Tottaly nailed it!.
Sun is geometry or coronas?... how about the moon... it has displacement to achieve the jagged border or it was happy coincidence?
Scene setup is prety easy, sun is Sphere with corona light mtl, moon is sphere with default gray corona mtl and prety large geometry noise above it, Both are puled away from camera in to max distance ~1km or more and both are gigantic.
For camera setup and realistic DOF i used 200mm lens and 2,8f 70mm dof overide.
For enviroment i used corona sky+sun set to 89.7 angle and placed just behind the spheres to achive correct collor of sunset and i used prety low values for both. Aroud .05-.03.