Assuming the Sun to be a spherical body of radius $R$ at a temperature of $T \ K$,evaluate the total radiant power incident on Earth at a distance $r$ from the Sun. Where $r_0$ is the radius of the Earth and $\sigma$ is Stefan's constant.

• A
  $\frac{R^2 \sigma T^4}{r^2}$
• B
  $\frac{4\pi r_0^2 R^2 \sigma T^4}{r^2}$
• C
  $\frac{\pi r_0^2 R^2 \sigma T^4}{r^2}$
• D
  $\frac{r_0^2 R^2 \sigma T^4}{4\pi r^2}$