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To clarify on the title, K-type main-sequence stars--shortened as "orange dwarves"--are subjects of excitement for astronomers and astrobiologists.

Why?

  1. They emit enough radiation to provide a high-enough temperature to make water liquid but not high enough for solar radiation. (This would mean no auroras, but it also means no genes would be damaged by UV exposure.)
  2. They have a longer lifespan than G-type stars. (15-30 billion years compared to our sun's total of ten billion.) This means that life would be given more time to evolve.
  3. They are three to four times more common than G-type stars, making the search for Earth-like exoplanets hypothetically easier.
  4. Despite having 45-80% of a G-type star's mass, they can still be just as bright.

Now let's throw Earth into this scenario. It still orbits this orange sun at a distance of 93 million miles. To narrow the scenario even further, this question focuses on the emphasis that a star has on color.

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These photos are of the hours of the day, from dawn to dusk under a blue atmosphere and a yellow star. Now imagine Earth still having its blue atmosphere but the star now being orange instead of yellow. To the human eye, would this change the color of any part of the day in any way?

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  • $\begingroup$ I think you'd find this interesting: www.solstation.com/images/star3sky.jpg I'm not entirely sure what you're looking for though. Like the range of colors for the whole day? I think whether or not there are moons or how bright they are will affect this, and if you are looking for ranges, knowing the atmospheric composition of your planet would help guide answers in the right direction. This question is actually pretty close to being answerable; it just needs a bit more information $\endgroup$ – Pleiades Apr 17 '18 at 2:33
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    $\begingroup$ "Despite having 45-80% of a G-type star's mass, they can still be just as bright." No, they are less bright, your planet needs to be closer to compensate for this. $\endgroup$ – Vincent Apr 17 '18 at 3:26
  • $\begingroup$ @Vincent That's not what this article says: newscientist.com/article/… $\endgroup$ – JohnWDailey Apr 17 '18 at 3:42
  • $\begingroup$ @Pleiades One--I can't click on the link. Two--the first question is the right answer. $\endgroup$ – JohnWDailey Apr 17 '18 at 3:42
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    $\begingroup$ To the human eye your K-type star is still a blinding ball of white in the sky. The sky's color would really be defined by the atmosphere and weather. A human compatible world would seem likely to have a similar range of atmospheric colors as Earth does. $\endgroup$ – StephenG Apr 17 '18 at 4:32
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All colors would undergo a subtle change. On Earth, daytime color temperature is assumed to be 5500K or higher. For a smaller K-type star, everything would seem like it is illuminated by a "Cool White" (3500K – 4100K) light bulb. Not as yellowish as Incandescent/Soft White (2700K – 3000K) light, but still a very perceptible difference.

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  • $\begingroup$ I'm actually not sure it would be noticeable unless you could do a direct comparison switching back and forth between suns. Most people see a 4000K LED as bluish, but it's actually yellower than daylight which most people would call yellowish. Some of that's doubtless due to the blue sky, but I think it's mostly because our eyes are not designed to see absolute differences very well. $\endgroup$ – Mark Olson Apr 17 '18 at 17:44
  • $\begingroup$ People would totally adapt to it, no problem. However, color temperature can play real tricks with our eyes, and something like Black and blue or white and gold dress can happen. $\endgroup$ – Alexander Apr 17 '18 at 17:49
  • $\begingroup$ @Alexander While I don't doubt your answer, I can't imagine what it'd look like visually. $\endgroup$ – JohnWDailey Apr 27 '18 at 4:35
  • $\begingroup$ @JohnWDailey this is actually very easy. All colors will look like it's a couple of hours later in the afternoon (or earlier in the morning), with the sunset and sunrise being particularly reddish. $\endgroup$ – Alexander Apr 27 '18 at 6:55

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