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 groups AR10501 (Zurich class: Dko, 03° N, 05° E) and AR10507 (Zurich class: Eki, 10° N, 62° E) are quite visible against the solar disk and have the potential for strong X-class flares. Of lesser importance is the sunspot group AR10506 (Zurich class: Dso, 21° S, 59° E) immediately to the south of AR10507 and which is characterized with an impressive plage. Further details for these active regions are available here. Similarly, for an image of today's eastern limb by the author, please click here.

Note: There is some confusion as to the numbering/renumbering of these active regions which are making their second pass around the sun. Sunspot group AR10484 is also known as AR10501; sunspot group AR10486 is also known as AR10506; and, finally, AR10488 is also known as AR10507. Some SOHO imagery is currently using the original numbering whereas other SOHO imagery is based on the renumbered sequence.