<p>Your plots are incorrect in the segments of high pressure as well as of low star temperature. At high pressure the important factor becomes light extinction, which makes the sky yellowish unless there's really large spectral power density in blue region. At low star temperatures there's so low amount of blue light that the dependence of scattering cross section on wavelength isn't enough to compensate: the exponential factor in the Planck's law can't be beaten by the <span class="math-container">$\lambda^{-4}$</span> factor of Rayleigh scattering.</p>
<p>Also, at low pressure the extinction is much less pronounced than at normal pressure, so that even when the Sun is low, the atmosphere doesn't become yellow. This is especially easy to see when the star temperature is high: its blueness compensates the little yellowing that could happen, so we see it as whitening or lighter-bluing.</p>
<p>Still, I don't think one could easily guess it right, so you've actually done a good job. For the sake of completeness, below I'm including my results of numerical simulation of three atmospheres (air only, no aerosols, no ozone) lit by black-body stars with the same set of temperatures as used in your table. Simulations done by my (still WIP) software, <a href="https://github.com/10110111/CalcMySky" rel="nofollow noreferrer">CalcMySky</a>.</p>
<p>Sun elevation 85°.</p>
<div class="s-table-container">
<table class="s-table">
<thead>
<tr>
<th>Star temperature, K</th>
<th>Pressure 0.25 bar</th>
<th>Pressure 1 bar</th>
<th>Pressure 10 bar</th>
</tr>
</thead>
<tbody>
<tr>
<td>8500</td>
<td><a href="https://i.sstatic.net/jYPRj.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/jYPRj.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/99egU.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/99egU.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/Do7Xu.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Do7Xu.png" alt="" /></a></td>
</tr>
<tr>
<td>7400</td>
<td><a href="https://i.sstatic.net/1up5J.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/1up5J.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/A9LL4.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/A9LL4.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/FxnTv.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/FxnTv.png" alt="" /></a></td>
</tr>
<tr>
<td>6700</td>
<td><a href="https://i.sstatic.net/I0n9u.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/I0n9u.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/FIs4o.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/FIs4o.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/9pIDm.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/9pIDm.png" alt="" /></a></td>
</tr>
<tr>
<td>6040</td>
<td><a href="https://i.sstatic.net/QSQCy.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/QSQCy.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/8a5mv.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/8a5mv.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/6exbd.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/6exbd.png" alt="" /></a></td>
</tr>
<tr>
<td>5570</td>
<td><a href="https://i.sstatic.net/2JpuX.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/2JpuX.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/rYVcF.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/rYVcF.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/MRS2v.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/MRS2v.png" alt="" /></a></td>
</tr>
<tr>
<td>5100</td>
<td><a href="https://i.sstatic.net/PYVJy.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/PYVJy.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/idGx7.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/idGx7.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/Amt8k.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Amt8k.png" alt="" /></a></td>
</tr>
<tr>
<td>4350</td>
<td><a href="https://i.sstatic.net/tNlQT.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/tNlQT.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/IjUR6.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/IjUR6.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/m1yZm.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/m1yZm.png" alt="" /></a></td>
</tr>
<tr>
<td>3670</td>
<td><a href="https://i.sstatic.net/i9etz.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/i9etz.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/TUX3m.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TUX3m.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/uA93C.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/uA93C.png" alt="" /></a></td>
</tr>
<tr>
<td>2840</td>
<td><a href="https://i.sstatic.net/8LQ0K.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/8LQ0K.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/qCm06.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/qCm06.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/OSuOm.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/OSuOm.png" alt="" /></a></td>
</tr>
<tr>
<td>2000</td>
<td><a href="https://i.sstatic.net/bBcc1.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/bBcc1.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/6ckfs.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/6ckfs.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/oRkWM.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/oRkWM.png" alt="" /></a></td>
