1. The problem statement, all variables and given/known data What is the minimum angular separation an eye could resolve when viewing two stars, considering only diffraction effects? 2. Relevant equations Rayleigh criterion: θ=(1.22*λ)/D 3. The attempt at a solution This problem doesn't give very much to go on so I think there's a trick I'm missing. I tried estimating using λ=550 nm and D≈5.0 mm (which I got from the problem just before it), but this was incorrect. Our book also states that the best resolution of the human eye is 5e-4 rad, although I'm not sure how they came by this number and it is not the correct answer. I'm not really sure where to go with this one though, especially given so little information.