Sunspots Sunspots are the most well known feature on the photosphere. They are a region of the solar surface that is dark and relatively cool; and has extremely high magnetic field. Sunspots appear dark when seen against white light because they are giving off less radiation per unit area than the photosphere. Thus, they are relatively cool (around 2000K cooler) since cooler gas radiates less than hotter gas). Actually if would somehow remove a sunspot from the solar surface and put it off into space, it would appear bright against the dark sky, a large one would give off as much light as the full moon as seen from the Earth. If you follow sunspots everyday, you would be able to measure the rotation rate of the Sun.

Sunspots occur when the magnetic field loops out Figure 11.16 Sunspots occur when the magnetic field loops out of the photosphere

Sunspot Cycle Minimum number Maximum number 2001-2002, year with greatest number of sunspots. Number of sunspots will decrease until 2006 and will rise again to a maximum in 2012. 11 year cycle. Minimum number Maximum number

Prominences Filaments Figure 11.18a Filaments Flares

Sunspots