One of the problems that many people have with astronomy is that when they look through a telescope at a star or planet is that they do not see the grand pictures that we get from the Hubble Space Telescope, or any of the other large telescopes. Instead, many times all they see is a point of light, in the case of a star, or a fuzzy image, in the case of a planet. Astronomers also have a problem. Since we can look at a star from only one position in space, we cannot see the star in three dimensions. Everything looks flat and two dimensional.

The light from Cassiopeia A exploding into a supernova reached earth 330 years ago. This supernova remnant is located in the constellation of Cassiopeia, and is approximately 11,000 light-years away. Since we can only see this supernova from one angle, how did astronomers see it from a new angle? The solution was quite ingenious. Not all of the light from the supernova took the same path to reach us. Some of the light took a longer path by reflecting off clouds of interstellar dust. Astronomers have detected these echos of light. Since these echos of light come from a different view of the supernova, astronomers now have a different view.

But what did they find? They found that the supernova did not explode uniformly. Instead much of the explosion was focused in one direction. Gas from the supernova is streaming at a speed almost 4,000 km/sec, which is still just a fraction of the speed of light. As a consequence, the neutron star that resulted from the supernova is moving through space in the other direction at about 358 km/sec.

via : Astronomers See Historical Supernova from a New Angle
via : Direct Confirmation of the Asymmetry of the Cas A SN Explosion with Light Echoes