Just realised I used the sun's diameter in the formula instead of it's radius... Oops! I'll redo those numbers, using more accurate numbers for the sun's radius and the orbital distance of the earth (I was using approximations pulled from memory before).

Surface area of sun (more accurate): 2,400,000,000,000 square miles

Area covered at distance of earth: 110,000,000,000,000,000 square miles

Area covered at scepti's orbital distance: 2,700,000,000,000,000,000 square miles

Sorry about that folks!

Anyway, lets knock 11 0's off those numbers, and pretend they're square centimetres instead of square miles:

Energy emitted by 24cm^{2} of the sun's surface has spread out to cover 1,100,000cm^{2} by the time it gets to earth, and 27,000,000cm^{2} by the time it's reached scepti's orbital distance (assuming I haven't cocked up my maths this time).