For star color, use the B-V index. This is the difference in magnitude as measured in the blue and visual photometric wavebands. Spectral type is not a reliable indicator of color for two main reasons: The heavy element composition of a star alters the color, such that greater 'metallicity' makes for a redder color; and interstellar dust on the line of sight induces reddening.
The B-V index is a far better indicator of color. The larger this value, the redder the star. Zero is very slightly bluish. -0.34 is about as blue as it gets, but still not *obvious* blue; just bluish. Our Sun, at 0.62, is yellow. 1 is getting to a golden-orange. 2 is orange. The reddest carbon stars (or those heavily reddened by much dust) get to around 5 or so, which is not stoplight red, but a lovely orange-red.
A simple algorithm could be constructed by which to differentially alter RBG values. Or a lookup table could suffice. Differentiating to no more than 8 discrete color values is *amply* sufficient.
As to star brightness, as you likely know each magnitude change is a briggtness difference of 2.512. This was derived so that 5 magnitudes is a 100-fold brightness difference, which corresponds well with the logarithmic response of vision.
As noted up-thread, a magnitude limit of about 6.5 is good for wider FoVs. However, when zooming in, the result will feel intuitively odd if the stars remain at a fixed limit and of fixed size. I feel that altering the star numbers, brightness limit and hence dot size will pay dividends. Rather like what happens when using optical aid, such as a binocular. A small bino, e.g., a common enough military 6X30, will reveal stars some 2.5 magnitudes fainter than will one's eyes alone. And note that said instrument has an FoV of about 10 degrees. A complete 9th magnitude star database would serve nicely for expanding on a wide FoV limit of about 6.5, increasing to 9 when zooming in to 10 degrees.
When considering adopting a dark sky naked eye limit of 6.5, this admits the potential for inclusion of the milky way. Particularly in the northern summer season (southern winter), for the bright central portion of our Galaxy is on display, and is so easily seen on dark nights even well before one is fully dark adapted. From a darkened cockpit at altitude, it's one of nature's grand spectacles.
I would recommend a low resolution bitmap, with pixels no larger than 0.1 degree. This would be a strip chart (360 x 60 degrees) of 3600 x 600 pixels. Why such comparatively poor resolution? Because at such low image surface brightness our visual system operates at *tens* of times worse resolving power than under daytime light levels. Better to simulate that than to present an image of unrealistic photographic sharpness. As any amateur astronomer like myself (decades of experience) will amply confirm.
Furthermore, the milky white ay is too dim to elicit a color response. And so no fancy coloring like a photo will reveal. Make it a monochromatic pale bluish, said cool color tone suggesting nocturnal dimness. And of course the color must blend with that of the sky. Suggesting that the same general cool hue be adopted for a dark sky itself.
And about the night sky. It's never truly black, even in space. Sunlight scattered by interplanetary dust (from comets and bashing asteroidal bodies over the aeons) actually adds a little to night sky illumination. And the Earth's airglow layer, at about 100km up, adds even more light than that for us down below. The darkest sky, by *far*, is under heavy cloud cover. All in the absence of artificial lighting, of course.
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Topic: Stars (Read 4911 times)
