I have a binary star system and have come up with some stats for it.

My primary star is an F-type, with a mass of 1.3 sols and a luminosity of 2.197 sols. My secondary star is a K-type, with a mass of 0.75 sols and a luminosity of 0.422 sols. They have an average separation of 0.2 AU and an eccentricity of about 0.4. My habitable planet sits about 2.05 AU away from this pair and, if my math is right, the two stars together have an apparent brightness of 11 sols from the surface of the planet.

My question: Is my secondary star visibly distinct from my primary star to someone standing on the surface of the planet?

I'm kind of hoping for something Tatooine-like (ie, two visibly distinct suns/stars), but I'm not sure that's what I created for myself. Thank you for your time and help!


1 Answer 1


Definitely yes.

0.2/2.05 gives you tangent of 0.09756, which corresponds to 5.57 degrees. For comparison, Sun and Moon's angular diameter is 0.5 degrees. Both of your stars will be clearly visible, and angular separation would seem to be even bigger than in Tatooine sky.

  • $\begingroup$ Separation would be even greater than in Tatooine sky? By how much, do you think? Or, rather, if my stars have an angular diameter of 5.57 degrees, what would the stat be for the Tatooine stars? $\endgroup$
    – z2a
    Commented Mar 29, 2018 at 0:24

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