We know that the brilliant star that was studied by Johannes Kepler in 1604 was a supernova in the constellation of Ophiuchus the Serpent Bearer. It reaches a maximum brightness of -2 making it brighter than Sirius the brightest star in the sky. It was the last supernova that was easily seen in our galaxy. However by studying supernova in other galaxies astronomers have been able to group supernova in two groups. These are type 1 and type 2.
Kepler’s star was believed to be a type 1 supernova these are stars that have a lack of hydrogen in the spectra and can be found anywhere in galaxies. Where as type 2 supernova show hydrogen in their spectra and can only be seen in the disks of galaxies and are caused by the collapse of the core of the star.
In 1604 when Kepler’s star was seen none of the modern technology that astronomers use today existed it appeared around 2,000 light years above the galactic disk suggesting that it was a type 1 but observations of the expanding gas shell tend to suggest it was a type 2 supernova.
Over 400 years after its discovery Kepler’s Star is still wrapped in mystery.