  Eight models for the coherence of the quasi-monochromatic light from
spherical incoherent sources are constructed by placing incoherent monopole and
dipole sources on the surface of a sphere, inside a ball and on a plane
circular disk. All models allow relatively simple numerical calculations of
coherence functions for arbitrary source sizes and positions of observation
points. We show that the far-field regime for transverse coherence is formed at
the distances larger than the source size, regardless of the wavelength. Wide
angle far field coherences have simple analytical representations in terms of
the spherical and cylindrical Bessel functions. For very large sources the main
and few first lobes of coherence function is well represented by paraxial
approximation, which reduces the number of models to three. Based on the solar
images corresponding to these three models the ball model emerges as the most
appropriate. Ball model can be modified to match the limb darkening
observations.
