SN 1181

The stationary star was blue-red in color with radiating points.

There's a description in the Azuma Kagami stating "the stationary star was blue-red in color with radiating points." This refers to the supernova explosion of the first year of Yōwa (1181), known as SN 1181. It states: "Around eight o'clock at night, a comet appeared in the northeast. The stationary star (Saturn) was blue-red in color, trailing like a comet's tail. There has been no such example since one appeared in 1006."

This supernova is said to have shone between Cassiopeia and Cepheus for about 185 days, and was also recorded as a "guest star" in Fujiwara no Teika's Meigetsuki. While "stationary star" originally means "Saturn," it probably referred to a star that resembled Saturn in appearance. They couldn't have known it was a star's final moments, so it's understandable they mistook it for a comet. Observation records of this supernova explosion remain not only in Japan but also in China.

Such celestial objects that suddenly appear in the sky, shine brightly, and then eventually disappear, like supernovae and comets, were called "guest stars." Even with old records, most of them have apparently been identified through modern astronomical observations. However, SN 1181 had remained unsolved for a long time, but a supernova remnant discovered in 2019 is now the leading candidate, with analysis results announced to match the historical descriptions.

It's a vivid nebula in the direction of Cassiopeia with a white dwarf at its center.


Multi-wavelength observation results of supernova remnants

(G. Ferrand and J.English, NASA/ Chandra/ WISE,ESA/ XMM,MDM/ R.Fessen, Pan-STARRS)

The research results on this supernova remnant were published last year, and the beautiful image above was included in the report article. If colors like those in this image were visible at the time, it's natural that they described it as "blue-red."