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Sun in Hydrogen-alpha 2010-08-07 A Composite
by Clif Ashcraft
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Click for larger image |
Videos for this image were taken on July 4th. They show a loop prominence on the northeast limb of the Sun. Two separate videos were recorded using the DMK31 digital video camera. The first recording was made at 1:28 p.m. with exposure settings optimized for the solar disk (1/100th sec). The second video was recorded at 1:35 p.m. EDT optimized for the prominences (1/1000th sec). The bright ring on the solar limb in the composite image is, in fact, the chromosphere which is slightly larger in radius and a lot hotter than the photosphere. |
The photosphere shows pronounced limb darkening. That is real, but exaggerated by histogram stretching in Photoshop. It gives a nice contrast with the more highly exposed chromosphere above it. If the image had been adjusted so that the edge of the photosphere was the correct brightness relative to the chromosphere, no detail would have been visible in the solar disk other than possibly the sunspot. |
The detail on the disk is real, not an artifact of processing. The videos were processed several times, using different wavelet settings in RegiStax, and the dark markings always come out the same. It is unfortunate that the Sun was so quiet, or other prominences would have been seen as dark features superimposed upon the photosphere. When the storms that show as prominences on the limb are seen in top-down perspective on the disk, they are called "filaments". It is probable that a lot of the pink fog above the chromosphere is not real but is caused by scattered light in the imaging system. Each portion of the image was a stack of the best 300 frames of 900 frames in the AVI video file. |
The nice red color of the composite image was created in Photoshop by simply setting the green and blue layer intensities to zero to appear more realistic than the monochrome images produced by the DMK31.
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