According to an Old English manuscript chronicling the history of the Anglo-Saxons, a mysterious “red crucifix” appeared in the “heavens” over Britain one evening in A.D. 774. Now astronomers say it may have been the supernova explosion that sprinkled unexplained traces of carbon-14 in tree rings that year, halfway around the world in Japan.
Jonathon Allen, an undergraduate student at the University of California, Santa Cruz, made the connection this week after listening to a Nature podcast. He heard a team of Japanese scientists discussing new research in which they measured an odd spike in carbon-14 levels in tree rings from the year A.D. 774 or 775. They thought the spike must have come from a burst of high-energy radiation striking the upper atmosphere and triggering an increase in the rate of carbon-14 formation.
(Carbon-14, a radioactive version of a carbon atom with six protons and eight neutrons, forms when gamma rays from space strip atmospheric atoms of their neutrons, which then collide with the isotope nitrogen-14 and cause it to radioactively decay into carbon-14.)
Astrolabe planisphèreAsne Michel (2e moitié 16e siècle-début 17e siècle) orfèvre à Caen(C) RMN / René-Gabriel Ojéda
An astrolabe (Greek: ἀστρολάβον astrolabon, “star-taker”) is an elaborate inclinometer, historically used by astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars, determining local time given local latitude and vice-versa, surveying, triangulation, and to cast horoscopes. It was used in classical antiquity, through the Islamic Golden Age, the European Middle Ages and Renaissance for all these purposes