Hi guys, i have previously posted this question in the 'maths' section but had no reply, so i thought i would try my luck here. I'm having problems understanding the units of a cosmic ray flux graph. The cosmic ray flux is given in 'Counts/cm^2 s str', or the counts per cm squared, per second, per steradian. I understand that i have to multiply this graph by the solid angle of my detector, to get the flux in 'Counts/cm^2 s', but this is where i'm having problems. The flux values represent the flux of cosmic rays at the earth’s surface. To calculate the solid angle, i need to divide the area of my detector A, by r^2, which is the radius of the radiating sphere (distance from my detector on the earth's surface to the cosmic ray point source). Since the flux is for cosmic rays, how do i calculate the distance, or radius of the sphere? Am i going about this the wrong way? I also need to do this calculation for solar particles. Can someone please shed some light on this for me please? Thanks, Pete.