Q: In order to resolve a sun-like star at 10 pc,
     using pictures in visible light (550 nm),
     how large would a telescope's aperture have
     to be?  Remember that 10 pc = 3 x 10^(17) m.

        
        The diameter D of the telescope would have
        to be roughly

                                   wavelength
               D  =  (70 degrees) --------------
                                  angular size in degrees


                                    550 x 10^(-9) m
                  =  (70 degrees)  ---------------------
                                   1.7 x 10^(-7) degrees


                  =  226 m