= Broadband planetary coherence estimate
For an unresolved incoherent luminous disc of <angular diameter> $\alpha$, transverse optical coherence has scale $\lambda/\alpha$; a uniform circular brightness profile puts its first zero at $1.21967\lambda/\alpha$. A receiver transmitting a continuous <frequency> band of width $\Delta\nu$ instead has <temporal coherence> scale $1/\Delta\nu$ and longitudinal length $c/\Delta\nu$. Angular source size and spectral filtering control different correlations. Atmospheric <phase> fluctuations and instrument averaging can further reduce measured fringe visibility.
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