What is the shape of the wavefront on Earth for sunlight?

(N/A) As shown in the figure,the Sun acts as a point source of light. The wavefronts emitted from the Sun are spherical in nature. However,because the distance between the Sun and the Earth is extremely large $(1.5 \times 10^{11} \ m)$,the radius of the spherical wavefront becomes very large. When observed locally in a finite region on Earth,a small portion of this large spherical wavefront appears to be almost flat. Therefore,for all practical purposes,the wavefront of sunlight reaching the Earth is considered to be a plane wavefront.