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 AR10960 (Zurich class: Fkc, 7° S, 62° E) is quite a prominent group
against the solar disk and has the potential for strong X-class flares due to the "Beta-Gamma-Delta" magnetic field
which has developed. Of much lesser importance is the sunspot group AR10959 (Zurich class: Cso, 12° S, 36° E) to the
west. Further details for these active regions are available
here.
Body: Sun Mass: 332,900 x Earth Mean Eq Diameter: 109.1 x Earth Distance: 152 million km RA / Dec: 04h 43m 53s / +22° 17' 14" Diameter: 31.54' Magnitude: -26.8 Light Time: 0h 8m 27.4s |
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Date: Jun 03, 2007 12:15 UT+3 Location: Athens, Greece Equipment: AP 160 f/7.5 StarFire EDF AP1200GTO GEM Canon EOS 300d Baader UV-IR/Cut Baader ND-5 (full-aperture) Exposure(s): 1 x 1/500 sec ISO 100 RAW image format 3072x2048 image size Manual Mode Software: Photoshop CS2 Processing: Grayscale Unsharp Masking Brightness/Contrast Levels Resampling (40%) Cropping JPG Compression |