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Comment by twmb | Hacker News Reader

I wonder if it's a planet such that the surrounding stars' lights prevent any other starlight from being seen, except for once every few thousand years.

One could only imagine a civilization that lives here and what would happen to society whenever the full night sky is occasionally seen...

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I know that you're being fatuous but in case anyone doesn't get the reference, check out Nightfall by Asimov - it's a classic sci-fi short story.

http://www.uni.edu/morgans/astro/course/nightfall.pdf

The planet is a Neptune-like gas giant, so no civilization there. It probably has big moons though, and with all the suns around they might be warm enough to develop life. I haven't done the math, but I'm guessing that when the moon is on the night side of the planet relative to the nearby stars, the location of the distant stars would cycle in basically the same way Jupiter does in our sky. It moves slowly relative to the background stars, but still rises and sets every day.

I don't know the details and couldn't do the math if I did, but I'm guessing those stars at 1000AU can't be much brighter than our full moon is, maybe combined with the light pollution of a big city. I've lived outside of New York all my life, and my night sky still has stars in it. Not many, but enough to know they're there, and sometimes on a clear night I can see quite a few.

> I'm guessing those stars at 1000AU can't be much brighter than our full moon is

They may well be fainter. According to Wikipedia, the Sun is about 400,000 times as bright as the full moon, on average:

http://en.wikipedia.org/wiki/Apparent_magnitude

So if the Sun were 1,000 AU away from us instead of 1 AU, it would be a million times fainter (1,000 squared), or less bright than the full moon.

But there are two of them, so that would mean closer to the moon's brightness, right? If I'm following, the sun would be about 40% as bright ast he full moon at 1000AU, so with the second start being smaller than, it may be 60%?

(Mock my math if need be, I'm not really trying here. :)

Yes, the second star would add to the brightness and make things closer. Also, I didn't see in the article what the actual brightnesses of the two stars 1,000 AU away are relative to the brightness of the Sun. I just used the Sun because it was easy to look up the relative brightness of the Sun vs. the Moon. :-)

Edit: I see from looking at more recent posts that the two distant stars are thought to be spectral class G and M. The Sun is a G, so it should be about the same brightness as the brighter of the two.

The planet is a Neptune-like gas giant, so no civilization there.

The gas creatures beg to differ.

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