Medieval Supernova Lit Earth’s Skies for Months

We modern folks love our supermoons, meteor showers, and planetary sightings. But citizens of 11th-century Earth had something even better: their own supernova.

Witnessed from Earth on April 30–May 1, 1006, the massive stellar explosion was—and still is—the brightest supernova in recorded history. Its light blanketed Earth for months, and may have been strong enough to read by. Today we call it SN 1006, but at the time nobody knew quite what to make of it.

Benedictine monks in Switzerland wrote of a star “glittering in aspect and dazzling the eyes, causing alarm.” Their brothers in Italy were less effusive, reporting simply that “a brilliant star gleamed forth.”

Egyptian physician and astronomer Ali ibn Ridwan wrote that “the sky was shining.” He calculated the supernova’s brightness as three times that of Venus. Observers in Iraq marveled at the star’s “dazzling rays.”

Rock carvings by the Hohokam people may depict the 1006 supernova. Image credit: John Barentine, Apache Point Observatory

Some modern astronomers believe early Native American people also documented the cosmic event. Carvings found on a rock in Arizona seem to illustrate both the supernova and its position in the sky. 

The more precise records of the explosion come from medieval Japan and China, where astronomers watched the skies with unmatched rigor and precision. Japanese observers called SN 1006 the “guest star” and described it as “like Mars … bright and scintillating.”

Nine separate Chinese accounts of the supernova attest to the intensity of its light. One source said it was so bright “one could scrutinize things.”

Supernovae are the biggest explosions in space, and can out-dazzle entire galaxies. They’re also the main source of heavy elements in the universe. When Carl Sagan famously said that we’re all made of “star stuff,” he was talking about the remains of SN 1006 and its kin.

The light show in 1006 was likely the consequence of a cosmic merger between two white dwarf stars. Each star was the size of a planet and had as much mass as the Sun. It's no wonder the explosion was so magnificent.

Just how bright was it? Pretty dang bright. In 2003, Frank Winkler of Middlebury College combined what was known about the explosion itself with recent measurements of the star’s chemical remains. At the explosion’s peak, Winkler concluded, “people could probably have read manuscripts at midnight by its light.”

Nobody had ever seen anything like it before, and nobody has since. The last time a supernova was visible from Earth without a telescope was 1604. That explosion was nothing compared to SN 1006. 

It’s not that supernova explosions are a rare event. Far from it: A star explodes somewhere in the universe once every second. Everything is exploding, all the time. Our universe is just so big that we almost never notice.