</tr>
</tbody>
</table>
</div>
<p>Sun elevation 5°.</p>
<div class="s-table-container">
<table class="s-table">
<thead>
<tr>
<th>Star temperature, K</th>
<th>Pressure 0.25 bar</th>
<th>Pressure 1 bar</th>
<th>Pressure 10 bar</th>
</tr>
</thead>
<tbody>
<tr>
<td>8500</td>
<td><a href="https://i.sstatic.net/7U3Qb.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/7U3Qb.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/gEMtG.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/gEMtG.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/V3ko7.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/V3ko7.png" alt="" /></a></td>
</tr>
<tr>
<td>7400</td>
<td><a href="https://i.sstatic.net/jk4jg.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/jk4jg.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/9bUkA.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/9bUkA.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/34L1P.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/34L1P.png" alt="" /></a></td>
</tr>
<tr>
<td>6700</td>
<td><a href="https://i.sstatic.net/8hiE4.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/8hiE4.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/yN954.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/yN954.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/YLcjM.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/YLcjM.png" alt="" /></a></td>
</tr>
<tr>
<td>6040</td>
<td><a href="https://i.sstatic.net/n1vFD.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/n1vFD.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/VOZqx.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/VOZqx.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/bnbnQ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/bnbnQ.png" alt="" /></a></td>
</tr>
<tr>
<td>5570</td>
<td><a href="https://i.sstatic.net/gYiGz.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/gYiGz.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/chIAz.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/chIAz.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/Bp2SG.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Bp2SG.png" alt="" /></a></td>
</tr>
<tr>
<td>5100</td>
<td><a href="https://i.sstatic.net/TTwrg.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TTwrg.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/QP8q4.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/QP8q4.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/euZNt.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/euZNt.png" alt="" /></a></td>
</tr>
<tr>
<td>4350</td>
<td><a href="https://i.sstatic.net/77nqm.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/77nqm.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/oPMaF.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/oPMaF.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/dTMPy.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dTMPy.png" alt="" /></a></td>
</tr>
<tr>
<td>3670</td>
<td><a href="https://i.sstatic.net/fETCn.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/fETCn.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/ke1eT.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ke1eT.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/Nve20.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Nve20.png" alt="" /></a></td>
</tr>
<tr>
<td>2840</td>
<td><a href="https://i.sstatic.net/cDelR.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/cDelR.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/EFD1B.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/EFD1B.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/wm6Fx.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/wm6Fx.png" alt="" /></a></td>
</tr>
<tr>
<td>2000</td>
<td><a href="https://i.sstatic.net/z6NHY.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/z6NHY.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/GZu6H.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GZu6H.png" alt="" /></a></td>
<td><a href="https://i.sstatic.net/e0Y4E.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/e0Y4E.png" alt="" /></a></td>
</tr>
</tbody>
</table>
</div>
CC BY-SA 4.0
2021-05-15T18:22:47.287Z
2021-05-15T18:22:47.287Z
Ruslan
<p><a href="https://i.sstatic.net/EirxR.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/EirxR.jpg" alt="enter image description here"></a>I think the star,its halo and cloud can't be darker than the sky color even early M type still look blindingly bright orange-red on the sky not dim orange-red.
The sky color, if heavier i think it will look more "desaturate"(brighter too <strong>but not bright to the point it's brighter than the star</strong>) and thecolor shift toward the red side(you are correct) <strong>that dense sky will be affected by the color of starlight very intensely to the point it's almost have the same color of the starlight</strong>
<strong>example:</strong> 10 bars sky on a planet around K5V sun would look light orange-ish grey also the cloud would look bright orange, same color for the star's halo.
<strong>example2:</strong> 10 bars sky on a planet around A5V sun would look bright pale teal/cyan with yellowish white cloud same color for the star's halo.
<strong>example3:</strong> 5 bars sky on a planet around A5V sun would look powder blue with pure white cloud, same color for the star and its halo.</p>

