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Total Solar Eclipse - August 1st 2008

auteur: M.Druckmüller/P.Aniol/ V.Rusin/Novapix

référence: a-sol10-02422

Image Size 300 DPI: 30 * 22 cm

True colors of solar corona What is the color of the solar corona? The majority of people perceive the corona during eclipse as white or slightly greenish-white. However bluish-white, yellowish-white or reddish-white are often reported too. The problem is in the color perception by human vision which is dependent on the definition (calibration) of white color. The less the color differs from white i.e. the less is the color saturated the more critical is the precision of white color calibration. If we use the natural definition that photospheric light is white, we may distinguish very small but still well detectable differences of solar corona coloring. Suppressing the white color component i.e. increasing of color saturation enables detailed study of the color variation throughout the inner corona. It was not easy to create this image. 23 images taken during the eclipse and over two hundred calibration images (dark frames, flat-fields) were necessary to use in order to obtain precise color definition, moreover, blue color of the sky caused by Rayleigh scattering was necessary to remove. Finally the color saturation was increased 50×. From the physical point of view, the image processing suppressed the white color of photospheric light scattered by electrons (K-corona). The green color dominating the innermost part of the corona is without any doubt caused by Fe XIV "Coronium" (530.3 nm) emission and this color visualizes areas of hot plasma with temperature of about 1.8 MK. Obvious is the interpretation of the reddish-pink color of the prominences caused by prominent H-alpha radiation. More complicated is the interpretation of the red color which dominates the outermost part of the processed area. The red shift of the color in the radial direction is probably caused by the increasing significance of the F-corona formed by dust particles scattering the photospheric light. The F-corona, regarded as the continuation of the zodiacal light near the Sun, is of reddish color. The Fe X radiation (637.4 nm) is of red color too and it is probably responsible for the red-purple coloring which is slightly visible on the right side and on the left side of the processed image part. The influence of relatively low altitude of the Sun above the horizon (22°) is worth mentioning too. If we orient the image as it was observed in the sky, it is visible that in the lower part the blue part of the spectrum is slightly suppressed. It is caused by the longer path of the light though Earth atmosphere which filters the shorter wavelengths more intensely than the longer ones. Finally, the answer to the question "What is the color of solar corona?" is that the innermost part of the corona is nearly white with small shift to green especially in active regions which is due to Fe XIV radiation. The color shifts to slightly reddish-white with increasing distance but yellowish-white areas also exist as the yellow color is the mixture of green and red color. Finally the corona disappears in the blue color of the sky in its outer part. In the universe out of the Earth's atmosphere, the corona would continuously extend as zodiacal light which is of a slightly reddish color.

Keywords for this photo:

2008 - ASTRONOMY - COMPOSITE - CORONA - EARTHSHINE - ECLIPSE - MONGOLIA - MOON - NEW MOON - PROMINENCE - SOLAR CORONA - SOLAR ECLIPSE - STAR - SUN - TOTAL ECLIPSE -