A modern day Earth nation is at war with another. That other nation is extremely advanced but they are also pacifists. Instead of killing peoples their gun rounds and shells have the effect of wormholes and teleport peoples to a distant planet 2000 light-years away as prisoners of war. The prisoners are returned after the war.

The solar system that planet is on contains 3 stars. The orbits of those suns insures that nights doesn't exist on that planet.

Question: Assuming the biological living conditions of the planet are otherwise the same as Earth. Besides the effect of having no nights, would there be any long-lasting effects on the visual systems or psychology of Earth human beings of being in such a setting for several months?

To make it easier to answer the question the 3 stars consists of a far-out luminous red giant, a star like the sun, and a compact faint blue star . The question assumes the planet is in the habitable zone of all three stars and that the star aren't flaring more than the Sun or causing more radiations than on Earth. The illumination of the individual colors from each sun varies but the global illumination (mix of red, yellow and blue light) is about always the same.

TL,DR: Would humans beings from Earth be seriously injured or killed from the long period variation of the main color a bunch of stars projects on a planet?

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    $\begingroup$ I'd like to point out the question isn't about the effects of a lack of day/nights cycle but about the effect of having a strong light which vary in color. For example I know it would kill plants because photosynthesis depends on the color of the sun. My question is wheter there would be deadly effects like that on humans $\endgroup$ – Mystra007 Nov 10 '14 at 23:48
  • $\begingroup$ Get your question now...can you define the 3-stars any further than 'continual daylight' so answers can address something beyond 'continual daylight'? $\endgroup$ – Twelfth Nov 10 '14 at 23:48
  • $\begingroup$ Could you edit the question to include the argument about color? The day/night cycle would dominate the question you asked, so mentioning color in the question would help focus us. Also, are there already edible plants on this planet, or do the POWs have to pack their own through the wormhole. $\endgroup$ – Cort Ammon Nov 10 '14 at 23:52
  • $\begingroup$ I've added a couple of elements to hopefully clear the issues. $\endgroup$ – Mystra007 Nov 10 '14 at 23:55
  • $\begingroup$ Understand that currently we don't really know why most mammals have only two types of color receptors, but mantis shrimp have eyes the would put Superman to shame, and everything in between. Or why spiders have five eyes, insects have thousand fused into two and eagles have only two. And all under the same sun. $\endgroup$ – RBarryYoung Nov 11 '14 at 4:30

To adequately answer this question, we need to know the spectral class of all of the stars in this system, however, the effects on humans of each of the spectral classes individually can be described:

Class O, B - blue stars. These stars have a very high UV output, as well as being very bright for their size. Humans exposed to their light would be quickly sunburned, and unlike our sun, just having such a sun in your field of view for more than a few seconds could cause temporary retinal afterimages. Longer exposure could cause blindness without sufficient protection.

Class A, F - white & yellow/white stars. These stars are not quite as bright, but they still produce more UV than our sun, though less than O and B stars. Sunburn would still be an issue, though blindness would not be much of an issue.

Class G - yellow stars. Just like our sun. We know what the effects of such a star are from personal experience.

Class K - orange stars. Not much UV at all. Dark skinned people could suffer from Vitamin D deficiencies if not provided in their diet even if they go about practically naked. Light skinned people might get enough UV to produce Vitamin D if they don't wear much clothing. Sunburn is not an issue.

Class M - red stars. No UV to speak of. Everyone has to gain Vitamin D from their diet, since they won't be able to produce it from UV exposure.

The effects of having several of these stars in the same system would be cumulative - blue stars could cause blindness and sunburn, but any UV-producing star would compensate for the lack of UV from orange and red stars.


Size doesn't matter, it is only the colour that matters. Blue stars produce most of their radiation in the UV part of the spectrum, and red stars produce most of their light in the IR part of the spectrum.