CC BY-SA 4.0
2020-03-28T15:26:07.907Z
2020-03-28T15:56:12.373Z
2020-03-28T15:56:12.373Z
Techodom Boonyasoma
<p>(Some of) These plots are incorrect. Whilst Rayleigh scattering has a steep dependence on wavelength <span class="math-container">$(\propto \lambda^{-4})$</span>, it cannot scatter what is not there. There is almost no blue light at all coming from stars with <span class="math-container">$T_{\rm eff} &lt; 3500$</span> K.</p>

<p>A detailed description of the problem with your calculations(?) is given <a href="https://astronomy.stackexchange.com/questions/34726/how-would-the-sky-look-if-earth-orbited-a-red-giant-at-a-safe-distance/35237#35237">here</a> with regard to a red giant illuminating the Earth's atmosphere; but the reasoning is precisely the same for an M-dwarf spectrum. A star (actually a brown dwarf) at 2000 K emits a negligible amount of visible light and what there is would be in the far red part of the spectrum.</p>

CC BY-SA 4.0
2020-03-28T16:40:39.497Z
2020-03-28T16:40:39.497Z
ProfRob
<p>In the Space Engine, I found a massive (6.6 Earth masses) oceanid, 2 Earths in diameter. It rotates around a white-yellow F8 star with a temperature of 5930 degrees Celsius.</p>
<p>Atmospheric pressure is huge! 146 atmospheres. It consists mainly of CO2 - 48.5% and water vapor - 45.8% and a small proportion of nitrogen - 5.4%</p>
<p>The color of this atmosphere is incredibly interesting to me, both in terms of planetary science. I want to ask if this color of the atmosphere is real at this pressure? And what can be this color of the atmosphere with other types of stars?</p>
<p>As you can see, at a star height of 60 degrees above the horizon, the sky looks yellowish, that is, at such a pressure, a yellow tint of color is best seen, and blue generally dissipates and is visible only at sunset, when the star has dropped to 5 degrees above the horizon.<a href="https://i.sstatic.net/gXeM0.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/gXeM0.jpg" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2023-03-01T21:47:45.717Z
At 146 Atmospheres, no light is getting to the ground at all.
ProfRob
CC BY-SA 4.0
2023-03-02T19:39:28.023Z
As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer).
Community
CC BY-SA 4.0
2023-03-04T10:27:00.520Z
Let's take Venus as an example. The planet has 93 atmospheres. Light from our Sun could, in principle, reach the surface of Venus if it had no dense clouds. I really want to understand the subject of planetary atmospheres. This is interesting!
Mikee
CC BY-SA 4.0
2023-03-01T11:37:11.540Z
2023-03-01T11:37:11.540Z
Mikee
<p><strong>I'm an artist (and science enthusiast) and I've been trying to find a comprehensive resource that would help me clearly identify likely sky colors (as perceived by human vision) for exoplanets that have atmospheres with a similar chemical composition to Earth.</strong> It's trickier than I expected. I've cobbled together several resources, and built what I hope is a decently accurate chart of apparent sun color along with sky color.</p>

<p><strong>UPDATE: I have revised this post and added a new, improved sky chart (below). Science references for sky chart: <a href="http://www.xenology.info/Xeno/5.4.2.htm" rel="noreferrer">Ref A</a>, <a href="http://homepages.wmich.edu/~korista/colors_of_the_sky-Bohren_Fraser.pdf" rel="noreferrer">Ref B</a></strong></p>

<p><a href="https://i.sstatic.net/slxc3.png" rel="noreferrer"><img src="https://i.sstatic.net/slxc3.png" alt="New Sky Chart"></a></p>

<p><strong>How accurate is my chart? Is this a fair representation of sky/sun on alien worlds with heavily Nitrogen/Oxygen atmospheres? In what ways could I improve it?</strong></p>

<p>The chart is not meant to account for things like dust, the look of the sky at sunrise/sunset, or other atmospheric effects. This is meant to be a boilerplate for the baseline look of the sky during the day. However if you'd like to comment on how the sky may change during things like sunset, or with effects like volcanism, I'm game!</p>

<p>Also, I'm more interested in relative color, than getting absolute color 100% right. The image was built in a vector program in RGB mode, so assuming your screen is calibrated in the standard way, we are probably seeing almost the same thing. </p>

<p>Here are the key ideas I've gleamed from my reading that I'm using to build this. I consider most of them tentatively held, and am very open to input:</p>

