Re:Imaging Cygnus a at 8.45 GHz with ATA
by petschge on Sunday August 08, 2021 @09:48PM
(#28111916)
Sorry, but that is simply wrong.
And yes, the inverse square law is strictly speaking only true for point sources. But it is an extremely good approximation once you are much further away than the size of the source (a distance ten times the diameter of the source is usually totally sufficient).
Re:Imaging Cygnus a at 8.45 GHz with ATA
by lend000 on Sunday August 08, 2021 @10:32PM
(#28112180)
I had to re-derive it for a perfect cone to be sure. You are correct; at a distance where the size of the cross section of the beam is significantly larger than the source, deviation from inverse square becomes negligible.
And yes, the inverse square law is strictly speaking only true for point sources. But it is an extremely good approximation once you are much further away than the size of the source (a distance ten times the diameter of the source is usually totally sufficient).