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 AR10786 (Zurich class: Dac, 12° N, 35° E) is quite prominent against the solar disk and has the potential for strong X-class flares. Of lesser importance are the sunspot groups AR10782 (Zurich class: Cao, 18° S, 57° W) to the southwest and AR10789 (Zurich class: Hsx, 18° N, 74° E) to the northeast which are characterized with impressive plages. Further details for these active regions are available here.
332,900 x Earth
Mean Eq Diameter:
109.1 x Earth
152 million km
RA / Dec:
06h 58m 39s /
+22° 45' 24"
0h 8m 27.4s
Jul 05, 2005
AP 160 f/7.5 StarFire EDF
Losmandy G-11 GEM
Canon EOS 300d
Baader ND-5 (full-aperture)
1 x 1/500 sec
JPG FINE image format
3072x2048 image size