<ul>
<li>Earth-like atmospheres would tend to be light to dark blue at the zenith, due to the scattering of low-wavelength blue light. If the planet's sun was very hot, the sky would look a deeper blue, while cooler stars would give the sky a lighter blue to almost white look. When the sun gets to 3000k and below, the sky starts to take on an orange/brown tinge.</li>
<li>Like on earth, the horizon is the lightest in color and the zenith the deepest.</li>
<li>Denser atmospheres would appear brighter (more washed out) and the primary color in the spectrum more "pure" (I'm unsure what the term "pure" means exactly when it comes to optical perception...would it look whiter?). Likewise, thinner atmospheres would be less bright than earth's and the colors more "pure."</li>
<li>With increasing pressure the sky color at the zenith becomes increasingly yellow. In my image this means that an earth-like sky at 10x earth pressure would appear blueish/green near the zenith.</li>
<li>At lower temperatures I'm assuming the sun would appear tinged by the color listed under "star temperature." Otherwise you'll probably only see the star's color when it's near the horizon. </li>
<li>I'm assuming when you get down into K and M class suns, the surroundings on the planet would take on a progressively redder tinge due to the decreasing prevalence of blue wavelength light.</li>
<li>I suspect the gradient of color from horizon to zenith will be steeper/gentler in some atmospheres. I've guessed that the gradient would be more apparent on a high G world (on the right).</li>
</ul>

<p>References: 
<a href="http://homepages.wmich.edu/~korista/colors_of_the_sky-Bohren_Fraser.pdf" rel="noreferrer">Reference #1</a>
<a href="http://www.orionsarm.com/page/321" rel="noreferrer">Reference #2</a></p>

