Solar constant for Earth is 2.0 cal per cm^2 per minute. [1 cal=4.2...

Solar constant for Earth is 2.0 cal per $\mathrm{cm}^2$ per minute. $[1 \mathrm{cal}=4.2 \mathrm{~J}]$. Angular diameter of the Sun (as seen from the Earth) is $\frac{1^{{}^{{}^{\circ}}}}{2}$ (= half a degree). Treating Sun as a black body, its surface temperature is estimated to be nearly