Given equal visible light luminosity, the red star would produce no UV, and thus sunbathing in its light would cause no sunburn regardless of the time spent in its light. This would be the warmest part of the day, given its high IR output.

The yellow star would produce enough UV to prevent vitamin D deficiencies, as would the blue star.

The blue star itself, while not producing more visible light in total, would concentrate its light into a smaller point in the sky, and would appear much brighter, easily causing retinal afterimages like looking at a welding arc. Also, it would cause sunburn quite quickly, in a matter of minutes. This would be the coolest part of the day due to the lower levels of IR.

Vitamin D deficiency would definitely not be a problem unless people hid from the blue and the yellow suns altogether.

Atmospheric ozone could mitigate UV exposure to some degree, but it is unlikely that such an effect would be much greater than that of our own ozone layer, and could well be less.

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  • $\begingroup$ Wouldn't the size of those stars matters as well? And the atmosphere of the planet? I'm pretty sure a star like the Sun is extremely dangerous without the right atmosphere and that a blue star would be tame with the right atmosphere. Or that a small blue star wouldn't matter much. Or are you saying that the visible light of a star is correlated with the UV it produces? $\endgroup$ – Mystra007 Nov 11 '14 at 0:09
  • $\begingroup$ @Mystra007 There aren't a lot of small blue stars. Most are massive supergiants, radiating a lot of energy. $\endgroup$ – HDE 226868 Nov 11 '14 at 0:11
  • $\begingroup$ A small blue star - a "blue dwarf" would be too cool to be a primary unless the planet was pushed very close to it. And then the UV might be almost as bad as for a supergiant. $\endgroup$ – Oldcat Nov 11 '14 at 0:56
  • $\begingroup$ Stars radiate energy in a similar curve. If the majority is in blue, the high end tail extends up into the UV range and a larger fraction of all light is in that range than a yellow or red star. $\endgroup$ – Oldcat Nov 11 '14 at 0:58
  • $\begingroup$ @Oldcat, Some higher-frequency EM energy from a blue star would be converted to IR in a planetary atmosphere making it still capable of warming a world, but I did make the point that UV would be appallingly high. $\endgroup$ – Monty Wild Nov 11 '14 at 1:02

TL,DR: TL,DR: Would humans beings from Earth be seriously injured or killed from the long period variation of the main color a bunch of stars projects on a planet?

My TL;DR: Yes.

Could such a scenario (referring to the planet being within the habitable zones of all three stars) exist? I'd think not. This arrangement would not be stable. Sure, multiple-star systems exist - and there have been systems discovered with up to 7 stars - but there's almost no way the planet could continue to be in the habitable zone of all three for more than a very short amount of time. In fact, I think it's likely that the system would consist of one star orbiting the other two, as is the case in Alpha Centauri.

But I guess I'll disregard that, although I think this is a valid point for the tag. I can elaborate on this if you want me to, but I can avoid it for now.

Back to the question:

TL,DR: Would humans beings from Earth be seriously injured or killed from the long period variation of the main color a bunch of stars projects on a planet?

I'll go with a sad yes here. It does depend on how far away from each of the stars the planet is, but I think that, given how large the stars are, that the output of radiation will be pretty huge. The Sun has a luminosity of 3.826 $\times$ 1024 Watts. Adding together the probable luminosities of these three stars, we get 518 solar luminosities (a red giant, e.g. Aldebaran) + 1 solar luminosity (a Sun-like star) + 91,000 solar luminosities (a blue star, e.g. Zeta Ophiuchi) $=$ 91,519 solar luminosities. That's pretty bright. It also means a lot of UV radiation, meaning that unless there's a thick ozone layer on the planet, these people are going to be pretty unhappy.