<p>Original Chart:</p>

<p><img src="https://i.sstatic.net/nIfgG.png" height="300"></p>

CC BY-SA 3.0
2017-12-19T12:18:41.017Z
It is a hard task as for here on Earth I see all types of blue in your chart. But internally your chart and the reasoning leading to it seems ok. Good job. Once I posted a Q with no success at all. Perhaps can I address you to that?   As an artist and a science passionate you might help me. ...
Alchimista
CC BY-SA 3.0
2017-12-20T07:27:12.263Z
I think your scattering is backwards.   The blue sky and yellow sun is due to scattering.   A thicker oxygen/nitrogen atmosphere should be bluer than a thinner one, not less blue.    A thicker atmosphere might also have more clouds, but that's also temperature dependent and I'm guessing clouds aren't part of your equation.   Nice effort, by the way.
userLTK
CC BY-SA 3.0
2017-12-20T14:06:52.700Z
This is a really interesting question! It might be interesting to "calibrate" using a known sky besides Earth's. To that end, I've just asked the question [Why would Mars' sky appear blue at dawn and dusk, but red during the middle of the day (reverse of Earth)?](https://space.stackexchange.com/q/24108/12102)
uhoh
CC BY-SA 3.0
2017-12-20T14:20:31.750Z
@userLTK this is a *denser* atmosphere (10 bar), not necessarily thicker. The substantially shorter mean distance between molecules may have an impact on the steepness of the Rayleigh scattering (though I'm not sure how) or other kinds of scattering may come in to play. The reference cited in the [OP's link](http://www.orionsarm.com/page/321) is *Atmospheric Optics*, C.F. Bohren
uhoh
CC BY-SA 3.0
2017-12-20T20:57:35.057Z
@Alchimista What's the question?
n_bandit
CC BY-SA 3.0
2017-12-20T21:00:33.607Z
@userLTK I've looked into this more, and I'm fairly confident that as atmospheric pressure goes up, the sky becomes more yellow. So at something like 5-10 bar, the sky might appear teal, and when you get to 40 bar the sky would appear a muted yellow. This happens because as pressure goes up, there is more atmosphere between you and the sun. This means the atmosphere has more molecules and other particles to scatter the short wavelengths of light, so much so that the blue starts to scatter beyond perception, and the wavelengths that reach you go from blue > teal > yellow > white (at zenith).
n_bandit
CC BY-SA 3.0
2017-12-20T21:05:39.510Z
@userLTK Yes. I agree with your word choice of "denser." There are apparently two types of scattering at play in the atmosphere: Rayleigh and Mei scattering. I've found two great sources that both seem to agree that as the atmosphere density increases brightness goes up, but purity of primary wavelength color goes down. So from a low bar environment to a very high bar environment the normal mid-day zenith color would be: deep blue > powder blue (earth at sea-level), > azure > teal > yellow > yellow/white > white.
n_bandit
CC BY-SA 3.0
2017-12-20T21:05:48.043Z
My latest references: References: http://www.xenology.info/Xeno/5.4.2.htm, http://homepages.wmich.edu/~korista/colors_of_the_sky-Bohren_Fraser.pdf
n_bandit
CC BY-SA 3.0
2017-12-20T21:20:23.220Z
You could be right (and FYI, discussion isn't encouraged here unless moved to chat), but I'm not an expert.    I'd assumed that more atmosphere = more blue light scattering = darker bluer sky with equal sun, but maybe too much scattering would decrease the blue.   Not my expertise.  (This is kind of a physics/optics question - physics board maybe?)
userLTK
CC BY-SA 3.0
2017-12-20T21:45:57.307Z
Probably it has been removed due to lack of interest.  In brief I claim that in a clear day morning light and afternoon light look very different. To me is so. Skip sun set to avoid complication.  Just before noon light is whiter and crispy . After noon is more yellow.  But it should be symmetrical under all geometrical parameters except eyes adaptation to light  or the fact that am is after night while pm is after am ;) Any idea why or I am the only one to see that?
Alchimista
CC BY-SA 3.0
2017-12-21T01:57:51.937Z
I have added an updated and improved chart.
n_bandit
CC BY-SA 3.0
2017-12-22T10:28:26.827Z
This question was cross-posted, and got an answer here: https://worldbuilding.stackexchange.com/questions/100411/terrestrial-exoplanet-skies-ive-built-a-visual-sky-chart-is-it-correct
J. Chomel
CC BY-SA 4.0
2018-08-25T02:07:46.787Z
First of all great work, looks very aesthetic. However I'm a bit confused on what you're looking for. I assume you're looking for accuracy, but how can you measure what it actually looks like? We don't really have planets that match all those conditions... How do we calculate the color?
MystaryPi
CC BY-SA 3.0
2018-02-03T12:14:40.037Z
As you said that you are interested in other atmospheres or diffusion regimes I have just now answered  to https://space.stackexchange.com/questions/24108/why-would-mars-sky-appear-blue-at-dawn-and-dusk-but-red-during-the-middle-of-t
Alchimista
CC BY-SA 3.0
2018-02-03T12:16:22.707Z
As well as to https://astronomy.stackexchange.com/questions/24804/do-the-gases-in-the-earths-atmosphere-affect-the-color-of-a-lunar-eclipse
Alchimista
CC BY-SA 3.0
2018-02-03T12:32:57.790Z
@n_bandit seems right . Higher pressure might depend on a geometrically thicker atmosphere or a higher g. In all cases, tough is incorrect to say that blue is scattered behind perception, shorter wavel. relative importance goes up. The tint of the dome should get progressively greenish yellow. The  limit in a very thick (in both senses) atmosphere is when all the star light is diffuse so the sky dome will be more white again.
Alchimista
CC BY-SA 3.0
2018-02-03T13:59:21.343Z
This can either help you or you can help him.  https://physics.stackexchange.com/q/267805/162193
Alchimista
<exoplanet><planetary-atmosphere><terrestrial-planets><weather><atmospheric-effects>
Terrestrial Exoplanet Skies – I've Built a Visual Sky Chart. Is it Accurate?
n_bandit
# Terrestrial Exoplanet Skies – I've Built a Visual Sky Chart. Is it Accurate?

(Asked by: username_0 on 2017-12-18)

**I'm an artist (and science enthusiast) and I've been trying to find a comprehensive resource that would help me clearly identify likely sky colors (as perceived by human vision) for exoplanets that have atmospheres with a similar chemical composition to Earth.** It's trickier than I expected. I've cobbled together several resources, and built what I hope is a decently accurate chart of apparent sun color along with sky color.

