# Astro, flux & energy

The neutrino flux from supernova 1987A was estimated to be 1.3e14 m^-2 at the Earth. SN 1987A occured in the Large Magellanic cloud, which is located at a distance of 50 kpc. If the average energy per neutrino was 4.2 MeV, estimate the amount of energy released in the form of neutrinos during the supernova explosion

## Homework Equations

electron volt = 1.602e-19 J
pc = 3.086e16 m

## The Attempt at a Solution

I can't seem to get the answer... :(
any help will be appreciated :)
i was thinking since flux falls off ~ 1/d².
so i tried E = flux *d²*avg energy of neutrino
1.3e14*(50000*3.086e16)²*4.2e6*1.602e-19
=3.258e44 J.
So i'm off by more than a factor of 10... :(
What am i doing wrong??

malawi_glenn
the area of a spehere is $$4 \pi r^2$$