# How bright is the Martian landscape during the long (up to two hour) twilight?

The answer to the question "How much more quickly does night come on Mars compared to Earth? Will it be easier to see Mercury there?" says Martian twilight can last up to two hours.

Has any lander studied how bright the Martian landscape generally gets during any time of twilight? Is there a way of comparing the Martian landscape brightness to the brightness of the different phases of the moon on a cloudless night on Earth? Graph below is in foot-candles.

• It's a good question. As for the two hours of twilight, it remains to be seen just how bright that twilight actually is.
– uhoh
Mar 20, 2020 at 2:48
• I've asked the different but complementary question How bright is twilight on Mars compared to Earth?. However if an answer here can answer both we can close my new question as duplicate.
– uhoh
Mar 20, 2020 at 3:01
• perhaps a description about how twilight varies on earth to show the sort of thing you're interested on Mars? You might need to expand this question to demonstrate how it isn't a duplicate of uhoh's newer but clearer question
– user20636
Mar 27, 2020 at 8:49
• ¨ Has any lander studied how bright " , what exactly do you mean with that ? Could it be just taking images of the same spot during and after (or before) a twilight ? Mar 29, 2020 at 16:11
• well Cornelisinspace i think just based on pictures we can see that its not to far off from night, combined with my calculations it seems right but i guess my answer is more of an educated guess than a solid answer Mar 31, 2020 at 14:09

ok so with a quick search since mars gets 44% of the light on earth. so with some math we get about 1.5 lx but wait, mars's atmosphere is different than earth's we can assume mars's twilight is around 1 lx or at least less than 1.5 lx. Now keep in mind this is using civil twilight measurements. This is as far as I can go to answering but I think it's safe to assume its <1 lx. math: 3.4 lx*44%=1.54 lx

But wait there's more. Here I'm including some more math that might not make sense. so because 0.00001 of light is scattered per meter at atmospheric pressure. blah blah blah, there is only 0.00108 of the light that gets scattered... safe to assume twilight is very dark after all. and that's a generous number, very generous.

in conclusion mars twilight is very dark. the first answer has math that definitely works but doesn't take into account the atmosphere, the second takes care of the atmosphere but the answer I get seems off. the answer when combined is 0.003 lx + moonlight so I'll say an even (maybe a bit more) 0.01 lx to 0.02 lx, still very dim. (take into account that this is an approximation) but the image here shows it is similar to night time which makes sense. source

edit: taking into account dust we can assume this number is higher, but not by much because i cant calculate how exactly it would be, i can give a educated guess of <0.5 lx but >0.1 lx but i assume this number would change over time with weather.

https://en.wikipedia.org/wiki/Lux

https://en.wikipedia.org/wiki/Rayleigh_scattering

• Does this take into account that the Martian twilight "glow remains visible, but increasingly fainter, for up to two hours before sunrise or after sunset. The long martian twilight (compared to Earth's) is caused by sunlight scattered around to the night side of the planet by abundant high altitude dust," as part of the calculation? mars.nasa.gov/resources/5300/a-martian-sunset Mar 31, 2020 at 1:20
• hmm, no i didn't take that into account but from what i gained i calculated for scattering by air molecules so all id need to do is increase that number to cover for the dust, but im not sure how reflective the dust is. I essentially calculated for 108 meters of earth air but with the dust in play id have to im not sure. let me see what i can do Mar 31, 2020 at 1:53
• how is it now? i changed it a bit Mar 31, 2020 at 2:31