Binary separation from visibility-zero spacing ($\Delta Y=\lambda /\beta$)

For two identical equally bright stars, zeros of the binary factor occur at $Y_j=(j+1/2)\lambda /\beta$, where $\beta$ is separation projected along the baseline. Their repeated spacing is $\Delta Y=\lambda /\beta$. Multiple samples separate these rapid zeros from zeros of a resolved stellar envelope. Baseline rotation is needed to recover an unknown two-dimensional separation direction; the first zero alone does not determine both diameter and separation.