The mystery of the supernova that created the Cassiopeia A supernova remnant may have found a solution in the story of a daylight star seen at the time of the birth of King Charles II in 1630, astronomer Martin Lunn and historian Dr Lila Rakoczy have suggested at the Royal Astronomical Society’s National Astronomy Meeting in Llandudno, Wales.

It is estimated that a supernova explodes in our Milky Way Galaxy once every fifty to a hundred years, but the last galactic supernova to be seen was Kepler’s supernova in 1604. This poses a conundrum – whilst the majority of missing galactic supernovae can be explained away as being on the far side of the Milky Way where we cannot see them, their light blocked by intervening gas and dust, one cannot be explained away. This is the type IIb supernova that left behind the supernova remnant Cassiopeia A, which has been imaged by space telescopes such as Hubble and Chandra to stunning effect. Based on the physical parameters of this expanding cloud of stellar debris, astronomers have estimated that it was created sometime in the seventeenth century – 1670 is often a date that has been plumped for. But together Lunn and Rakoczy have come up with an alternative four decades earlier.

Lunn came across historical records from 1660 that describe how, in 1630 when the future king Charles II was born, a daylight star was seen in the midday sky with the Sun. He teamed up with historian Rakoczy, who also found references to the star in seventeenth century literature, including poems by the astronomer John Bainbridge. But if this ‘noon star’ was the supernova that created Cassiopeia A, 11,000 light years away in the constellation of Cassiopeia, why wasn’t it more widely seen? A type IIb supernova, which is the core collapse of a massive star, would only have been bright enough to have been seen in daylight for a week at most, says Lunn. A few cloudy days and nights and it may not have been widely noticed. However, now that historians and astronomers know what to look for, other evidence for a 1630 supernova may come to light.

“The number and variety of sources that refer to the new star strongly suggest that an astronomical event really did take place,” says Lunn. “Our work raises questions about the current method for dating supernovae, but leads to the exciting possibility of solving a decades-old astronomical puzzle.”