In my previous question, I asked about how close can two stars in a binary system be for planets around them to stay earthlike, assuming that both stars have very sunlike and both planets very earthlike parametres. After receiving lots of helpful answers, the distance I decided to go for was tiny bit over 20 AU distance, between the two sunlike stars.

But here my new problem comes - with the second star so close, how would my planets nights be affected?

With the distance of 18-22 AU (the distance fluctuates little as the two sun-like stars orbit around the centre of the mass of the two) between the two stars, every year for at least 5 months, night sky would be dominated by the second star, brightness of which would be only 300-450 times lower than the Sun, thousand times brighter compared to the brightness of a full moon which is 400 000 times lower than Sun.

I can understand that concept mathematically, but physically, I honestly can't even imagine how would this kind of bright night look like. I know that it would be as bright as the Sun looks from the Uranus (haha), but I've never been on any of the moons of Uranus, so I can't compare. Just what would that mean for people and animals living on my planet? How can I understand what would it look like, so that I can build my worlds around it?

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    $\begingroup$ Maybe this might help. Obviously, it's not solid science so. brightside.me/wonder-curiosities/… $\endgroup$ – Sach Dec 12 '19 at 23:03
  • $\begingroup$ Tbh, I'm not looking for solid science but just for a way to visualize it and understand its implications. $\endgroup$ – Failus Maximus Dec 12 '19 at 23:09

At 20 AU, Sun-like star will produce 20*20 = 400 times smaller illumination.

Based on this data: Lux, illumination will be in the range of 200-300 lux (with clear skies), which is more than on Earth on a "Very dark overcast day", but less than "Sunrise or sunset on a clear day" - more in line with well-lit building interiors.

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  • $\begingroup$ Yeah, that's a very good way to turn those numbers into something I know. Although, I'll also have to take in account that weather is still a thing at night(it can be overcast), so the range is wider than just 200-300. $\endgroup$ – Failus Maximus Dec 12 '19 at 23:21
  • $\begingroup$ @Failus Maximus you are welcome, but I'd like to let you know that it is a usual policy to wait for 24 hours before accepting an answer, because users from all time zones might want to get their chance. $\endgroup$ – Alexander Dec 12 '19 at 23:24
  • $\begingroup$ OK, sorry, didn't know that. $\endgroup$ – Failus Maximus Dec 12 '19 at 23:25

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