How would the night sky look from the Martian surface?
Would there be more stars visible or fewer, compared with Earth?
Would they appear brighter, dimmer or the same?
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1$\begingroup$ I'd imagine that the night sky would look similar to that on earth at midnight in a remote place. Mars has an extremely thin atmosphere so sundown gives almost instant darkness. Also, there's almost no light pollution. I guess the biggest difference would be the other planets. $\endgroup$– Sumyrda - remember MonicaMar 23, 2015 at 5:46
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$\begingroup$ Would the thin atmosphere not cause more stars to be visible? Also what difference would exist in the other planets $\endgroup$– arahantMar 26, 2015 at 18:36
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$\begingroup$ Well, I don't know enough about these things to really answer your question, but today I found a software at www.stellarium.org which lets you choose a point on earth or mars or lots of locations and shows you the current sky including planets. You can even have it draw the planets path in the sky. $\endgroup$– Sumyrda - remember MonicaApr 18, 2015 at 19:40
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$\begingroup$ What light pollution would there be Sumyrda? Small villages of aliens? $\endgroup$– user6784Jun 11, 2015 at 14:40
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$\begingroup$ And sundown does not give instant darkness. There is so much dust in the air (and the atmosphere is so thick compared to the size of the planet) that twilight lasts 2 hours (the longer Mars hours?) compared to 90 minutes here on Earth. (both for middle latitudes when not in summer). There's a Wikipedia article for astronomy on Mars. $\endgroup$– user6784Jun 11, 2015 at 16:20
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I'll add to Wayfaring Stranger's comments. In fact most of the time you would be able to see fewer stars in the night sky of Mars, than in a good dark night sky on Earth, because of dust obscuration.
Even in favourable conditions, the optical depth of the Martian atmosphere is usally somewhere between 0.5 and 1 per airmass. (Petrova et al. 2012; Lemmon et al. 2014) and is nearly wavelength independent. This corresponds to a reduction in flux to between 37% and 60% of its value above the atmosphere. This compares to a typical optical (V-band) extinction of around 0.1 magnitude at a good site on Earth, which allows 90% of the flux through. There are times when it can be much worse than this on Mars.
This means that the limiting magnitude on Mars would be somewhere between 0.44 and 0.96 magnitudes brighter than it is on a dark site on Earth and that all the stars would be fainter by these values.
As a rough guide to the effect this has I took the Hipparcos catalogue and made a frequency histogram of V-magnitude of the stars. If we define a Hipparcos magnitude of 6 as the limit you can see from a good dark site on Earth, then you would see 4559 stars (that's over the whole of the sky in both hemispheres). If that limit was reduced to 5.56 or 5.04, then this number decreases to 2745 or 1560 respectively. Thus there would be a reduction in the number of stars you could see by typically between a factor of 1.66 and 2.92.
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$\begingroup$ I believe 0.33 extinction per airmass is about average for sea level of average humidity. 0.5 to 0.6 on a summer night in Nebraska. Is the East Coast summer worse? Maybe? I don't know if there's something special about the Plains climate or if that's just bad for a site that does science. Is the tropics worse? Probably. LA during a California-wide blackout and a poor air day? Must be. But yes, all in all Mars is usually worse. $\endgroup$– user6784Jun 11, 2015 at 14:50
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$\begingroup$ @user6784 What units? If that is magnitudes then it truly is appalling. I guess I've been spoiled by the sites I've observed at (which are near the tropics, but well above sea level). $\endgroup$– ProfRobJun 11, 2015 at 16:53
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$\begingroup$ V Magnitudes. Okay, the extra 0.1 or 0.05, 0.1 (I forgot) might've been cause Pinatubo wasn't completely dissipated yet, but according to astropix.com/HTML/L_STORY/SKYBRITE.HTM , 0.5 in summer is not unusual at all in humid low altitude climates. A cite for 0.33: lightpollution.it/cinzano/download/0108052.pdf I doubt the water vapor content ever gets low enough for it to exceed 0.2 here (East Coast of US, I just noticed that your use British spelling). $\endgroup$– user6784Jun 12, 2015 at 0:05
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$\begingroup$ (continued) So if you're not familiar, Los Angeles is famous here in the States for having brown nitrogen oxide smog for days or weeks at a time so it's close to the worst. Maybe a third world country's smog is the worst. $\endgroup$– user6784Jun 12, 2015 at 0:11
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