1. The problem statement, all variables and given/known data A super nova releases 1.9E45 J of energy over a 10 day period. It is 1560 ly from earth. A detector, facing the star, is a disk of radius 7cm. How much energy reaches the detector? (The detector is in orbit, so it can face the star for the entire 10-day period) 2. Relevant equations Intensity = Power / Area Surface area of disk = pi r ^2 light year = 10E16 m 3. The attempt at a solution First, I found the initial power of the supernova. 1.9E45Joules / 864,000 seconds (10 days) = 2.199E39 W Then, I found the initial intensity: this is where I was confused - does the supernova radiate energy as a sphere or a disk? I used a sphere (4 pi r^2) Intensity = 2.199E39 W / (4 pi (1560E16 m) ^2) = .719 W/m^2 Then I found the power that the disk receives: Power = Intensity * area = (.719 W/m^2)(pi (.07)m^2) = .011 W Then .011W * 864,000 seconds = 9562.9 Joules Not sure what I'm doing wrong?