"Dawn simulators" are used to simulate a natural sunrise, or at least the physiological effects of one.

What temporal sequence of color values (e.g., hue, saturation, brightness, and timing) corresponds to a typical spring or summer sunrise? Are the methods for calculating changes in these values based on season?

  • $\begingroup$ This sounds like an interesting research project: find pictures or video of sunrises (and sets?) and do an HSV analysis on them (assuming you're happy with the way cameras capture colors, which is slightly different from how the human eye does it). I think the color of the pre-sunrise sky at a given point is entirely dependent on its elongation (degree distance) from the Sun. $\endgroup$
    – user21
    Oct 30 '14 at 12:59
  • $\begingroup$ @barrycarter: Another approach I might try is to run a sunrise in a simulator (like Starry Night) and get the color values off of the image of the sun on the screen. But I'm not sure whether that will give me what I'm looking for, either from an astronomical perspective (is capturing the sun's color in such images really what I'm looking for?) or a computer-graphical one (how do I capture the right pixels?). $\endgroup$
    – orome
    Oct 30 '14 at 15:41
  • $\begingroup$ I think programs like Starry Night and Stellarium use fairly simple and inaccurate algorithms for dawn/dusk. For example, Stellarium shows noticeable darkening during a partial solar eclipse: in real life, the darkening is minimal. Capturing pixels is easy, but you could also read the source code. I'd use many real life images, get the RGB of the pixels and create some sort of model. This would be project-level work. Of course, even pre-sunrise, the Sun can create glare and reflections leading to imperfect camera captures. $\endgroup$
    – user21
    Oct 30 '14 at 15:51
  • $\begingroup$ @barrycarter: Yes, that's what I'd be concerned about. Also it does sound like quite a project. This information must be around somewhere. $\endgroup$
    – orome
    Oct 30 '14 at 15:57
  • $\begingroup$ You could ask ipl.org or do some intense googling or even look for "dawn" in images.google.com to get a head start. $\endgroup$
    – user21
    Oct 30 '14 at 15:59

These steps are in there for credit

I used Stellarium to simulate a sunrise, and took screenshots of the progression. Each screen shot was 2 seconds apart, and stellarium was accelerated to 10 minutes a second.

Then, using imagemagik to crop batch those 13 images with this command:

mogrify -crop 1280 1024 *.png

(those numbers are the size of my screen. I cropped to get rid of my second screen)

Next I put the images into Color Thief and got the pallet of each image. This is the result of those 13 images:

Those are the colour pallets. You can pick whatever colours you want from them with a colour picker, such as KColorChooser.

  • $\begingroup$ Thanks. I'll see what I can make of these. I think the thing to do though is capture the sun itself, but careful selection from these palettes may give the right result too. $\endgroup$
    – orome
    Nov 2 '14 at 17:26

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