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Images from SOHO, SDO and other sun observatories are often coloured differently for different wavelengths or temperatures: enter image description here enter image description here http://www.nasa.gov/mission_pages/sunearth/science/Sun-Wavelength-Chart.html has statements like "This light is emitted from the upper transition region and the chromosphere and are typically colorized in red."

How is the convention of which temperature or wavelength gets which colour established?

Is it simply so that scientists can immediately tell what temperature or wavelength a picture shows, or are the colours optimized to show particular features?

And why is there a white ring or circle in the sunshade in some SOHO imagery, and why different sizes compared to the disc in the two photos above?

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    $\begingroup$ Better fit for astronomy.stackexchange.com ? $\endgroup$ – Organic Marble Oct 20 '17 at 17:49
  • $\begingroup$ @OrganicMarble Fine by me. Could you please help me move it as I don't think I've enough permission to do that, and better not cross-post? Thanks. $\endgroup$ – Gnubie Oct 20 '17 at 17:58
  • $\begingroup$ The most general rationale is to make it visible at all (since that's outside visible spectrum) and not deceive the reader into thinking this is visible light image. But how the colors are chosen - that's a question for Astronomy.SE $\endgroup$ – SF. Oct 20 '17 at 22:26
  • $\begingroup$ I'm also voting to re-open $\endgroup$ – uhoh Sep 16 '19 at 1:32