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So I'm working on a world that orbits a blue star that's not much bigger (or even smaller) than the sun. I was thinking that an A-type star would be a good choice for it, but it's still is closer to white than blue. Is there any way for the conditions of an A-type star to be just right to give it a bright blue glow?

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    $\begingroup$ I don't understand. An A-type star is, by definition, white. If it were blue, it would be O-type. $\endgroup$
    – James K
    Commented Jan 7, 2017 at 17:37
  • $\begingroup$ Did you describe the reason for the bounty correctly? I would have thought that you still wanted a usable story idea and none suitable were suggested. But “more detail?” It appears the answers are already quite detailed and specific on the reasons for star color. $\endgroup$
    – JDługosz
    Commented Jan 11, 2017 at 8:09

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Here are your color options:

enter image description here


If you can get your star past infinite temperature, then you can have it be a nice blue rather than blue-white. A more feasible option is to make the star appear blue due to the atmospheric composition. Or, if something else needs to budge, you'll need to make it the largest type A you can (about 2.6 solar masses) and it'll be just between blue-white and deep-blue-white

But, basically, a bluish-whitish is the most likely outcome. For a human observer, at least.

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I see one serious problem - time scale.

enter image description here

Solution I - you use high concentration of handwavium to explain why it was possible to form planet and interesting enough life on such planet so fast. As an excuse I could imagine UV light splitting water, causing hydrged to escape and oxygen to accumulate, thus speeding up local great oxygenation even that allowed multicelluar life.

Solution II - blue dwarf - just wait The only problem that the universe is clearly to young for them and they are just predicted late phase of small red dwarfs. If your story can wait so much... Then you may use it. http://beyondearthlyskies.blogspot.be/2013/09/blue-dwarfs-stars-yet-to-be.html

Solution III - blue dwarf - lucky coincidence After a series of nearby supernovas (? not 100% sure how to get such composition, it may also involve serious amount of handwavium) a tiny star was formed with ultra high helium concentration, hundred of billion of years before their time, looking more or less like a blue dwarf.

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  • $\begingroup$ If there were precursors, they could have seeded and terraformed the planet. $\endgroup$
    – ifly6
    Commented Dec 29, 2016 at 15:15
  • $\begingroup$ That's kind of the tricky part, the story takes place within the near future, roughly a few decades from now. Plus the system is much younger than our own, so a blue dwarf is probably out of the question. $\endgroup$
    – Mattias
    Commented Jan 3, 2017 at 20:12
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The light given off by a blackbody spectrum at high temperatures like those found in stars, once you get above the temperature of the Sun's photosphere, which is around 5700 K, is going to be practically indistinguishable from white.

The first thing I thought of when it comes to this is absorbing the light coming off from the star. But any amount of dust between the star and the planet would get blown away over the course of a few thousand years.

I'm thinking you want something like this though.

Pleiades, Wikipedia

The rings around the stars are actually optical defects, so I'll ignore that. But the thing which makes the entire area blue is not anything to do with the stars. Rather, it has to do with the dust which reflecting the blue light coming off from the star itself.

This, due to radiation pressure from the star, cannot last for long, but like the Pleiades, the stars could be travelling through a particularly dusty region of the galaxy which provides the dust necessary to explain such scattering.

Secondarily, one should also note that this solution wouldn't make the star blue (it would still be blue-white). But rather, it would make, for a planet inside the cluster, the entire sky have a faint blue glow.

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  • $\begingroup$ What if the star itself contains impurities with the right absorbtion spectrum? $\endgroup$
    – ikrase
    Commented Dec 29, 2016 at 20:35
  • $\begingroup$ Such impurities already exist. If we look at the spectra of large stars, the emission lines are generally overpowered by the sheer heat of the plasma's continuous spectrum. Also, absorption spectra only exist when there is a hotter source behind some cooler gas. Such cooler gas would generally be removed from the system over a short timescale if it is close to the star. $\endgroup$
    – ifly6
    Commented Dec 29, 2016 at 20:37
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    $\begingroup$ That's a false color image. Here is another photo of the Pleiades in visible light. It demonstrates the actual blue-white color of the stars. $\endgroup$
    – Samuel
    Commented Jan 9, 2017 at 17:56
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If the sky were red rather than blue, might our sun look blue by physiological or neural colour-contrast effects? I'm not sure.

Anyway you can't get a red sky by scattering off dust because short wavelengths scatter more strongly than long. Hence blue sky. But suppose plants on this planet had evolved hydrogen bladders, and a different photosynthesis to Earth that worked on blue and green but not red? Then plant life would be red not green, and because of airborne plants the sky would also be reddish.

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Your A-type star has a Dyson Swarm of unknown (or known) origin around it. Except the modules are not entirely opaque, but almost transparent, and of a nice shade of blue.

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