New screenshot! The star field looks really nice:)
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Oh man, I wish I knew what we were looking at here. Whatâs causing the reddening near the horizon? It doesnât appear to be light from the sun reddened due to passing through the planetâs atmosphere falling on the ring. Maybe itâs light reflected off the ring reddened by the planetâs atmosphere as it makes its way to the camera? Whatâs that hazy band that runs parallel to the rings? The galaxy? An outer diffuse ring? My moneyâs on the galaxy, but itâs so hard to tell whatâs going on from a single still image.
The pic was posted on flavienâs twitter page. He mentioned that the Milky way was a work in progress, so Iâm guessing thatâs the parallel band. As the ring is only red towards the horizon, I believe your assumption of it becoming red as it traverses the atmosphere to the camera would be the most logical (sunrise/sunset distortionsâŚ)
I think itâs the color of the atmosphere at dusk bleeding onto the rings. You can see it in the planetary rings video if you look at the boundary between night and day on the planet. The terrain has a reddish hue at the boundary to show off a nice red sunset. I think the intended effect is this https://www.youtube.com/watch?v=a6a69dMLb_k&list=UUNEHBrhTUN4P_ZxIy29DNQw#t=324, but clearly it is also visible from space.
Itâs the background light getting scattered through the atmosphere. Itâs actually called âextinctionâ and is basically the same thing that causes day light to get yellowed by the time it reaches the ground, or the sun reddening at dawn.
Nope, although Iâd like to experiment with a bounce of lighting due to the ring getting lit thanks to IBL ( image based lighting ). But our IBL is very experimental atm. Since that pic was taken from the night side of the planet, it is currently entirely black; but with IBL, some light would get reflected from the ring and the terrain would be indirectly lit. I hope weâll have time to do it for the KS 
Yeah itâs the Milky Way, but as I explained on twitter itâs just a basic effect; it lacks the dust and additional effects it had a couple years ago when I had originally implemented it.
At some point I want to do a timelapse of this. Itâs actually looking pretty cool seeing it change at various times of the day
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When the community reads your side of the story it gives us that nostalgia weâve come to know over the years. I get a feeling of excitement each time I click on a post of yours. You guys really are a cool group of people.
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So, is that just a filter youâre using to simulate extinction, or are you actually calculating optical depths using extinction coefficients? I know youâve spent a ton of time working on Rayleigh scattering for your atmospheres over the years, so I know you must have been calculating optical depths or mean-free-paths using some reasonably realistic scattering cross-sections for that, so is the reddening just an extension of that in-engine?
Ring-shine would be super awesome cool. How far beyond that do you think you could go? Would planet-shine (e.g. Earth-shine) be realistically possible?
We are doing the actual calculations for extinction, in-scattering, etc.
Itâs definitely possible however there are a number of challenges for us to overcome. One of the big ones is that atmosphere is expensive and any sort of indirect illumination calculation involves approximated ray-tracing of some sort and that involves multiple executions of our atmosphere code. Another issue is shadows which are a never-ending source of frustration.
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I probably shouldnât be as excited about that as I am. I mean, the atmospheres have always looked great, but Iâve never considered the possibility that we would see the effects of reddening from space due to the planetary atmospheres.
Does this mean that total lunar eclipses will result in the red moon effect? Because I had been assuming no, but now I canât help but assume that they will (which would, in all honesty, excite me more than any kind of ship or weapon you could ever put in game).
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Yes we can do proper lunar eclipses. Theyâre particularly interesting when we use atmosphereâs that arenât blue and you get to see what crazy colors their sunsets look like. For an extra level of variation that obviously also depends on the color of the nearest star(s).
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I can almost hear Kichaeâs squee from here! 
If they start talking about specific opacities and wavelength dependent cross sections, youâll be able to hear me squee from Mars (mind you, I canât see that happening, as itâs computationally expensive with no benefit to the game other than introducing spectral absorption lines, but a guy can dream).
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Yeah, I canât see myself getting to Mars before they make a decision one way or another about this, either.
