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 AR10484 (Zurich class: Ekc, 05° N, 15° W) and AR10486 (Zurich class:
Fkc, 16° S, 57° E) are each approximately the size of Jupiter and represent a most-impressive site through the eyepiece.
Of lesser importance is sunspot AR10485 (Zurich class: Bxo, 07° S, 08° E) immediately to the north of AR10486 which
represents the only other major source of activity. Further details for these active regions are available
here.
Note: When looking at the sun before it crosses the meridian, East is always to the left and
West is always to the right and vice versa when the sun does cross the meridian.
Body: Sun Mass: 332,900 x Earth Mean Eq Diameter: 109.1 x Earth Distance: 152 million km RA / Dec: 13h 57m 41s / -12° 01' 32" Diameter: 32.17' Magnitude: -26.8 Light Time: 0h 8m 21.6s |
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Date: Oct 25, 2003 13:10:23 UT+3 Location: Athens, Greece Equipment: Celestron 14" SCT Losmandy G-11 GEM TeleVue 55mm Plossl TeleVue DEC-0028 Adapter Nikon Coolpix 995 Baader ND-5 (full-aperture) Exposures: 1 x 1/265 sec @ f5.8 ISO Auto JPG RGB Fine image format 2048x1536 image size Autodark subtraction Software: Photoshop V6 Processing: Unsharp Masking Grayscale Brightness/Contrast Gaussian Blur Resampling (30%) JPG Compression |