**UPDATE: I have revised this post and added a new, improved sky chart (below). Science references for sky chart: [Ref A](http://www.xenology.info/Xeno/5.4.2.htm), [Ref B](http://homepages.wmich.edu/~korista/colors_of_the_sky-Bohren_Fraser.pdf)**

[![New Sky Chart](https://i.sstatic.net/slxc3.png)](https://i.sstatic.net/slxc3.png)

**How accurate is my chart? Is this a fair representation of sky/sun on alien worlds with heavily Nitrogen/Oxygen atmospheres? In what ways could I improve it?**

The chart is not meant to account for things like dust, the look of the sky at sunrise/sunset, or other atmospheric effects. This is meant to be a boilerplate for the baseline look of the sky during the day. However if you'd like to comment on how the sky may change during things like sunset, or with effects like volcanism, I'm game!

Also, I'm more interested in relative color, than getting absolute color 100% right. The image was built in a vector program in RGB mode, so assuming your screen is calibrated in the standard way, we are probably seeing almost the same thing.

Here are the key ideas I've gleamed from my reading that I'm using to build this. I consider most of them tentatively held, and am very open to input:

* Earth-like atmospheres would tend to be light to dark blue at the zenith, due to the scattering of low-wavelength blue light. If the planet's sun was very hot, the sky would look a deeper blue, while cooler stars would give the sky a lighter blue to almost white look. When the sun gets to 3000k and below, the sky starts to take on an orange/brown tinge.
* Like on earth, the horizon is the lightest in color and the zenith the deepest.
* Denser atmospheres would appear brighter (more washed out) and the primary color in the spectrum more "pure" (I'm unsure what the term "pure" means exactly when it comes to optical perception...would it look whiter?). Likewise, thinner atmospheres would be less bright than earth's and the colors more "pure."
* With increasing pressure the sky color at the zenith becomes increasingly yellow. In my image this means that an earth-like sky at 10x earth pressure would appear blueish/green near the zenith.
* At lower temperatures I'm assuming the sun would appear tinged by the color listed under "star temperature." Otherwise you'll probably only see the star's color when it's near the horizon.
* I'm assuming when you get down into K and M class suns, the surroundings on the planet would take on a progressively redder tinge due to the decreasing prevalence of blue wavelength light.
* I suspect the gradient of color from horizon to zenith will be steeper/gentler in some atmospheres. I've guessed that the gradient would be more apparent on a high G world (on the right).

References:
[Reference #1](http://homepages.wmich.edu/~korista/colors_of_the_sky-Bohren_Fraser.pdf)
[Reference #2](http://www.orionsarm.com/page/321)

Original Chart:

![](https://i.sstatic.net/nIfgG.png)

