Improving realism by removing stars

[Kagehiko 10]

If you guys check out photos from the Apollo missions or pretty much any video from NASA's youtube channel, there are no stars in the sky. But these were taken with cameras, can humans see stars in space? Well, turns out Neil Armstrong had an interview on BBC in 1970 and he stated that the he couldn't see anything in the sky (except earth). So, what's going on?

This happens simply because the light reflected from other celestial bodies (such as earth or the moon) is bright enough to force cameras to use fast shutter speeds, which means less light is captured by the camera's sensor and thus no stars in the sky. *Almost* the same thing also happens with the human eye (we don't have shutters in our eyes, lol), that's why we can't see stars during daylight.

But what about these photos from the ISS?

The reason for this is that there are no other bright bodies in the images, so the cameras (and our eyes) compensate for this by increasing exposure. Luckily, our eyes handle this much better than cameras, that's why we can go to concert and see perfectly everything around us, yet every single photo taken with a smartphone will look horrible (and may I remind you, the cameras that rovers use are no better than current smartphone cameras).

But there's also another variable here, if the moon was made of some material that absorbed most light from the sun, if you took a photo focusing on the sky, it would capture the faint light from stars, because there would be no other objects reflecting light, meaning you could take a photo with low shutter speeds and capture the faint light from stars and other celestial bodies.

So, my point is, stars are always visible on deimos and on the asteroid belt, which is pretty unrealistic. But to make this more realistic, we have to do research on the surface on deimos to see if it would reflect enough light so that stars are not visible during daylight. Currently, I think that the ingame deimos is bright enough to make stars not visible.

But taking a closer look at the Deimos' wikipedia page, it says that Deimos has an albedo (ammount of light reflect from the sun) similar to C and D type asteroids.

If you take a look at this, you can see that the Deimos' albedo is 0.065, and that is very, very low. Moon's albedo is 0.12! This means that Deimos reflects almost no sunlight.

So, what does this all mean? This means that during daytime, if the sun is in the frame, no stars are visible. If Deimos had an higher albedo, no stars would be visible during daylight, even when not looking directly at the sun.

But this also means that Deimos surface won't be visible, which for the sake of gameplay purposes, should be kept the way it is.

I know that this can be a problem to code, because if the probe has 2 cameras facing different directions (with one of them poiting at the sun) one camera would see stars while the other one wouldn't.

If the devs want to take a more realistic approach, they should make Deimos' surface significantly darker.

Now, I know that Deimos looks pretty bright in every single photo that can be found on the internet, hell, even curiosity captured a video of Phobos eclipsing Deimos! But every single photo taken from space or earth is overexposed, and Curiosity can see Deimos because of Deimos is a LOT closer than our moon (Deimos Apoapsis: 23470 Km, Moon Apoapsis: 405503 Km), Mars' atmosphere diffuses very little light, and once again, the photos are overexposed (no stars in the photos!).

Oh, also, what type is the asteroid depicted on the game? If it is a C or D type, the same effect should apply, but if it is any other type, then no stars would be visible on the "day side" of the asteroid.

TL;DR

Basically, my suggestion is to remove stars when looking directly at the sun in Deimos.

[dram 14]

Hi Kagehiko, thank you for the detailed analysis. As Take On Mars is also meant to be a game, certain things are overlooked, including this issue you mention with exposure. You will notice ingame that when you look towards the sun everything will get darker, this is how the HDR works in the game, and real cameras would not have this effect as they also take only photos, so the exposure setting would be configured prior to actually taking the picture.

That said, implementing what you mention - that is, to hide stars if you are looking towards the sun for individual cameras - is quite problematic in terms of coding at this point and does not warrant the effort that would be involved. Thank you for the suggestion nonetheless!