$S_{1} =-\frac{P}{4 \pi R_{0}^{2}}=\frac{4 \pi R_{s}^{2} \cdot \sigma \cdot T_{s}^{4}}{4 \pi R_{0}^{2}}$

$=\sigma \frac{R_{s}^{2}}{R_{s}^{2}} \cdot T_{s}^{4}$ ....................$(i)$

where, $R_{s}=$ radius of sun,

$R_{o} =\text { radius of orbit, }$

$\sigma =\text { Stefan.Boltzmann constant and }$

$T_{s} =\text { temperature of sun. }$

Now, intensity of radiation received from steller body on carth's surface,

$S_{2} =\frac{\sigma\left(50 R_{z}\right)^{2}}{\left(2 \times 10^{10} R_{0}\right)^{2}} \cdot\left(2 T_{s}\right)^{4}$

$\Rightarrow \quad S_{2} =\frac{2500 \times 16}{4 \times 10^{2}} \times \sigma \cdot \frac{R_{s}^{2}}{R_{0}^{2}} \cdot T_{s}^{4}$

$\Rightarrow \quad S_{2}=10^{-16} S_{1} \quad$ (from Eq. $(i)$)

$\Rightarrow \quad \frac{S_{2}}{S_{1}}=10^{-16}$