Still, computational costs can be optimized, the real question is whether or not itâd be faster, in terms of man-hours, to use this. If thereâs a set of equations, and probably a python lib, that gives as accurate looking a result as it is possible for science to measure, then using it might be faster than building an approximation from the ground up (with all the iterations itâll require to look good enough).
Probably not, though. I mean, unless the materials system happens to contain the data that those aforementioned equations need there could be quite a bit of data entry involved.
Iâm fairly certain older libraries of cross-section data are readily available, so if they wanted to do the calculations themselves, they could. Again, though, I donât think it really adds anything. Especially since you can fake the lines using readily available line lists (which are computed using the above mentioned cross-section data) and simply superimposing the lines on the atmosphereâs spectral energy distribution. Atmospheric composition data is already required for the engine to do the proper scattering calculations, and composition data is all thatâs needed to calculate line weights.
@INovaeKeith, @INovaeFlavien, out of curiosity are you using the same atmosphere code for stellar atmospheres, too? The global atmospheric physics is a little different in atmospheres due to the high percentage of excited and/or ionized atoms (depending on the starâs temperature), but scattering is basically the same. In fact, due to the exceptionally high concentrations of hydrogen and helium, scattering in stellar atmospheres is, generally, simpler than it is in planetary atmospheres (in fact, the majority of the scattering is due to Thompson scattering off of free electrons, and simple stellar atmosphere models neglect scattering off of everything but those electrons). Where it would get really interesting, though, is in very cool stars which tend to have a lot of neutral atoms, molecules, and even dust in their atmospheres, leading to increased reddening.
Our calculation is of course an approximation thatâs based on earthâs atmospheric composition which is primarily represented by Rayleigh and Mie scattering. While we can change the wavelengths of light and the relative density of aerosols, as well as the density distribution of the atmosphere itself, we cannot represent the various unique properties of different gasses on the atomic level other than to say they reflect X wavelengths of light instead of Y wavelengths.
Dusty stars would also undergo Rayleigh and Mie scattering (in addition to more complicated extinction events, such as bound-bound atomic and bound-bound molecular absorption/emission), which is why they appear redder than we would expect. The corollary to that is that from within those atmospheres, there would be something approximating a blue or violet sky. So, I mean, thereâs some of the exact same stuff going on. Just throwing that out there.
Since INovae takes aerosol concentrations into account when calculating scattering, and planetary atmosphere colours sound like theyâre computed dynamically, does that mean that the colour of that pink-purple gas giant we see in the rings video is computed based on composition? Or did you guys choose that?
The purple gas giant in the rings video is computed by saying itâs rayleigh scattering primarily scatters along purplish wavelengths. We then specify the density of aerosols, the thickness of the atmosphere, and the density distribution of the atmosphere. All of those parameters are plugged into a long series of equations that end with the purple pixels you see in the video =)
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Yeah, alright, here comes the squee.
Purpleâs an interesting colour to get from a scattering reaction, since purple light doesnât exist (and donât even get me started on all of the wise guys asking âwhy is the sky blue and not purpleâ; they thing they have a âgotchaâ, and then conflate the colours purple and violet). You need a combination of high frequency and low frequency visible light in order to create purple. This suggests weâre either looking at a system with an abundance of red light (which hasnât been evident to date), or that thereâs something in the giant planetâs atmosphere that is preferentially scattering red light. Thatâs really difficult to do with Rayleigh scattering due to the 1/wavelength4 dependence. Thereâs only a very small range of particle sizes over which the Rayleigh approximation holds for red light but not higher frequency light, and at those particle sizes the other frequencies should experience Mie scattering anyway, creating a grey or white smog (as all colours of visible light are being scattered).
Itâs interesting to note that the terminator on the purple world has a distinctly yellow/brown colour to it, almost as if it is a combination of orange, yellow, and green light. The sunset skies on that world have seemingly had most of the blue and red light filtered out of them, leaving sunsets that look the colour of thick, dense smog. The absence of blue and violet light can be explained with simple Rayleigh scattering (since it predominantly affects the blue end of the spectrum), but it takes something fairly special to scatter only red light.
Iâm more than curious, now, and I canât wait to get my hands on that purple planet.
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So, what are the devs working on now? The kickstarter video?
Yes, the Kickstarter video.
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