Sunspots are visible areas of the sun's surface, the photosphere, caused by very strong magnetic fields. Relatively small spots, measuring about 150 miles, may exist for less than one hour while spots 50,000 miles across can remain for six months. The quantity of sunspots varies over a predictable, eleven year cycle, as does other solar activities such as the level of ultraviolet emission. The sun is presently entering a period of increased sunspot activity. Our student researchers are using the sunspot number as one indicator of changes in the solar cycle.
Sunspots usually appear in pairs or groups.
A spot frequently has a darker interior called an umbra, and a lighter outer area, the penumbra. These sunspots appear dark because they are relatively cooler than the gaseous material surrounding them. A high resolution sunspot image reveals these features clearly. Viewing sunspots is simple and great fun when using the Astroscan 2001 Wide Field Telescope with an attached sun viewing screen from Edmund Scientific . However, a precise count of the day's sunspot number can not be made with such small, solar observing telescopes.