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Colors of the Sun

The third contact of the solar eclipse 8/99

Date:11.08.1999 Time:9:32 UT Exposure:1/30s
Field of View:1o x 1.3o Emulsion:Kodachrome 64 Filter:none
Instrument:f=1000mm, 1/10 Place:Altroff, France Observer:T. Credner

© Copyright by the observers

From Colors to Astrophysics

The third contact of a solar eclipse is the moment of first sunlight emerging from behind the dark lunar limb and resembling very nicely a diamond ring. The end of totality is reached. However, this just refers to the light of the dominating bright solar "photosphere".
Close to the second and third contact the red "chromosphere" becomes visible for a few seconds. This atmospheric layer shows an emission line spectrum and emits visible light mainly at the red wavelength of H-alpha (hydrogen). From the chromosphere the prominences occur, ionized gas that is lofted by strong magnetic fields above the solar surface.
All around the sun you can see light of the inner solar corona. In this region of completely ionized gas free electrons are scattering the light of the photosphere. This so called "Thomson scattering" gives a spectrum (and thus a color) almost identical to the one of the mean photosphere. However, in the image above you can see a small color difference between the corona and the direct sun light. It is due to the different spectra on the solar disc itself. The limb of the sun is red in comparison to the whole integrated light of the solar disc.

A. Unsöld, Physik der Sternatmosphären, Springer Verlag