Calculating EM Radiation from a Star 13 Million Light-Years Away

[phy112]

Homework Statement

A certain star is 13 million light-years from Earth. The intensity of the light that reaches Earth from the star is 6 10-21 W/m2. At what rate does the star radiate EM energy?

Homework Equations

i know you have to convert lightyears to m. (1.23e17m) multiply this by 2 and multiply again by 4pi. Do you just multiply that answer by the intensity to get the answer?

The Attempt at a Solution

 

[Redbelly98]

Almost. You're correct except for the "multiply this by 2" part. Instead of multiplying by 2, you need the square of the distance to the star. (A sphere's surface area is 4πr², not 2r·4π)

 

[phy112]

Thanks!