**Tags:** exoplanet, planetary-atmosphere, terrestrial-planets, weather, atmospheric-effects

> **Comments:**
> **username_1**: It is a hard task as for here on Earth I see all types of blue in your chart. But internally your chart and the reasoning leading to it seems ok. Good job. Once I posted a Q with no success at all. Perhaps can I address you to that?   As an artist and a science passionate you might help me. ...  
> **username_2**: I think your scattering is backwards.   The blue sky and yellow sun is due to scattering.   A thicker oxygen/nitrogen atmosphere should be bluer than a thinner one, not less blue.    A thicker atmosphere might also have more clouds, but that's also temperature dependent and I'm guessing clouds aren't part of your equation.   Nice effort, by the way.  
> **username_3**: This is a really interesting question! It might be interesting to "calibrate" using a known sky besides Earth's. To that end, I've just asked the question [Why would Mars' sky appear blue at dawn and dusk, but red during the middle of the day (reverse of Earth)?](https://space.stackexchange.com/q/24108/12102)  
> **username_3**: @username_2 this is a *denser* atmosphere (10 bar), not necessarily thicker. The substantially shorter mean distance between molecules may have an impact on the steepness of the Rayleigh scattering (though I'm not sure how) or other kinds of scattering may come in to play. The reference cited in the [OP's link](http://www.orionsarm.com/page/321) is *Atmospheric Optics*, C.F. Bohren  
> **username_0**: @username_1 What's the question?  
> **username_0**: @username_2 I've looked into this more, and I'm fairly confident that as atmospheric pressure goes up, the sky becomes more yellow. So at something like 5-10 bar, the sky might appear teal, and when you get to 40 bar the sky would appear a muted yellow. This happens because as pressure goes up, there is more atmosphere between you and the sun. This means the atmosphere has more molecules and other particles to scatter the short wavelengths of light, so much so that the blue starts to scatter beyond perception, and the wavelengths that reach you go from blue > teal > yellow > white (at zenith).  
> **username_0**: @username_2 Yes. I agree with your word choice of "denser." There are apparently two types of scattering at play in the atmosphere: Rayleigh and Mei scattering. I've found two great sources that both seem to agree that as the atmosphere density increases brightness goes up, but purity of primary wavelength color goes down. So from a low bar environment to a very high bar environment the normal mid-day zenith color would be: deep blue > powder blue (earth at sea-level), > azure > teal > yellow > yellow/white > white.  
> **username_0**: My latest references: References: http://www.xenology.info/Xeno/5.4.2.htm, http://homepages.wmich.edu/~korista/colors_of_the_sky-Bohren_Fraser.pdf  
> **username_2**: You could be right (and FYI, discussion isn't encouraged here unless moved to chat), but I'm not an expert.    I'd assumed that more atmosphere = more blue light scattering = darker bluer sky with equal sun, but maybe too much scattering would decrease the blue.   Not my expertise.  (This is kind of a physics/optics question - physics board maybe?)  
> **username_1**: Probably it has been removed due to lack of interest.  In brief I claim that in a clear day morning light and afternoon light look very different. To me is so. Skip sun set to avoid complication.  Just before noon light is whiter and crispy . After noon is more yellow.  But it should be symmetrical under all geometrical parameters except eyes adaptation to light  or the fact that am is after night while pm is after am ;) Any idea why or I am the only one to see that?  
> **username_0**: I have added an updated and improved chart.  
> **username_4**: This question was cross-posted, and got an answer here: https://worldbuilding.stackexchange.com/questions/100411/terrestrial-exoplanet-skies-ive-built-a-visual-sky-chart-is-it-correct  
> **username_1**: As you said that you are interested in other atmospheres or diffusion regimes I have just now answered  to https://space.stackexchange.com/questions/24108/why-would-mars-sky-appear-blue-at-dawn-and-dusk-but-red-during-the-middle-of-t  
> **username_1**: As well as to https://astronomy.stackexchange.com/questions/24804/do-the-gases-in-the-earths-atmosphere-affect-the-color-of-a-lunar-eclipse  
> **username_1**: @username_0 seems right . Higher pressure might depend on a geometrically thicker atmosphere or a higher g. In all cases, tough is incorrect to say that blue is scattered behind perception, shorter wavel. relative importance goes up. The tint of the dome should get progressively greenish yellow. The  limit in a very thick (in both senses) atmosphere is when all the star light is diffuse so the sky dome will be more white again.  
> **username_1**: This can either help you or you can help him.  https://physics.stackexchange.com/q/267805/162193  
> **username_5**: First of all great work, looks very aesthetic. However I'm a bit confused on what you're looking for. I assume you're looking for accuracy, but how can you measure what it actually looks like? We don't really have planets that match all those conditions... How do we calculate the color?  

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## 4 answers

### Answer by username_6 on 2021-05-15. Score: 4

Your plots are incorrect in the segments of high pressure as well as of low star temperature. At high pressure the important factor becomes light extinction, which makes the sky yellowish unless there's really large spectral power density in blue region. At low star temperatures there's so low amount of blue light that the dependence of scattering cross section on wavelength isn't enough to compensate: the exponential factor in the Planck's law can't be beaten by the $\lambda^{-4}$ factor of Rayleigh scattering.

Also, at low pressure the extinction is much less pronounced than at normal pressure, so that even when the Sun is low, the atmosphere doesn't become yellow. This is especially easy to see when the star temperature is high: its blueness compensates the little yellowing that could happen, so we see it as whitening or lighter-bluing.

Still, I don't think one could easily guess it right, so you've actually done a good job. For the sake of completeness, below I'm including my results of numerical simulation of three atmospheres (air only, no aerosols, no ozone) lit by black-body stars with the same set of temperatures as used in your table. Simulations done by my (still WIP) software, [CalcMySky](https://github.com/10110111/CalcMySky).

