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The Sun looks yellow from Earth because we see it through the atmosphere; in space the Sun looks rather white. Do A-, B- and O-type stars look blue from both their planet's atmospheres and outer space? Do red dwarfs look reddish even if you look at them from space (I mean close to them, in their own planetary system)?

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    $\begingroup$ No, the Sun looks white when it's high in the sky. OTOH, it does transition through colours ranging from yellow, through orange, and red as it approaches the horizon. $\endgroup$
    – PM 2Ring
    Jun 11, 2021 at 9:50
  • $\begingroup$ @PM2Ring Yesterday I looked at the Sun in an attempt to recognize some part of it covered by the Moon. (dangerous, I know) It was around midday and the Sun looked yellow to me. During sunrise and -set it looks orange because you look through even more atmosphere. In space it looks more white, though on ProfRob's link it still seems rather yellow. It's just that it's so bright. $\endgroup$
    – John
    Jun 11, 2021 at 10:49
  • $\begingroup$ Ok, but please see physics.stackexchange.com/q/189217/123208 & the links therein. FWIW, I've (mostly) lived ~34°S latitude, so perhaps I'm used to the Sun having a fairly high altitude for most of the day. $\endgroup$
    – PM 2Ring
    Jun 11, 2021 at 12:21

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This site shows the colours that stars would have if their intrinsic spectra were viewed. The simulations do not have any intervening atmosphere and assume that the star is bright enough that the physiological effects that mean colour vision doesn't work at low light levels can be ignored.

What stars look like through the atmospheres of their own planets would be entirely dependent on the atmosphere those planets had.

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  • $\begingroup$ Interesting, thanks. I should add to this that the Sun has a G5V luminosity rather than G2V. In case of atmospheres we could have assumed an Earthlike pressure and composition. But I guess any star looks in a lower wavelength when seen through an Earthlike atmosphere. $\endgroup$
    – John
    Jun 11, 2021 at 8:01
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    $\begingroup$ @John spectral type is based on the appearance of the spectrum. Main sequence stars have a range of luminosities during their lives, even at the same spectral type. $\endgroup$
    – ProfRob
    Jun 11, 2021 at 8:29
  • $\begingroup$ @John The Sun's effective temperature is 5770 to 5780 kelvin, depending on which article one reads. (A typical value is 5778 K.) This is solidly in the G2V category. There are some questionable tables on Wikipedia that suggest the Sun is G4V. It isn't; those tables are wrong. Or as ProfRob put it, those tables are dodgy. There isn't a good American English equivalent to the British English "dodgy". "Questionable" comes close. In this case, dodgy is just about perfect, from my admittedly dodgy American English understanding of British English. $\endgroup$ Jun 11, 2021 at 13:36

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