Evidence for an Unusually Active Sune

Evidence for an unusally active sun since the 1940s comes from a new estimation of sunspots back to the ninth century. Many natural phenomena such as solar radiance and sunspots vary according to natural cycles. The variation is subject also to additional fluctuations (arising from as yet unexplained effects) which complicate any study which examines only a short time interval. The longer the baseline, the more confident one can be in drawing out historical conclusions. In the case of sunspots, the direct counting goes back to Galileo's time, around 1610. But earlier sunspot activity can be deduced from beryllium-10 traces in Greenland and Antarctic ice cores. The reasoning is as follows: more sunspots imply a more magnetically active sun which then more effectively repels the galactic cosmic rays, thus reducing their production of Be-10 atoms in the Earth's atmosphere. Be-10 atoms precipitate on Earth and can be traced in polar ice even after centuries. Using this approach, scientists at the University of Oulu in Finland (Ilya Usoskin, 358-8-553-1377) and the Max Planck Institute in Katlenburg-Lindau in Germany have reconstructed the sunspot count back to the year 850, nearly tripling the baseline for sunspot studies. They conclude that over the whole 1150 year record available, the sun has been most magnetically active (greatest number of sunspots) over the recent 60 years. (Usoskin et al., Physical Review Letters, upcoming article)