Is given by visibility function for an ellipse with a = b,
where
and is the angular radius and D the baseline distance. Therefore, the zeros in a plot of visibility amplitude versus baseline distance (V vs. D) occur when
where denotes the nth zero of the Bessel function and D is the angular diameter. The angular diameter is
The first few 's are 3.8317, 7.0156, 10.1735, 13.3237. The corresponding equations are
