Diametric profile of the shadow cast by an opaque circular mask of radius R₀ = 10 km, illuminated by a monochromatic wave that provides a Fresnel scale of λ_F = 1.2 km. The profile has been obtained through the numerical integration of Eq. (16), where φ_a(R) ≡ 0. The blue profile shows the shadow within the limit of geometrical optics, while the black profile accounts for diffraction effects. The edge of the shadow displays the Fresnel fringes with typical spacings of λ_F (Eq. (15)), while the shadow center hosts the Poisson spot that peaks at the value of the flux far away outside the shadow, normalized here to unity. The upper red curve shows a shifted and expanded view of the Poisson spot. The fringes around the Poisson spot have a spacing of ${\lambda }_{\mathrm{F}}^2/R_0=0.144$ km (Eq. (28)).