What Color is the Sun?

A comment from a friend got me thinking on this topic... One scientific answer is that the Sun is white by definition. Visual observation of the Sun is unsafe without a filter. Photographic neutral density filters preserve colors, but don't provide enough reduction to be safe for visual use. Filters safe for visual use come in many colors commonly green, yellow orange, and blue.

You can see typical colors in my tests of white light solar filters. For use with a telescope, filter colors depend on the material the filter is constructed with. High quality glass filters often use Nickle-Chromium depositions which give a yellow-orange color. I've seen thin film filters range from the pale yellow of the Thousand Oaks RG film to the blue-violet of the Baader AstroSolar film filters.

Detailed white light astrophotographs of the Sun are often monochrome either black and white or black and yellow-orange. There is little perceptible color on the sun, so monochrome cameras and images work well.

When the sun is dimmed enough by dust or pollution for people to perceive color it is usually naturally filtered to the yellow to red end of the spectrum. I put down the preference, that many have for a yellow-orange color scheme, as due to fond memories of beautiful dust filtered sunsets or primary school drawings with yellow suns.

Jet gets a close view of Solar Eclipse
A passing jet gets a close view of the partial eclipse of 2014-10-23 at 5:55 CDT in Austin, Texas. Questar 3.5" with Sony NEX-5N at prime focus ISO 200 for 1/60 sec. Deconvolved in Lynkeos, final adjustments in Photoshop. The plane is about 60 miles away.

Studies of human perception give a scientific reason to prefer colored white light Suns. Details in a white light image of the Sun are very low in contrast. Even the darkest sunspots would shine like Venus, if they were alone in the sky. Human visual perception of detail depends on both intensity (luminance contrast) and color (chrominance contrast). Remember the days of monochrome CRT computer monitors? Green or yellow on black were common, improved readability, alternatives to black and white monitors. Adding color contrast to white light luminance data could improve the perception of low contrast detail in solar images.

Individual perception and preference for colors varies widely. What works for someone else may not work for you. I'm pleased that there is a plausible scientific rationale for my very emotional pleasure in yellow-orange images of the sun. The eclipse image above used a nickle-chromium yellow-orange tinted filter. I still prefer glass yellow-orange filters for visual observation. For photographs, I shoot images with a thin film filter and change the blue-violet colors it produces in post processing to match those colors, as in the image below.

ISS Solar Transit
The International Space Station transits the Sun passing by sunspot group AR2585 from Briggs, Texas. Questar 3.5 telescope with Sony a6300 shooting 30 fps 4k video at prime focus. Exposure 1/320 sec at ISO 200. 2016-09-04 19:15 UT. Video frames deconvolved in Lynkeos, then composited and exposure adjusted in Photoshop.

My take away is: choose the colors that you find pleasing and convince yourself that there is sound science behind your choice :-)

Content created: 2017-02-07




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