I'm an amateur novelist and trying to build the world of a novel. Its solar system has a different number of planets and the earth a different number of moons. I'd like to add some reality in terms of the gravity balance or the orbital period. So hopefully I can do some calculation using software.

The features I want

  • free software
  • can change the number, the diameter, the mass and the distance from the sun of the celestial bodies
  • can observe the movement of the celestial bodies from "a bird's-eye view" in the space
  • can view the sky from the earth surface with planets and moons

I googled with "physical simulator celestial bodies" and it didn't help me so much. I searched this forum with "n-body simulator" and "celestial simulator" to get no results at all.

If some of you know a good app, would you kindly tell me about it?

  • RollForFantasy has a very basic Solar System Creator which fulfills your first two features. Jan 5, 2023 at 18:33

1 Answer 1


The software Universe Sandbox (https://universesandbox.com/) meets most of your criteria. The only unmet criterion would be that it is not free software. But at $29.95 the cost is reasonable. I am not too familiar with it yet, but it does allow you to change numerous parameters, as shown in the screenshot of some of the parameter settings.

Screenshot of General simulation parameters

By default the simulation begins with the current layout of our solar system but the different parameters allow you to alter settings to produce the types of alternate realities that it seems you are interested in.

  • The only drawback to this is that you have to install Steam. I think you should have mentioned it as most of us do not want to install more things. Jan 3, 2023 at 23:21

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