I understand how coherent light can produce interference patterns with a thin oil film. However the sun is a spatially incoherent light source.
How can it be that at oblique incidence I still see colors caused by inteference. Because when at an angle, the rays that interfere come from different spatial positions of the sun. At normal incidence the light ray would interfere with itself and the interference effects depend on the temporal coherence.
I don't think I can use the Van Cittert-Zernike theorem here because I am considering two parallel rays which do not originate at the same point (Or can I assume this, because the sun is so far away?).