Fortunately, Philip noted that he slightly enhanced the image. Perhaps stars can become as blue as he depicts, but even this is still a desaturated blue, but stars simply do not get hot enough to produce a deep blue, as can be found in the deeper blue skies seen, perhaps, from mountain tops or on especially clear and calm days. Ironically, white dwarfs -- not stars by definition --might be hot enough to appear a deeper blue than what is shown in the APOD imaage, though they fade to white and, eventually, become dark.Ann wrote:The picture that Philip Hart posted in the discussion thread, where he had applied no increase in contrast, saturation and vibrance, makes the color of Spica to appear very "normal-blue-sky"-like to me.
I agree that at some point as we approach a distant star its light flux will max-out all our color cones so that any one color could not be distinguished from the other colors; white is all that would be seen. This is true of the Sun, though some side effects besides atmospheric extinctions can cause some to see the Sun as yellowish-white.However, the surface brightness of hot stars is so very much higher than the surface brightness of cool stars. A high surface brightness will burn out the impression of color in the human eye. Personally I believe that the color of hot stars gets "burnt out" to the human eye much more easily than the color of cool stars.
Our color cones -- rods refer to the non-color receptors -- are only part of the overall color processing equation. Remarkably, this processing compensates for the small percentage of blue color cones. The receptivity charts of the retinex (eye-brain per Dr. Land) reveal that blue is weaker than the other colors, but not significantly so.But as Chris pointed out, the human retina contains far fewer blue-sensitive rods than red- and green-sensitive rods.
This may be tested by using averted vision on the really hot stars like Rigel, or perhaps Spica,too.This is an important reason why it is hard for us to see blue color in stars. The light that reaches us from the stars is faint and concentrated (the light seems to emanate from a single point in the sky), and the blue-sensitive cones are few and located away from the macula of the retina, again making it harder to spot the blue color of hot stars.
I don't expect, however, that there will be a lot of difference. [Shill time] Last march, our astronomy club flashed on and off two 800 watt search lights, along with my 1 watt blue laser (probably about 1/2 watt contrary to its rating) at the ISS where Don Pettit and Dan Burbank observed us from the cupola. They saw the tiny blue light as blue, especially when the search lights were blocked. [This was historic since, supposedly, no one had ever accomplished a light signal to any space venturer in the history of mankind.]
Yep, and I enjoyed those discussions in the yellow sun thread here.P.S. By the way, speaking of the color of the Sun, I am very well aware that it is intrinsically white. However, seen through the Earth's atmosphere, it gets reddened to a slightly yellowish color.