1. The problem statement, all variables and given/known data Image attached 2. Relevant equations For circular orbit, r = Pv / 2 pi , Where P = orbital period and v=orbital velocity r' = r sini , where i is unknown angle to plane of sky. 3. The attempt at a solution I'm really not getting these binary problems at all. I would start by finding v, but how is this from them "the observed maximum velocity shift of 26.1 km/s" ? Then I would use r = Pv / 2 pi , and the separation would just be 2r as they are identical stars, is this right? I don't know where to start with the angle of inclination part. Also, in my notes, talking about binaries in general, it says that r1 + r2 = a I think that's r1= radius of star 1, r2 = radius of star 2, a = true semi-major orbital axis, but I don't understand this, how could the 2 radii total the semi-major axis? Surely it would be 2a if anything? And talking about the semi-major axis, does the system actually have a semi-major axis? I thought there was just one for each star. Really lost here, any help would be appreicated, thanks!