On Cas A, Cassini, Comets and King Charles

TL;DR

This paper re-evaluates the date of the Cas A supernova, dismisses the 1630 noon-star hypothesis, and proposes a 1671 discovery by Cassini as the likely supernova event based on brightness and ejecta motion.

Contribution

It provides new evidence linking a 1671 star discovery by Cassini to the Cas A supernova, challenging previous 1630 event associations.

Findings

The 1630 noon-star is unlikely to be the Cas A supernova due to brightness and motion inconsistencies.

A 4th-magnitude star discovered by Cassini in 1671 matches expected supernova brightness and ejecta motion.

No prior records or observations support the 1630 event as the Cas A supernova.

Abstract

We re-examine the long-standing problem of the date of the Cassiopeia A supernova (SN), in view of recent claims that it might be the 1630 "noon-star" seen at the birth of King Charles II. We do not support this identification, based on the expected brightness of a Type-IIb SN (too faint to be seen in daylight), the extrapolated motion of the ejecta (inconsistent with a date earlier than 1650), the lack of any scientific follow-up observations, the lack of any mention of it in Asian archives. The origin of the 1630 noon-star event (if real) remains a mystery; there was a bright comet in 1630 June but no evidence to determine whether or not it was visible in daylight. Instead, we present French reports about a 4th-magnitude star discovered by Cassini in Cassiopeia in or shortly before 1671, which was not seen before or since. The brightness is consistent with what we expect for the Cas A SN; the date is consistent with the extrapolated motion of the ejecta. We argue that this source could be the long-sought SN.