A research team led by Tomoro Sashida and Tomoharu Oka of Keio University in Tokyo, Japan, has succeeded in precisely measuring the expansion velocity of a shock wave of the supernova remnant W44. The ...

But what is the difference? If you ask any person on the street, they might say there is no difference. In non-physics use, they would be correct. However, in physics we have very specific definitions ...