Sun elevation 85°.

| Star temperature, K | Pressure 0.25 bar | Pressure 1 bar | Pressure 10 bar |
| --- | --- | --- | --- |
| 8500 |  |  |  |
| 7400 |  |  |  |
| 6700 |  |  |  |
| 6040 |  |  |  |
| 5570 |  |  |  |
| 5100 |  |  |  |
| 4350 |  |  |  |
| 3670 |  |  |  |
| 2840 |  |  |  |
| 2000 |  |  |  |

Sun elevation 5°.

| Star temperature, K | Pressure 0.25 bar | Pressure 1 bar | Pressure 10 bar |
| --- | --- | --- | --- |
| 8500 |  |  |  |
| 7400 |  |  |  |
| 6700 |  |  |  |
| 6040 |  |  |  |
| 5570 |  |  |  |
| 5100 |  |  |  |
| 4350 |  |  |  |
| 3670 |  |  |  |
| 2840 |  |  |  |
| 2000 |  |  |  |


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### Answer by username_7 on 2020-03-28. Score: 4

[![enter image description here](https://i.sstatic.net/EirxR.jpg)](https://i.sstatic.net/EirxR.jpg)I think the star,its halo and cloud can't be darker than the sky color even early M type still look blindingly bright orange-red on the sky not dim orange-red.
The sky color, if heavier i think it will look more "desaturate"(brighter too **but not bright to the point it's brighter than the star**) and thecolor shift toward the red side(you are correct) **that dense sky will be affected by the color of starlight very intensely to the point it's almost have the same color of the starlight**
**example:** 10 bars sky on a planet around K5V sun would look light orange-ish grey also the cloud would look bright orange, same color for the star's halo.
**example2:** 10 bars sky on a planet around A5V sun would look bright pale teal/cyan with yellowish white cloud same color for the star's halo.
**example3:** 5 bars sky on a planet around A5V sun would look powder blue with pure white cloud, same color for the star and its halo.


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### Answer by username_8 on 2020-03-28. Score: 2

(Some of) These plots are incorrect. Whilst Rayleigh scattering has a steep dependence on wavelength $(\propto \lambda^{-4})$, it cannot scatter what is not there. There is almost no blue light at all coming from stars with $T\_{\rm eff} < 3500$ K.

A detailed description of the problem with your calculations(?) is given [here](https://astronomy.stackexchange.com/questions/34726/how-would-the-sky-look-if-earth-orbited-a-red-giant-at-a-safe-distance/35237#35237) with regard to a red giant illuminating the Earth's atmosphere; but the reasoning is precisely the same for an M-dwarf spectrum. A star (actually a brown dwarf) at 2000 K emits a negligible amount of visible light and what there is would be in the far red part of the spectrum.


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### Answer by username_9 on 2023-03-01. Score: 1

In the Space Engine, I found a massive (6.6 Earth masses) oceanid, 2 Earths in diameter. It rotates around a white-yellow F8 star with a temperature of 5930 degrees Celsius.

Atmospheric pressure is huge! 146 atmospheres. It consists mainly of CO2 - 48.5% and water vapor - 45.8% and a small proportion of nitrogen - 5.4%

The color of this atmosphere is incredibly interesting to me, both in terms of planetary science. I want to ask if this color of the atmosphere is real at this pressure? And what can be this color of the atmosphere with other types of stars?

As you can see, at a star height of 60 degrees above the horizon, the sky looks yellowish, that is, at such a pressure, a yellow tint of color is best seen, and blue generally dissipates and is visible only at sunset, when the star has dropped to 5 degrees above the horizon.[![enter image description here](https://i.sstatic.net/gXeM0.jpg)](https://i.sstatic.net/gXeM0.jpg)

> **Comments:**
> **username_8**: At 146 Atmospheres, no light is getting to the ground at all.  
> **username_10**: As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer).  
> **username_9**: Let's take Venus as an example. The planet has 93 atmospheres. Light from our Sun could, in principle, reach the surface of Venus if it had no dense clouds. I really want to understand the subject of planetary atmospheres. This is interesting!  

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