Relative visibility amplitude of Cygnus A (left) and the Sun (right) are shown as the solid curves. The short-dashed curve shows the point spread function of the observations, while the long-dashed curve a power-law approximation. The dotted curve is a sum of four (left) and three (right) Gaussians that approximates the measured spectra. Both the active (1999APR11) and quiet (1993NOV06) Sun are shown.