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Recently, I tried to read Asimov's Nightfall, which is about a planet with six suns in the system. Then the suns all set at a close interval, which hasn't happened in their recent history, and top scientists are envisioning mass panic.

It got me thinking, how can a planet be affected by multiple suns?

Tatooine from Star Wars has two suns. To my understanding, those two orbit one another with the planet orbiting around the common focus of the duel stars. Both suns affect Tatooine, but the planet is the exact distance to survive. Neither sun absorbs or has the planet ricochet away because the focus is on the center point, not the suns.
(VV below is a lazy model.)


Six suns would have a very complex orbit if they orbited one another. The novella suggests that the suns are not in a common orbit though. I can't see that many stars having a mutual system, never mind planets in that system.

I really have no idea how a six star system would work. Asimov was a very intelligent man, so it's probably not just hoopla; he probably had some idea of how it would work. An explanation would be great, especially if it has formula. Also, if I'm wrong about Tatooine, please let me know how/why. Thanks.

Your explanation about Tattoine is correct. In the book, "The Science of Star Wars", the writer goes in depth on how a binary and a tri-star system would work.

I agree with you that a system with six stars would be very complex for a planet orbiting. but if they were all very close to one another [meaning their distance from each other is less than one tenth than the distance form any of them to the planet], then it would work the same as a binary system does. and if all the stars are about the same mass, their gravitational pull on the planet will be like that on a massive star. but if neither of those statements are true, well, say goodbye to the planet.

It isn't really enough to have orbital stability; the orbit of the planet needs to be such that a roughly constant distance is maintained from the stars themselves, so as to not alternatively freeze-fry the planet.


It's not going to work in general--the resulting force will not be to the common barycenter. But the most straightforward way to ensure this is to make the planet at one of the two Trojan points of the binary system (imagine an equilateral triangle width one side between the two stars). With a fair mass ratio between the stars, the orbit will be stable, and maintain constant distance to the two stars. Unfortunately, that's not what happens in the movies, since from the planet's point of view, the stars should always remain at a 60-degree separation.

So the next best thing to make the planet a satellite of just one of them. Fortunately, the visual evidence suggests a very disparate actual size (the bluish-white one would be several times larger, so the the only reason they'd appear roughly equal is that one is closer; cf. Hertzsprung-Russel diagram).

The closest real analog would be a star cluster. If you did a brief study to see how n-body physics applies to a star cluster, you could then derive - in which systems are planets possible. You may also wish to include a study of binary star systems.