Assuming the Sun to be a spherical body of radius R at a temperature of TK, evaluate the total radiant powered incident of Earth at a distance r from the sun
where `r_0` is the radius of the Earth and `sigma` is Stefan's constant.

Options

A. `r_0^2R^2sigma T^4//4pir^2`
B. `R^2 sigma T^4//r^2`
C. `4pi r_0^2 R^2 sigma T^4//r^2`
D. `pi r_0^2R^2 sigmaT^4//r^2`

Answer

A