Perhaps the most obvious feature of the sun is the sunspots that characterize the photosphere. The base temperature of the 300-km deep photosphere is approximately 6400 °C whereas the sunspot regions are characterized with areas of relatively lower temperature (around 4800 °C for the umbral regions and 5900 °C for the penumbral regions) and increased magnetic activity (up to 3000 times the average magnetic field of the sun). Due to the differential rate of rotation of the solar disk (26 days at the equator and 36 days at the poles), there is a "twisting" of the magnetic fields which surface to the photosphere producing sunspots. Typically, these spots and groups are found to lie + 30° of the solar equator and can physically be many-fold times larger than our planet! As the images below indicate, sunspots are characterized with a dark core, the "umbra", where the temperature is about 1600 °C less than the surrounding temperature of the photosphere whereas the less darker envelope which typically encompasses the umbral region, the "penumbra", is about only 500 °C less than the surrounding photospheric temperature.

Studies have shown sunsplot activity to exhibit an eleven-yr cycle with virtually little sunspot activity during the minima of the cycle whereas frequent sunspots and associated groups dominate during the maximum of the same cycle, typically approximately 4.5 years after the minimum. During the solar maximum, we also have frequent filaments, flares and prominences (see here) which include ejected material from the sun's outermost "shell", the chromosphere, that reaches earth causing, for example, geomagnetic storms that produce the well-known and beautiful aurora borealis and australis.

Note: The sunspot group AR 3256 in the image below is the most dominant group on the Sun (Zurich class: Eho; 23° S, 21° W) and is capable of beta-gamma flares. The other prominent groups visible in the image below are AR 3260 (Zurich class: Cso; 23° N, 08° W), AR 3176 (Zurich class: Esi; 19° N, 43° W), AR 3257 (Zurich class: Hax; 27° S, 11° W), AR 3262 (Zurich class: HSX; 19° S, 30° E) and, finally, AR 3264 (Zurich class: HSX; 16° N, 56° E). Further details for these active regions are available here.