>>12857014Electron microscopes (which are used to "see" things at these scales) basically shoot a beam of electrons through a magnetic field acting as a lens and then use detection of the beam on the other side like light exposure on a conventional image. So in the simplest terms the lighter areas are where the fewest electrons were detected in the return aperture because something (in this case the sub atomic particles) blocks the electrons from getting through.
In that particular image what you are seeing is basically the atomic shell of the atoms electrons, the nucleas would be far too small and has too many electrons wizzing around it to see.
