The expanding cloud of material left over from the supernova now appears approximately 10 light-years (3 pc) across from Earth's perspective.

Possible explanations lean toward the idea that the source star was unusually massive and had previously ejected much of its outer layers.

Its discovery was reported in 1948 by Martin Ryle and Francis Graham-Smith, astronomers at Cambridge, based on observations with the Long Michelson Interferometer.

[9] Another suggestion from recent cross-disciplinary research is that the supernova was the "noon day star", observed in 1630, that was thought to have heralded the birth of Charles II, the future monarch of Great Britain.

[12] Cas A was scanned during another Aerobee rocket flight of 1 October 1964, but no significant X-ray flux above background was associated with the position.

In 1999, the Chandra X-Ray Observatory found CXOU J232327.8+584842,[17] a central compact object that is the neutron star remnant left by the explosion.

[18] In 2005 an infrared echo of the Cassiopeia A explosion was observed on nearby gas clouds using Spitzer Space Telescope.

With the new data it was concluded that this is unlikely the case and that the infrared echo was caused by thermal emission by dust, which was heated by the radiative output of the supernova during the shock breakout.

The recorded spectrum of the optical light echo proved the supernova was of Type IIb, meaning it resulted from the internal collapse and violent explosion of a massive star, most probably a red supergiant with a helium core which had lost almost all of its hydrogen envelope.