A charge-coupled device (CCD) attached to a telescope measures the wavelength at which maximum intensity of radiated energy from a star to be 400 nm and the power received at the Earth's surface per unit area to be 2.8×10−10 Wm−2 .
a. a Show that the surface temperature of the star is about 7300 K.
b. b At this temperature, the total power emitted by the star is determined to be 7.2×1027 W . Calculate how far away the star is from the Earth. Give your answer in standard form and in light-years.