“Using a computer model simulation, Haruichi Washimi, a physicist at UC Riverside, has predicted when the interplanetary spacecraft Voyager 2 will cross the “termination shock,” the spherical shell around the solar system that marks where the solar wind slows down to subsonic speed….” http://www.sciencedaily.com/releases/2007/11/071127171052.htm
A Day in the Life of a Presson... 
fascinating – putt putt putt along
30 years to get to the bow shock where solar-emitted particles (solar wind) slow down to below the speed of sound. I wouldn’t have thought sound phenomena would be relevant in space, especially having an impact in visual spectrum. And what is slowing the particles down? Is it solar (system) gravity? Even more amazing is the “pause”, where the particles come to a stop(!).