 'Butterfly Diagram' . In the last 100 years the period of rise has ranged between 3.3 and 5.0 years and the period of fall between 5.7 and 8.3 years, so it is difficult to make predictions over any length of time. These disturbed regions are seen as dark markings on the Sun's surface. The life of a Sunspot can be as short as a few hours or as long as several months. Some are seen over several revolutions of the Sun about its axis, and in such cases can actually be observed for only about half their duration, because for 13 or 14 days of the 27 day revolution they are on the hemisphere facing away from the Earth.
Sunspots can occur singly and in groups, and they can be of very different sizes.
Large Sunspots are sometimes visible to the naked eye, when seen through fog, or when the Sun is dim and red at sunrise or sunset. At other times the disk is too bright to be looked at directly. Sunspots with areas of only one millionth represent the other end of the scale. The disk can be seen to get less bright at its edge. This is called limb darkening.