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  • $\begingroup$ It wouldn't have to be in the habitable zone of all three stars, 2 of the three just need to produce enough illumination to banish night. $\endgroup$ – Oldcat Nov 11 '14 at 0:24
  • $\begingroup$ @Oldcat Not necessarily. The planet could be hidden behind one of the stars, so only one half would be illuminated. And the question requires that it is in the habitable zone of all three. $\endgroup$ – HDE 226868 Nov 11 '14 at 0:26
  • $\begingroup$ @HDE226868 Yeah I didn't mean to write that but I did so I'll accept answers based on what I wrote since it's a bit too late based on the quality of the answers to change the bit about habitable zone. What I really meant was "the habitable zone of the system of 3 stars which are luminous enough to light the surface (which can basically mean just the habitable zone of one of them)" $\endgroup$ – Mystra007 Nov 11 '14 at 0:29
  • $\begingroup$ @Mystra007 Okay, I can modify my answer. $\endgroup$ – HDE 226868 Nov 11 '14 at 0:31
  • $\begingroup$ I picked Monty Wild answer because I thought it was generally the most informative. I wish I could have picked yours too, I had no idea blue stars were that deadly and that put a massive limit on the reality check part of the question. $\endgroup$ – Mystra007 Nov 11 '14 at 0:41

Humans are remarkably adaptive to colored light. We would generally be unaffected by the colors of the stars (though don't disregard the "no nights" thing... it'll be a doozie)

  • Our eyes/minds adapt to the colors of lighting. It is believed this is designed to help with tracking animals. A deer in the shade is "bluer" than a deer in the sun because it is lit by ambient sky rather than the sun itself. We don't even notice this because our brain accounts for it. There are really neat optical illusions which abuse this to make you think a piece of paper is one color, and then reveal that it was a different color, but had simply been illuminated with colored light.

  • We already talk about temperatures of lightbulbs when looking at color warmth. We think of blueish florescent as sterile and yellow incandescent bulbs as warm and inviting.

  • You would want to make sure one of the suns have the UV needed to produce Vitamin D, or something on the planet will need to provide it. We do rely on the sun and our diet for Vitamin D.

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Two kinds of issues here. Physical and Psychological.

On the Physical side, you can safely assume there will be no changes and no hurt (unless you allow for high UV radiations to cause cancer or low UV not enought to get vitamin D). Our eyes are quite adaptable. Evolution is much more slow than the scenario you pose.

On the Psychological side, on Earth near the Poles there are actually long daytime periods (not with a lot of sunlight, but real daytaime), and I do not see norwegians being unhappy during their summers. They just close the windows and sleep as usual.

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A real issue I see with this world is that three stars isn't enough to banish night perpetually...these stars must orbit each other.

So the planet orbits one star, the sunlike star. The other two need to be far enough away to avoid perturbing the orbit of the planet. If they are close to the sunlike star, they will not light up the night sky, so that's out. So instead they will have to be distant. In this case the dim star, if far out past Pluto will likely be 'just another star' and not light up the night. The Red Giant, even if it does light up the night when the planet is between the sun and the giant, will not do so a half year later when the planet is on the other side of the orbit. Any odd configuration you set up will change as the suns orbit each other, with some period of hundreds to thousands of years or less.

When Asimov wrote Nightfall, he had considerably more suns in his sky. Six or Eight, and probably even this many could not be put in a configuration that would banish night forever. Even in the story all but one star was clustered in one part of the sky, and then another planet eclipsed it.


An interesting thought is for the red sun and the yellow sun to be in orbits like the Sun and Jupiter and then have a dwarf star in the L4 and L5 points of that system. Then these 4 suns would be orbitally locked with respect to each other, 60 degrees before and behind the yellow sun in its orbit. I'm not sure this would totally banish night for good even so, but the suns would be in fixed relation as long as the orbits held.

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  • $\begingroup$ +1 for using the Lagrange points to get out of the stability mess. $\endgroup$ – HDE 226868 Nov 11 '14 at 1:02
  • $\begingroup$ Doesn't help the day night mess as much as I hoped for a good part of the year, thought. $\endgroup$ – Oldcat Nov 11 '14 at 1:16

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