[填空题]
We saw earlier (Chapter 14) that the rate energy reachegc8.bt tlwy8.fwz *p,4m5d fbs the Earth from the S.k ix2u9n:trugeg2 7 q/.wqh kun (the "solar constant") is g.7ket :ihr29guux2qk. wq /n about $1.3 \times 10^3\ \text{W/m}^2$. What is
(a) the apparent brightness $l$ of the Sun, $\times 10^3\ \text{W/m}^2$
(b) the absolute luminosity $L$ of the Sun? $\times 10^{26}\ \text{W}$
