= Equal-brightness binary-star visibility
{title2=$g(Y)=g_\star(Y)\cos(\pi\beta Y/\lambda)$}
Let identical spatially incoherent stellar brightness profiles of equal integrated <flux> be displaced by projected angles $\pm\beta/2$ along an interferometer baseline. The Fourier shift property makes their normalized signed coherence $g(Y)=g_\star(Y)\cos(\pi\beta Y/\lambda)$. The observed visibility is its absolute value. The slow single-star envelope depends on each star's brightness profile, while the oscillatory factor records projected separation. Unequal <flux> prevents complete cancellation at the binary minima.
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