Cassiopeia A

Lore & Background

The supernova that created Cassiopeia A is estimated to have first reached Earth near the 1660s (±30 years), though no definitive contemporary records exist. It is circumpolar at mid-Northern latitudes, which had extensive records and basic telescopes, so its omission is likely due to interstellar dust absorbing optical light. Possible observations include John Flamsteed's 1680 cataloging of a sixth-magnitude star 3 Cassiopeiae, which has no corresponding star at the recorded position, and a 'noon day star' in 1630 thought to herald the birth of Charles II, though that is more probably Venus.

Reader's Guide

Cassiopeia A is significant as one of the most studied supernova remnants, providing key insights into stellar evolution, nucleosynthesis, and supernova dynamics. Its discovery in 1948 marked a milestone in radio astronomy, and its decreasing flux density (0.97% per year at 1 GHz) makes it a unique calibrator. The detection of phosphorus in 2013 confirmed supernova nucleosynthesis of this element. The light echo observed in 2005 allowed reconstruction of the explosion's properties despite no direct observation, opening new methods for studying past astronomical events. Its central neutron star and asymmetric explosion challenge models of core-collapse supernovae.

Did You Know?

• Cassiopeia A is the brightest extrasolar radio source in the sky at frequencies below 1 GHz.
• The supernova light is estimated to have reached Earth near the 1660s, but no definitive records exist.
• In 2013, astronomers detected phosphorus in Cassiopeia A, confirming production in supernovae.
• The 2005 infrared echo observation was the first light echo of a supernova whose explosion was not directly observed.