Interferometric angular diameter ($V(B)=2J_1(\pi B\Theta /\lambda )/(\pi B\Theta /\lambda )$)

An angular diameter inferred from the interferometric visibility of an extended source. The displayed monochromatic formula is for a uniformly bright circular disk, with projected baseline $B$, diameter $\Theta$ and wavelength $\lambda$. Its first visibility zero gives $B\Theta /\lambda \simeq 1.22$. Stellar angular diameter from a visibility envelope describes this calibration; real photospheres require limb-darkening corrections.