An international team of researchers led by ETH Zurich restored solar activity until 969.
To recover this information, scientists used measurements of radioactive carbon in tree rings. The results helped scientists better understand the dynamics of the Sun and allowed them to more accurately date organic materials using the C14 method.
What happens in the sun can only be observed indirectly. Sunspots, for example, show the degree of solar activity – the more sunspots are visible on the surface of the Sun, the more active the processes taking place inside it.
Although sunspots have been known since antiquity, they were only documented in detail after the invention of the telescope, about 400 years ago. Thanks to this, we now know that the number of spots changes according to the eleven-year cycle, and there are also periods of strong and weak solar activity, which also affects the climate on Earth.
However, earlier it was difficult to reconstruct how solar activity developed before the beginning of systematic recordings. An international research team traced the Sun’s eleven-year cycle back to 969 using measurements of the concentration of radioactive carbon in tree rings.
To reconstruct solar activity over a millennium, researchers used tree ring archives from England and Switzerland. These tree rings contain a tiny fraction of radioactive carbon C14, with only one in every 1,000 billion atoms being radioactive.
From the half-life of the C14 isotope, the concentration of radioactive carbon that was present in the atmosphere when the growth ring was formed can be derived. Since radioactive carbon is mainly produced by cosmic particles, which are more or less held back from the earth by the sun’s magnetic field – the more active the sun, the better it protects the earth – solar activity can be determined from changes in the concentration of C14 in the atmosphere.
As a result of their work, the research team found evidence of unusual solar reactions that occurred in 1052 and 1279. They could seriously disrupt electronic circuits on Earth and on satellites.