The Crab, Tycho and Kepler SNRs are all remnants of supernovae that were observed when they exploded, the Crab by Chinese astronomers and Tycho and Kepler by the European astronomers whose names they now bear. Cassiopeia A is thought to have exploded about 300 years ago, though it's not clear that it was observed at the time, probably because it was obscured by dust.

Select an SNR to examine by clicking a button on the top right. This brings up a table below from which the optical, X-ray and radio images for each SNR can be viewed. The column entitled "Image" provides links to images in the available wavelength regions, whereas the the "Contour" columns provide an overlay of contours of either X-ray or radio emission. This set of images allows the comparison between any two of these wavelength regions.